INHERITANCE STUDIES FOR POD SHATTERING IN COWPEA (Vigna unguiculata 
L. Walp.)  

 

 

 

 

 

 

BY 

 

 

 

JOSEPH ASHIADONTONG UTAM 
(SPS/19/MAG/00019) 

 

 

 

 

 

A DISSERTATION SUBMITED TO THE DEPARTMENT OF AGRONOMY, 
FACULTY OF AGRICULTURE, BAYERO UNIVERSITY KANO. IN PARTIAL 

FULFULMENT OF THE REQUIREMENTS FOR THE AWARD OF MASTERS OF 
SCIENCE IN AGRONOMY (PLANT GENETICS AND BREEDING) 

 

 

 

 

 

 

DECEMBER, 2025 



ii 
 

DECLARATION 

I hereby declare that this work is the product of my research efforts undertaken under the 

supervision of Professor S. G. Mohammed and has not been presented anywhere for the 

award of a degree or certificate. All sources have been duly acknowledged. 

 

 

………………………………….. 
JOSEPH ASHIADONTONG UTAM 

SPS/19/MAG/00019 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



iii 
 

CERTIFICATION 

This is to certify that the research work for this dissertation and the subsequent write-up by 

Joseph Ashiadontong Utam (SPS/19/MAG/00019) was carried out under my supervision. 

 

 

 

--------------------------------     ------------------------------ 
Professor S. G. Mohammed     Date 
(Supervisor) 
 

 

 

-------------------------------     ------------------------------- 
 Dr. A. S. Shaibu                           Date 
(Head of Department) 

 

 

 

 

 

 

 

 

 

 

 

 



iv 
 

APPROVAL 

This dissertation has been examined and approved for the award of Master of Science 

Degree in Agronomy (Plant Genetics and Breeding). 

 

 

---------------------------------------    ------------------------------- 
(External Examiner)      Date 
 

 

 
---------------------------------------    ------------------------------- 
        Date 
(Internal Examiner) 
 

 

 
---------------------------------------    ------------------------------- 
Professor S. G. Mohammed     Date 
(Supervisor) 
 

 

 
---------------------------------------    ------------------------------- 
Dr. A. S. Shaibu      Date 
(Head of the Department) 
 

 

 

---------------------------------------    ------------------------------- 
Professor A. Nasiru       Date 
(CPS Representative) 
 



v 
 

ACKNOWLEDGEMENT 

I am profoundly grateful to Almighty God for His unfailing kindness, provision, wisdom, 

and sustaining grace throughout the course of this research. The lessons, resilience, and 

growth gained during this journey are testimonies of His faithfulness. 

I wish to express my sincere appreciation to my Supervisor, Professor S. G. Mohammed, 

whose expert guidance, patience, critical insights, and academic mentorship shaped the 

depth and quality of this research. His dedication to ensuring excellence at every stage is 

deeply appreciated. I am equally grateful to Dr. Patrick Ongom of the International Institute 

of Tropical Agriculture (IITA) Kano Station for his immense support, thoughtful feedback, 

and sacrifice of time and resources. His commitment greatly enriched the scientific rigor 

of this study. 

My heartfelt thanks also go to the IITA for sponsoring this research and providing the 

enabling environment, facilities, and technical support required to successfully execute the 

work.  

Special appreciation goes to Dr. A. S., Shaibu for his continued encouragement, 

constructive advice, and unwavering support throughout this academic journey. I am 

sincerely grateful to the Head of Department, Agronomy, Professor A. Lado, as well as all 

the lecturers and staff of the Department of Agronomy. Their collective guidance, 

administrative support, and commitment to academic excellence played a significant role 

in making this research possible. 

With deep gratitude to my father, Rev. Godwin Utam, whose vision, sacrifice, and 

unwavering commitment to my education laid the foundation that brought me to this point 



vi 
 

before his passing. His legacy continues to inspire me. My appreciation also goes to my 

mother, Mrs. Regina Utam, whose prayers, encouragement, and support have been a 

constant source of strength. To my siblings, thank you for your love and belief in my 

abilities. Special thanks to Muneiwa, my partner, whose understanding, emotional support, 

and motivation made the challenging moments bearable. 

To everyone who contributed in one way or another, whether through guidance, assistance, 

friendship, or encouragement, I say thank you. This work is as much yours as it is mine. 

 

 

 

 

 

 

 

 

 

 

 

 



vii 
 

DEDICATION 

This research and the report are dedicated to God and my Parents, Rev and Mrs. Godwin 

Utam and everyone who is committed to the growth of the Agricultural sector, from 

research to production and the business of agriculture.  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



viii 
 

TABLE OF CONTENTS 

Declaration .......................................................................................................................... ii 

Certification ....................................................................................................................... iii 

Approval ............................................................................................................................ iv 

Acknowledgement .............................................................................................................. v 

Dedication ......................................................................................................................... vii 

Table of Contents ............................................................................................................. viii 

List of Tables ..................................................................................................................... xi 

List of Figures ................................................................................................................... xii 

Abstract ............................................................................................................................ xiii 

Chapter One ........................................................................................................................ 1 

1.0 Introduction ................................................................................................................... 1 

1.1 Background of the Study .............................................................................................. 1 

1.2. Problem Statement ....................................................................................................... 4 

1.3. Justification of the Study ............................................................................................. 5 

1.4. Objectives of the Study ................................................................................................ 5 

Chapter Two........................................................................................................................ 7 

2.0. Literature Review......................................................................................................... 7 

2.1. Overview of pod shattering .......................................................................................... 7 

2.1.1 Grain yield loss .......................................................................................................... 7 

2.1.2 Reduced harvest efficiency ........................................................................................ 7 

2.1.3 Seed quality decline ................................................................................................... 8 

2.1.4 Increased labour and cost ........................................................................................... 8 

2.1.5 Decreased market value ............................................................................................. 8 

2.2. Importance of Pod Shattering Inheritance Study in Cowpea. ...................................... 8 



ix 
 

2.3 Genetic Factors Influencing Pod Shattering in Cowpea ............................................... 9 

2.4. Inheritance of Pod Shattering in Cowpea .................................................................. 12 

2.4.1 Gene action .............................................................................................................. 12 

2.4.2 Epistasis ................................................................................................................... 13 

2.4.3 Heritability ............................................................................................................... 13 

Chapter Three.................................................................................................................... 15 

3.0 Materials and Methods ................................................................................................ 15 

3.1. Experimental Site ....................................................................................................... 15 

3.2 Experimental Materials ............................................................................................... 15 

3.3. Evaluation of the Genotypes ...................................................................................... 15 

3.3.1. Population development.......................................................................................... 17 

3.3.2. F1 population .......................................................................................................... 17 

3.3.3. F2 evaluation ........................................................................................................... 17 

3.4. Data Collection .......................................................................................................... 18 

3.4.1. Days to first and 50% flowering ............................................................................. 18 

3.4.2. Days to first and 90% pod maturity ........................................................................ 19 

3.4.3. Pod length ............................................................................................................... 19 

3.4.4. Pod diameter ........................................................................................................... 19 

3.4.5. Pod shattering.......................................................................................................... 19 

3.4.6. Pods twist ................................................................................................................ 19 

3.5.7. Number of twists along pod length ......................................................................... 20 

3.5 Data Analysis .............................................................................................................. 20 

Chapter Four ..................................................................................................................... 22 

4.0 Results and Discussion ............................................................................................... 22 

4.1. Results ........................................................................................................................ 22 



x 
 

4.1.1. Parental screening and selection ............................................................................. 22 

4.1.2. Inheritance study ..................................................................................................... 28 

4.1.3 F2 segregating pattern for pod shattering ................................................................. 28 

4.1.4 F2 segregating pattern for pod twist ........................................................................ 28 

4.1.5 Performance of f2 progeny ....................................................................................... 34 

4.1.6 Broad sense heritability study .................................................................................. 34 

4.1.7. Traits association .................................................................................................... 36 

4.1.8. Phenotypic, genotypic, and environmental correlations of pod shattering ............. 42 

4.2 Discussion ................................................................................................................... 44 

4.2.1 Parental screening and selection. ............................................................................. 44 

4.2.2 Frequency distribution of phenotypic data for pod shattering and pod twists ......... 44 

4.2.3. F2 segregation pattern for pod shattering ................................................................ 45 

4.2.4. F2 segregating pattern for pod twist ........................................................................ 46 

4.2.5. Mean performance of the f2 and parents ................................................................. 47 

4.2.6 Broad sense heritability............................................................................................ 49 

4.2.7 Character association ............................................................................................... 50 

Chapter Five ...................................................................................................................... 54 

5.0 Summary, Conclusion, and Recommendations .......................................................... 54 

5.1 Summary ..................................................................................................................... 54 

5.2 Conclusion .................................................................................................................. 56 

5.3 Recommendations ....................................................................................................... 57 

References ......................................................................................................................... 58 

 

 

 

 



xi 
 

LIST OF TABLES 

Table             Pages 

Table 1: List of cowpea genotypes used in the study ........................................................16 

Table 2: Theoretical Inheritance Ratios .............................................................................21 

Table 3: Mean squares for the analysis of variance for agronomic and pod 
shattering traits in cowpea ....................................................................................23 

Table 4: Mean Performance for growth, yield and pod shattering traits in cowpea ..........24 

Table 5: Genotype’s reaction to shattering ........................................................................27 

Table 6: Segregating pattern for pod shattering in three F2 populations involving 
3 crosses ...............................................................................................................32 

Table 7: Segregating pattern for pod twist in three F2 populations ...................................33 

Table 8: Comparative Mean Values of Parental and F2 Generations for pod 
shattering and pod twist ........................................................................................35 

Table 9: Broad sense heritability table of the F2 population for all three (3) 
crosses ..................................................................................................................36 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



xii 
 

LIST OF FIGURES 

Figure            Pages 

Figure 1.1: Cowpea production in Nigeria from 2010 to 2022............................................2 

Figure 4.1: Frequency distribution of phenotypic data for  pod shattering and  pod 
twists in F2 populations 1 (IT17K- 939-1-1 × IT17K-1267-2-1). ...................29 

Figure 4.2: Frequency distribution of phenotypic data for  pod shattering and  pod 
twists in F2 populations 2 (IT17K 939-1-1  × BB-POP-255-1). .....................30 

Figure 4.3: Frequency distribution of phenotypic data for  pod shattering and  pod 
twists in F2 populations 3 (APH-1-143  × APH-1-145). .................................31 

Figure 4.4: Pairwise correlation plot for population 1 .......................................................38 

Figure 4.5: Pairwise correlation plot for population 2 .......................................................40 

Figure 4.6: Pairwise correlation plot for population 3 .......................................................41 

Figure 4.7: Phenotypic, genotypic, and environmental correlations .................................43 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



xiii 
 

ABSTRACT 

This study was conducted to assess phenotypic variability in pod shattering among 
advanced cowpea genotypes and to elucidate the genetic inheritance of resistance to pod 
shattering. Thirty-six cowpea lines, including elite breeding lines and a wild relative, were 
evaluated under field conditions at the IITA Minjibir research station using a 6×6 alpha 
lattice design. Based on phenotypic screening, six parental lines were selected and crossed 
in a bi-parental mating scheme to generate three F1 populations, which were advanced to 
F2 in the screenhouse. The F2 populations were evaluated in the field based on a 
randomized complete block design. Data were collected on pod shattering and pod twist at 
physiological maturity, alongside other agronomic traits. Statistical analyses, including 
ANOVA, frequency distribution, segregation, heritability estimates, and character 
association studies, were performed using R and Microsoft Excel. The segregation patterns 
in the F2 populations revealed that pod shattering in populations 1 (IT17K-939-1-1 × 
IT17K-1267-2-1) and 2 (IT17K-939-1-1 × BB-POP-255-1) followed Mendelian 
inheritance models with 3:1, 13:3, and 9:7 ratios, indicating monogenic and digenic control 
with epistatic and complementary gene interactions. Population 3 (APH-1-143 × APH-1-
145) displayed complex segregation inconsistent with classical ratios, suggesting 
polygenic control. Broad-sense heritability (H²) estimates for pod shattering were high 
across populations: 82% (Pop 1), 74% (Pop 2), and 100% (Pop 3), while pod twist showed 
variable heritability (79%, 41%, and 100%, respectively), indicating differential 
environmental influence. Character association analysis showed strong positive 
correlations between pod shattering and pod twist, suggesting pleiotropy or close linkage. 
The observed segregation patterns and heritability estimates imply that genetic 
improvement for resistance to pod shattering in cowpea will benefit from population-
specific selection strategies, particularly targeting recessive alleles and gene interactions 
involved in the pod dehiscence. 

 

 

 

 

 

 



1 
 

CHAPTER ONE 

1.0 INTRODUCTION 

1.1 BACKGROUND OF THE STUDY 

Cowpea (Vigna unguiculata L. Walp.) is an important legume crop that is widely cultivated 

in various parts of the world, particularly in sub-Saharan Africa, Asia, and South America 

(Singh et al., 2011). It is a major source of protein and other essential nutrients for millions 

of people, especially in developing countries where access to animal protein is limited. 

Cowpea is also a significant crop for livestock feed due to its nutritious fodder and soil 

fertility improvement through nitrogen fixation (Timko et al., 2008). 

Cowpea is one of the most important legume crops globally due to its vital role in food and 

nutritional security, especially in sub-Saharan Africa. It is cultivated on an estimated 15 

million hectares worldwide, yielding approximately 9.8 million metric tons in 2022 (FAO, 

2023). Africa dominates cowpea cultivation, accounting for about 98% of the global 

harvested area and roughly 96% of total production. West Africa alone contributes around 

80% of the continent’s output, with the crop being a staple in many farming systems due 

to its adaptability to poor soils and drought-prone environments (FAO, 2023; Boukar et 

al., 2018). 

Nigeria is the world’s leading producer of cowpea, both in terms of area under cultivation 

and production volume (FAOSTAT, 2022). In 2021, Nigeria cultivated approximately 4.8 

million hectares of cowpea and produced an estimated 3.6 million metric tons (Figure 1.1). 

This accounted for about 61% of total cowpea production in Africa and roughly 37% of 

the global production, making it the largest single contributor to cowpea supply worldwide. 



2 
 

 

 

 

 

 

 

 

 

 

Figure 1.1: Cowpea production in Nigeria from 2010 to 2022. 

 

 

 

 

 

 

3,
37

0,
00

0

1,
64

0,
00

0

5,
15

0,
00

0

4,
63

0,
00

0

2,
14

0,
00

0

2,
31

0,
00

0

3,
75

0,
00

0

3,
87

0,
00

0

3,
75

0,
00

0

3,
80

0,
00

0

4,
13

0,
00

0

4,
21

0,
00

0

4,
13

0,
00

0

2 0 1 0 2 0 1 1 2 0 1 2 2 0 1 3 2 0 1 4 2 0 1 5 2 0 1 6 2 0 1 7 2 0 1 8 2 0 1 9 2 0 2 0 2 0 2 1 2 0 2 2

PR
O

DU
CT

IO
N

 V
O

LU
M

E 
(M

ET
RI

C 
TO

N
S)



3 
 

 

 

 

 The production trends over the past decade indicate a generally upward trajectory in 

cowpea output globally. However, contrary to some reports suggesting a steady increase 

in Nigeria’s cowpea production in 2022, FAOSTAT data indicated a slight decline, with 

total production estimated at 4.13 million metric tons compared to 4.21 million tons in 

2021. Nonetheless, Nigeria remains a key player in cowpea production, and its role is 

expected to remain significant given ongoing government and donor-supported agricultural 

initiatives aimed at improving legume productivity. 

Cowpea domestication is believed to have occurred in the Sahel region of Africa over 5,000 

years ago (Boukar et al., 2003). The domestication of cowpeas has played significant roles 

in improving the crop's productivity, nutritional value, and resilience to various biotic and 

abiotic stresses (Boukar et al., 2019). Over the years, farmers have selected cowpea with 

desirable traits such as high yield, early maturity, drought tolerance, resistance to pests and 

diseases and resistance to pod shattering.  

One of the major differences between domesticated cowpeas and their wild form is their 

response to shattering. The shattering trait is an adaptation phenomenon in wild varieties 

that causes seed dispersal (Niang et al., 2004; Huynh et al., 2018). This trait is undesirable 

in domesticated varieties. The domestication process has made selection against pod 

shattering a core objective in cowpea breeding programmes (Gebhardt et al., 2019). Pod 

shattering in cowpea is prevalent in arid and semi-arid regions and results in grain yield 



4 
 

losses (Lush et al., 1980; Funatsuki et al., 2014; Bandillo et al., 2017; Zhang et al., 2020; 

Parker et al., 2020). Also, in efforts to improve cultivated cowpea varieties by introducing 

resistance traits from wild relatives, unintended consequences such as the reintroduction of 

undesirable pod shattering traits have emerged. 

This occurs because the genes responsible for resistance and those controlling pod 

shattering may be closely linked or inherited together during the breeding process. As a 

result, some breeding lines, while successfully acquiring the desired resistance, also exhibit 

the undesirable shattering behavior characteristic of wild cowpeas. This further proves the 

need for careful selection and breeding to separate beneficial traits from unfavourable ones 

(Boukar et al., 2003; Timko and Singh, 2008). Therefore, it is important to evaluate the 

genetic basis of pod shattering with a view to develop cowpea varieties for resistance to it 

across different environments. 

1.2. PROBLEM STATEMENT       

Pod shattering is responsible for significant economic loss and reduced productivity in 

cowpeas. The spontaneous opening of mature pods and dispersal of seeds lead to seed/grain 

loss, reduced yield, and increased harvesting costs. Pod shattering in cowpea accounts for 

10 - 90% yield loss before and after harvest (Tofel et al., 2008; Ishiyaku et al., 2008; Singh 

et al., 2003). Despite the importance of cowpea as a staple food crop in many regions across 

the world, the genetic basis underlying pod shattering has not been fully understood. This 

knowledge gap hampers the development of effective strategies for breeding cowpea 

varieties with reduced pod shattering, limiting farmers' ability to maximize their yields and 

economic returns. 



5 
 

1.3. JUSTIFICATION OF THE STUDY 

Pod shattering is a core trait that was considered in the domestication of many crops, as 

seen in soybean, barley, and common bean. Pod shattering is an important dispersal 

mechanism in the wild, but it is one of the most common causes of yield loss in legumes 

before and during harvest. As a result, one of the first domestication traits to consider in 

shatter-prone crops is selection against shattering. Pod shattering in cowpea accounts for 

significant yield loss and further limits the economic gain in cowpea production. Therefore, 

this research aims to investigate the inheritance of pod shattering in cowpeas, providing 

more insights towards developing cultivars resistant to pod shattering for enhanced 

productivity. 

 

 

 

 

1.4. OBJECTIVES OF THE STUDY 

The objectives of this study were to; 

1. Determine the level of variation for pod shattering among advanced cowpea 

breeding lines. 

2. Assess the inheritance pattern of resistance to pod shattering in cowpeas. 

2.3.Determine the phenotypic and genotypic associations between pod shattering and 

selected agronomic traits in cowpea. 

 



6 
 

 

 

 

 

 

 

 

 

 

 



7 
 

CHAPTER TWO 

2.0. LITERATURE REVIEW 

2.1. OVERVIEW OF SHATTERING IN CROPS 

Pod shattering refers to the process in which mature pods of certain crop plants 

spontaneously open or break open, dispersing seeds before they can be harvested or during 

harvest. This phenomenon is primarily observed in plants with dry fruits or pods, such as 

cereals (e.g., rice, wheat), oilseeds (e.g., soybean, rapeseed), and legumes (e.g., peas, 

lentils), including cowpea (Ambrose et al., 2008). The natural mechanism of pod shattering 

evolved as an adaptation for seed dispersal in the wild. When the pods mature and dry, they 

undergo structural changes that cause them to split open, dispersing the seeds over a wider 

area (Simpson, 2019). However, in agriculture, shattering can have detrimental effects on 

crop production, including: 

2.1.1 Grain Yield Loss 

Shattering leads to significant yield losses as seeds are lost before harvest. The extent of 

yield loss can vary depending on the severity of shattering, crop species, and environmental 

conditions. Studies have reported yield losses ranging from 10 to 90% in cowpeas 

(Sugimoto et al., 2010; Wang et al., 2017). 

2.1.2 Reduced Harvest Efficiency 

Shattering increases the difficulty and cost of harvesting operations. Harvesting machinery 

may not effectively collect the seeds from the ground, and can also increase labour 

requirements. This can lead to additional economic losses for farmers. 



8 
 

2.1.3 Seed Quality Decline 

Seeds that are prematurely dispersed due to pod shattering may experience damage or 

exposure to unfavorable environmental conditions, such as moisture or pests. This can lead 

to a decline in seed quality, affecting germination rates and overall crop performance. 

2.1.4 Increased Labour and Cost 

Pod shattering can increase the labour and cost of harvesting, as farmers have to collect the 

seeds from the ground or use nets or bags to catch the falling seeds (Sassoume et al., 2021). 

2.1.5 Decreased Market Value 

Pod shattering can decrease the market value of crops, as the seeds may have lower quality, 

weight, and germination rate. 

2.2. IMPORTANCE OF POD SHATTERING INHERITANCE STUDY IN COWPEA 

The study of pod shattering inheritance in cowpea is important because it has not been fully 

unraveled yet. However, some researches have provided significant insight into its 

inheritance and creates room for further research and development initiatives (Parker et al., 

2021). Plant biologists and breeders alike are rapidly making progress in creating the 

needed tools to study and improve pod shattering resistance in cowpea (Timko and Singh, 

2008; Muñoz-Amatriaín et al., 2021). A thorough understanding of the inheritance of the 

trait is instrumental to attaining the full yield potential of cowpea (Parker et al., 2021). 

Understanding the inheritance of pod shattering can help breeders develop cultivars with 

reduced shattering (Dutta et al., 2019). Also, develop appropriate harvesting techniques 

and technologies to minimize losses and improve efficiency during harvesting (Daneji et 

al., 2016). Pod shattering can negatively impact seed germination, viability, and storability. 



9 
 

Dispersed seeds may have reduced vigor and shelf life, affecting their ability to establish 

healthy crops in subsequent seasons (Singh et al., 1999). By studying pod shattering, 

researchers can identify strategies to maintain seed quality and enhance seed storage 

techniques, ultimately benefiting farmers and the seed industry (Singh et al., 1999). 

Minimizing pod shattering reduces post-harvest losses and promotes sustainable farming 

practices. Research on pod shattering aligns with efforts to enhance the resilience and 

productivity of cowpea production systems while reducing environmental impacts 

(Gwathmey et al., 1999). 

2.3 GENETIC FACTORS INFLUENCING POD SHATTERING IN COWPEA 

Pod shattering in cowpea is a complex trait controlled by many genes. Early studies on 

legumes species, including cowpea, showed that pod shattering is primarily governed by 

Quantitative trait loci (QTLs) and not single gene loci, indicating the polygenic nature of 

the trait (Omoigui et al., 2006). Quantitative trait loci (QTLs) are specific genomic regions 

that control the expression of quantitative traits, such as pod shattering in cowpea (Lucas 

et al., 2011). QTL mapping has been widely employed to map the specific regions of the 

cowpea genome linked with pod shattering resistance. 

Ehlers et al. (2000) reported two major QTLs (qPSh1 and qPSh2) which control a 

consequential percentage of the phenotypic variance observed in pod shattering. Andargie 

et al. (2014) identified a QTL associated with pod shattering on chromosome 7 using 

mapping populations derived from crosses between wild and cultivated accessions. 

Suanum et al. (2016) identified a QTL on chromosome 11 also using mapping populations 

derived from crosses between wild and cultivated accessions. Fatokun et al. (2018) used 

QTL-seq analysis to identify QTLs associated with pod shattering resistance. The 



10 
 

identified QTLs provide valuable genetic markers that can be utilized in breeding programs 

to develop cowpea varieties with improved shattering resistance. The presence of these 

QTLs suggests that pod shattering resistance in cowpea is controlled by a few major loci, 

and can be exploited to overcome the constraint in cowpeas. Funatsuki et al. (2014) found 

that pod shattering in soybeans is controlled by a few major genes and loci, specifically the 

SHAT1-5 and PDH1 genes, which govern pod dehiscence through their role in lignin 

deposition and secondary cell wall development. Likewise, Takahashi et al. (2020) 

observed similar segregation patterns in rice, concluding that the phenotypic variation in 

shattering resistance was controlled by a few genes.  

The genetic basis for pod shattering relates to the biochemical composition, the lignin 

content of the pod walls and the structural integrity of the cell walls. Fang et al. (2014) 

reported that lignin biosynthesis-related genes are differently expressed in cowpeas 

resistant and susceptible to pod shattering. Enhanced mechanical strength due to increased 

lignin content in the pod walls results in greater resistance against shattering. 

During pod development, an abscission layer is formed at the base of the pod, which acts 

as a separation zone between the pod and the plant. This layer undergoes cell separation, 

resulting in the detachment of the pod from the plant when the pod is mature. However, in 

some cases, the abscission layer may not function properly, leading to premature pod 

opening and seed dispersal (Fang et al., 2014). Yang et al. (2017) identified specific genes 

involved in abscission layer formation and cell separation that contribute to pod shattering 

in cowpea. These genes control various molecular and physiological processes, including 

the regulation of cell wall modifications, cell separation, hormone signaling pathways, and 

transcription factors. 



11 
 

Zhao et al. (2019) used transcriptome analysis to identify genes associated with pod 

shattering in common bean. Since cowpea and common bean share genetic similarities, the 

identified genes could potentially be relevant to understanding the mechanism of pod 

shattering in cowpea as well. 

The timing of pod development is a critical factor influencing pod shattering. Some genes 

that control pod maturation are also involved in regulating pod shattering, particularly 

genes that delay the formation of the abscission layer, where shattering typically initiates. 

Ogbonnaya et al. (2007) found that delaying pod maturation allows for mechanical 

harvesting without premature pod opening, providing a genetic advantage in cowpea 

breeding programs aimed at reducing pod shattering. In soybean and common bean, 

research has identified key regulatory genes such as SHAT1, SHAT2, and SH4, which 

govern the timing of abscission layer formation and pod opening. While these specific 

genes have not been fully characterized in cowpea, ongoing research suggests that 

homologous genes could exist and play similar roles (Dong et al., 2014). The inheritance 

of pod shattering in cowpea is further complicated by epistasis, where interactions between 

different genes influence the overall expression of the trait. Diop et al. (2015) reported that 

certain gene combinations can either enhance or suppress pod shattering resistance, 

indicating that the genetic architecture of the trait is highly complex. A similar finding 

revealed that epistatic interactions involving major and minor genes significantly impact 

the inheritance of shattering resistance in legumes (Xu et al., 2017). 

Stress factors, such as drought and temperature, also play a role in the expression of pod 

shattering. Boukar et al. (2018) highlighted that certain cowpea genotypes are more prone 

to shattering under high temperatures, likely due to stress-induced weakening of the pod 



12 
 

walls. The interaction between genetic factors and environmental conditions complicates 

the inheritance of this trait, as some shattering-resistant varieties may shatter when grown 

in specific environments (Boukar et al., 2015). Ishiyaku et al. (2017) demonstrated that 

genotype-environment (GxE) interaction is a significant factor in cowpea pod shattering. 

They showed that while certain genotypes exhibit shattering resistance under optimal 

conditions, their resistance diminishes under stress conditions. This necessitates the need 

for developing cowpeas with stable resistance across environments. 

2.4. INHERITANCE OF POD SHATTERING IN COWPEA 

Understanding the inheritance of the pod shattering trait is important for breeding shatter-

resistant varieties. The inheritance involves a complex interplay of gene actions, including 

additive and non-additive effects, epistasis, and heritability, as well as environmental 

influences 

2.4.1 Gene Action 

The inheritance of pod shattering in cowpea is influenced by both additive and non-additive 

gene actions. Additive effects refer to the cumulative contribution of individual alleles, 

enabling breeders to achieve genetic improvement through selection (Falconer and 

Mackay, 1996). In cowpea, additive effects have been reported as significant in 

determining pod shattering, facilitating straightforward selection for resistant genotypes. 

Non-additive gene actions, including dominance and overdominance, also play an essential 

role. For instance, dominance effects, where one allele masks the expression of another, 

can contribute to pod shattering resistance, particularly in heterozygous genotypes (Singh 

et al., 2014). Mohammed et al. (2010) noted that both additive and dominance effects 

influence pod shattering in cowpea. 



13 
 

2.4.2 Epistasis 

Epistasis, the interaction between genes at different loci, is another critical factor 

influencing pod shattering. Studies on legumes suggest that traits such as pod wall strength 

and lignin content are governed by multiple interacting loci (Yu-Takahashi et al., 2020). 

In cowpea, Mohammed et al. (2010) demonstrated that epistatic interactions complicate 

the phenotypic expression of pod shattering, necessitating careful consideration in breeding 

programs. 

2.4.3 Heritability 

Heritability estimates provide insight into the extent to which genetic factors contribute to 

phenotypic variations. High heritability suggests a large influence of genotype in 

controlling the trait under consideration, and that selection would be effective in improving 

resistance. Mohammed et al. (2010) reported moderate-to-high broad-sense heritability for 

pod shattering in cowpea, indicating that genetic factors are a significant contributor. 

Narrow-sense heritability, which focuses on additive genetic variance, is often lower due 

to the influence of non-additive effects and environmental interactions. 

While additive gene actions enable effective selection, the presence of non-additive effects 

and epistasis necessitates advanced strategies such as marker-assisted selection (MAS) 

using identified QTLs can improve breeding precision, while high heritability estimates 

provide a strong foundation for achieving genetic gains. Advances in genetic studies, such 

as GWAS and QTL mapping, have shed light on the molecular mechanisms underlying the 

trait, offering valuable tools for breeding programs. Validating candidate genes and 

exploring their interactions with environmental conditions can help develop robust, shatter-

resistant cowpea varieties. 



14 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Formatted: Centered



15 
 

CHAPTER THREE 

3.0 MATERIALS AND METHODS 

3.1. EXPERIMENTAL SITE 

The experiment was conducted at the International Institute of Tropical Agriculture (IITA) 

Kano, Screen house located at Latitude 12° 0' 0.43" North and Longitude 8° 31' 0.19, and 

at its research station in Minjibir with geographical coordinates: 12° 10' 52" North, 8° 39' 

22" east all located in the Sudan Savannah Zone of Nigeria. 

3.2 EXPERIMENTAL MATERIALS 

A total of 36 cowpea genotypes including advanced breeding lines, recombinant inbred 

lines, local cultivars, landraces, and a wild relative were used in the experiment. All 

experimental materials were sourced from the International Institute of Tropical 

Agriculture (IITA), Kano station (Table 1).  

3.3. EVALUATION OF THE GENOTYPES 

Thirty-six cowpea genotypes were evaluated for pod shattering in the field from July to 

October 2022 at Minjibir research station. The experimental design employed was a 6×6 

Alpha Lattice design with two replications, two rows per plot, each row measuring 2m and 

1m spacing between plots. Two seeds were sown per hill. Hand weeding was carried out 

at 3th, 6th, and 10th weeks after planting. NPK 15:15:15 fertilizer was applied once, after the 

first weeding, when the plants were established vegetatively. Insecticides were applied at 

the same period to combat insect infestation. 

 

 



16 
 

Table 1: List of cowpea genotypes used in the study 
Genotypes   Attributes 
Aph-1-144 RIL from aphid-resistant population 
Aph-1-138 RIL from aphid-resistant population 
Aph-1-139 RIL from aphid-resistant population 
Aph-1-143 RIL from aphid-resistant population 
Aph-1-141 RIL from aphid-resistant population 
Aph-1-145 RIL from aphid-resistant population 
BB_S-POP2-255-2 RIL from aphid-resistant population 
IT17K-939-1-1 Advanced breeding line 
IT17K-1558-5-2 Advanced breeding line 
I08K-190-1 Advanced breeding line 
IT16K-1965-2 Advanced breeding line 
IT18K-253-2 Advanced breeding line 
IT17K-2024-7 Advanced breeding line 
IT18K-359-6 Advanced breeding line 
IT16K-2674-8 Advanced breeding line 
IT16K-2439-2 Advanced breeding line 
IT18K-311-1-2 Advanced breeding line 
IT16K-2315-5 Advanced breeding line 
IT16K-1937-2 Advanced breeding line 
IT17K-1267-2-1 Advanced breeding line 
IT17K-937-4-1 Advanced breeding line 
IT18K-726-1 Advanced breeding line 
IT17K-870-2-1 Advanced breeding line 
IT16K-2602-1 Advanced breeding line 
IT17K-2685-1 Advanced breeding line 
IT18K-313-4 Advanced breeding line 
IT17K-3267-2 Advanced breeding line 
IT18K-708-3 Advanced breeding line 
IT18K-414-2 Advanced breeding line 
IT99K-573-1-1 Released variety, resistant to striga 
IT08K-150-12 Released variety, resistant to striga 
ITT07K-297-13 Released variety, resistant to striga 
TVNu1158 Wild cowpea relative 
Danila Local cultivar 
Danmisira Local cultivar 
Achushiru Landrace, extra early maturity 

 



17 
 

3.3.1. Population Development 

Six (6) parental genotypes, 3 shattering (APh-1-145, IT17K-1267-2-1, and BB-S-POP2-

255-2) and 3 non-shattering (IT17K-939-1-1, IT17K-2024-7 and Aph-1-143) were used to 

create 3 unique F1 populations. The sowing of parental lines was done in two sets to create 

a staggered flowering time and to facilitate flower synchronization among different 

parents. The parents were sown in pots half-filled with topsoil, each pot having two plants. 

The plants were properly managed following all agronomic standards which included 

watering, fertilizer application, and spraying against insects. The crossing was conducted 

at the flowering stage following the procedure described by Ongom et al. (2021). At 

maturity, F1 pods were harvested, dried, threshed, and stored for the next evaluation phase. 

During the F1 evaluation, the F1 plants were allowed to self-pollinate to generate the F2 

seeds. The number of F2 seeds was 40-60 seeds per cross. 

3.3.2. F1 Population 

The F1 population generated from the parental crosses was grown in the screen house. Five 

(5) pots were used for each cross. These were advanced to the F2 generation and 

accomplished from October 2022 to January 2023. 

3.3.3. F2 Evaluation  

Evaluation of the F2 was carried out on in the field. The experimental design used was a 

Randomized Complete Block Design (RCBD) with two replications. Agronomic and 

phenotypic data were collected through the vegetative and reproductive phases of the crop, 

and pod shattering data was taken at pod maturity. To determine the inheritance pattern of 

resistance to pod shattering, segregation analyses were performed using classical 

Mendelian ratios, including 3:1 (single gene dominance), 9:7 (complementary gene 



18 
 

interaction), 13:3 (dominant and recessive epistasis), and 27:37 (modified dihybrid ratios). 

The observed phenotypic frequencies in the F₂ populations were compared with expected 

ratios using the Chi-square (χ²) goodness-of-fit test to infer the most probable genetic 

models. 

In addition to segregation analysis, frequency distribution curves were plotted for the 

measured traits (pod shattering, pod twist, pod diameter, pod length, etc.) to assess the 

nature of variation (continuous or discrete) and to infer whether traits were governed by 

major genes or polygenic inheritance. Further, broad-sense heritability (H²) was estimated 

to quantify the proportion of total phenotypic variance attributable to genetic variance. 

Trait association analysis was conducted using Pearson’s correlation coefficient to identify 

the strength and direction of relationships between pod shattering and other measured traits, 

particularly pod twist and number of twists, which are morphologically and functionally 

related. All statistical analyses were performed using R Studio for ANOVA and heritability 

estimation, while Microsoft Excel was used for chi-square segregation tests, frequency 

distributions, and graphical representations. 

3.4. DATA COLLECTION 

10 pods from 5 Plants per plot were harvested at physiological maturity and dried in a 

glasshouse for 4 weeks and data was collected thereafter. Pods were assessed for pod 

shattering using the following parameters as proposed by Yu-Takahashi et al. (2020). 

3.4.1. Days to First and 50% Flowering 

Data for days to first and 50% flowering were collected by recording the number of days 

from sowing to when the first flower was seen on the plant.  and also similarly, 50% 

flowering was recorded when about 50 % of the plants have flowered. 



19 
 

3.4.2. Days to First and 90% Pod Maturity 

Data was collected by recording the date when the first matured pod was seen and the date 

when about 90% of the pods mature. This was recorded when the pods were seen to have 

attained physiological maturity characterized by a change in pod color, and progressively 

drying. 

3.4.3. Pod Length 

Pod lengths were measured from the peduncle to the pod tip using a meter rule calibrated 

in centimeters (cm). 

3.4.4. Pod Diameter 

Pod diameter was measured using a digital vernier caliper calibrated in millimeters (mm). 

This was measured on sample pods collected from the net plot. Measuring the back of the 

whole pod that hasn’t split. 

3.4.5. Pod Shattering 

The pod shattering percentage was obtained by dividing the number of pods that shatter by 

the total number of pods collected as samples (10) and then multiplying by 100. 

Number of pods that shatter ×  100  
  Total number of pods collected as samples × 1

 

3.4.6. Pods Twist 

The number of shattered pods that twist were counted. This was obtained by dividing the 

number of pods that twist by the total number of pods collected as samples (10) and then 

multiplied by 100. 

Number of pods that twist ×  100  
  Total number of pods collected as samples × 1

 



20 
 

3.5.7. Number of Twists along Pod Length 

This was obtained by counting the number of twists along individual pods in the sample. 

In addition, the extent of shattering was rated on a scale of 1-5 based on the percentage of 

shattered pods from the 10 sampled plants in a plot according to Zhang et al. (2020), where; 

1- 9%, No shattering (Resistant). 

10 -100%, pod shattering (susceptible). 

3.5 DATA ANALYSIS 

All data collected was subjected to the Analysis of variance (ANOVA) using R studio 

analysis software and Microsoft Excel. For the F2 population, segregation pattern analysis 

was evaluated for each member of the population to determine the possible number of 

genes involved. Theoretical genetic ratios were used to determine the nature of inheritance 

(Table 2). Broad-sense heritability (H²) for pod shattering was calculated using the 

formula: 

𝐻𝐻2 =
𝜎𝜎𝐺𝐺2

𝜎𝜎𝑃𝑃2
× 100 

where:  𝜎𝜎𝐺𝐺2= genotypic variance, 

𝜎𝜎𝑃𝑃2= total phenotypic variance (genotypic + environmental variance). 

Heritability estimates were interpreted using the following thresholds: 

Low: H² < 30% 

Moderate: 30% ≤ H² ≤ 60% 

High: H² > 60% 

These classes follow the classification proposed by Robinson et al. (1949) and widely used 

in quantitative genetics. 



21 
 

Table 2: Theoretical Inheritance Ratios 
Ratio Number of Genes Attributes 

3:.1 1 A classic Mendelian monohybrid cross where one allele is 

completely dominant. 

9:.7 2 A non-Mendelian Complementary gene action  

13:.3 2 A non-Mendelian Dominant Suppressive gene action 

27:.37 3  Complex Gene Interactions 

(Ongom et al., 2012) 

 

 

 

 

 

 

 

 

 

 

 

 



22 
 

CHAPTER FOUR 

4.0 RESULTS AND DISCUSSION 

4.1. RESULTS 

4.1.1. Parental Screening and Selection 

The results from the analysis of variance for the screened parental genotypes revealed 

significant differences (P <0.05), for all pod shattering related and maturity traits (Table 

3). Significant genotypic variation was observed across the traits studied, as indicated by 

the analysis of variance (ANOVA). For pod shattering-related traits; pod twist had a mean 

square of 0.35 (p < 0.01), and pod shattering itself had a mean square of 14.83 (p < 0.01). 

The number of twists per pod, another mechanical trait, also showed significant genotypic 

variability (mean square = 11.30, p < 0.01), These variations reflect heritable differences 

that may be exploited in breeding programs aiming at reducing pod shattering. Pod 

morphological traits such as pod diameter (mean square = 1.61, p < 0.01) and pod length 

(mean square = 5.78, p < 0.01) also demonstrated statistically significant differences 

among genotypes. The phenological traits; days to first flowering (DFFL) and days to 50% 

flowering (D50FL) exhibited significant and highly significant differences (mean squares 

= 80.53 and 105.81 respectively, p < 0.05 and p < 0.01). Days to first pod maturity (DFPM) 

and days to 95% physiological maturity (D90PM) had mean squares of 71.47 and 89.16 

(both p < 0.01), also showing significant differences in maturity duration among genotypes.  

The mean performance for the genotype screening is presented in Table 4. The genotypic 

evaluation of thirty-six cowpea lines revealed considerable variation in growth, yield-

related, and pod shattering traits, indicating a wide genetic base. 



23 
 

Table 3: Mean squares from the analysis of variance for agronomic and pod shattering traits in cowpea 
    MS 

 

SOV Df DFFL D50FL DFPdMAT D95PdMAT Pdlength Pddiameter Pdtwist Pdsha Notwst 

Rep 1 8.23 8.93 43.21 28.93 0.028 0.1373 0.04ns 0.147 0.071 

Rep: Block 10 25.1 13.78 25.78 22.63 1.004 0.1559 0.027ns 0.44 1.703 

Genotype 34 80.53 * 105.81 * * 71.47 ** 89.16 ** 5.779 ** 1.606** 0.35** 14.83** 11.298** 

Residuals 23 39.32 28.7 22.98 16.64 1.978 0.1344 0.03 1.279 1.07 

ns: Non significant deviation. DF=degree of freedom, pdtwist_log =  pod twist log, pdshat =  pod shattering,  twist length, pdlength =  pod length,  
pod diameter, DFFL = Days to first flowering, D50FL = Days to 50% flowering, DFPdmat = days to first pod maturity, D95PdMAT = days to 90% 
pod maturity, Rep = Replication, SOV = source of variance.  

 

 



24 
 

Table 4: Mean Performance for growth, yield and pod shattering traits in cowpea 
Genotype Pdtwist Pdshat Notwst pddiameter PdLngth DFFL D50FL DFPdMAT D95PdMAT 
Achishiru 1.29cde 1.40bcd 3.0bcd 5.88h 12.01hij 46.00efg 49.00gh 67.00f-i 77.00kl 
Aph-1-138 1.96a 2.00a 8.0a 6.50h 12.84g-j 48.00efg 50.50fgh 66.00hi 78.50jkl 
Aph-1-139 1.98a 1.98a 7.30a 6.24h 13.06f-i 61.00a-d 64.00b-e 81.00bc 93.50bcd 
Aph-1-141 0.70f 0.70e 0.00e 7.70efg 13.96d-i 49.50c-g 51.00fgh 69.00d-i 81.00h-l 
Aph-1-143 0.70f 0.70e 0.00e 8.22b-f 15.00c-g 42.50g 50.50fgh 66.00hi 76.50l 
Aph-1-144 1.70ab 1.73abc 4.60b 6.21h 11.50ij 57.50a-e 61.00b-f 67.50e-i 97.50b 
Aph-1-145 1.99a 2.00a 8.10a 6.28h 10.04j 62.00abc 66.50a-d 78.00bcd 88.50c-h 
BB_S-POP2-255-2 1.26cde 1.31bcd 2.15cd 7.55efg 13.84d-i 43.50fg 46.50h 65.00i 81.50g-l 
Danila 0.70f 0.70e 0.00e 7.58efg 14.21c-i 49.00d-g 52.50fgh 74.50b-i 91.50b-e 
Danmisira 0.70f 0.70e 0.00e 7.40g 14.39c-i 56.00a-f 75.50a 92.50a 109.50a 
IT08K-150-12 0.70f 0.94de 0.00e 9.10a 15.20b-g 52.50b-g 54.50e-h 70.50d-i 85.00e-k 
IT08K-190-1 0.70f 0.70e 0.00e 7.47fg 13.54e-i 56.50a-e 61.00b-f 77.00b-e 88.00c-i 
IT16K-1937-2 0.70f 0.94de 0.00e 8.47a-d 16.02a-e 64.50ab 66.50a-d 78.00bcd 90.50b-f 
IT16K-1965-2 0.70f 0.70e 0.00e 8.86ab 12.50g-j 47.50efg 51.50fgh 70.50d-i 87.50c-i 
IT16K-2315-5 1.40bcd 1.78ab 2.00de 8.13b-g 14.32c-i 50.50c-g 52.50fgh 77.00b-e 89.50b-g 
IT16K-2439-2 0.70f 0.70e 0.00e 8.69a-d 15.40b-g 54.50a-g 58.00d-g 77.00b-e 86.50d-j 
IT16K-2602-1 1.05e 1.68abc 1.50de 8.85ab 16.12a-e 55.50a-f 59.00c-g 74.50b-i 90.00b-f 
IT16K-2674-8 0.70f 1.30cd 0.00e 7.99c-g 15.02c-g 66.00a 70.50ab 78.00bcd 93.50bcd 
IT17K-1267-2-1 1.53bc 1.70abc 3.00bcd 8.82ab 16.99abc 49.00d-g 52.00fgh 70.00d-i 83.00f-l 
IT17K-1558-5-2 0.70f 0.95de 8.00a 9.09a 13.73d-i 51.50c-g 54.50e-h 73.00b-i 84.00e-l 
IT17K-2024-7 0.70f 0.70e 7.30a 8.78ab 14.55c-h 50.00c-g 54.00e-h 76.00b-g 90.00b-f 
IT17K-2685-1 0.70f 0.70e 0.00e 8.16b-g 13.93d-i 51.00c-g 54.00e-h 70.00d-i 84.00e-l 
IT17K-3267-2 0.70f 0.70e 0.00e 8.50a-d 14.25c-i 58.50a-e 64.00b-e 75.00b-h 92.00b-e 
IT17K-870-2-1 1.18de 1.60abc 4.60b 8.29b-e 15.88a-f 49.50c-g 53.50e-h 72.00c-i 85.50d-j 
IT17K-937-4-1 0.70f 0.70e 8.10a 8.83ab 16.01a-e 46.00efg 50.00fgh 66.50ghi 79.00jkl 
IT17K-939-1-1 0.70f 0.70e 2.15cd 9.06a 18.36a 46.00efg 49.00gh 65.50hi 78.50jkl 
IT18K-253-2 0.70f 0.70e 0.00e 8.24b-e 14.11c-i 66.00a 69.50abc 82.50b 95.00bc 



25 
 

IT18K-311-1-2 0.70f 1.70abc 0.00e 8.65a-d 14.41c-h 48.50d-g 51.00fgh 72.50c-i 84.50e-l 
IT18K-313-4 0.70f 0.94de 0.00e 8.70abc 16.50a-d 61.00a-d 64.00b-e 76.50b-f 89.50b-g 
IT18K-359-6 0.70f 0.70e 0.00e 7.66efg 13.32e-i 55.00a-g 58.50c-g 74.50b-i 85.50d-j 
IT18K-414-2 0.70f 0.94de 0.00e 8.15b-g 13.88d-i 50.50c-g 53.50e-h 78.00bcd 85.50d-j 
IT18K-708-3 0.70f 1.05de 0.00e 8.46a-d 14.11c-i 50.50c-g 52.50fgh 67.50e-i 80.00i-l 
IT18K-726-1 0.70f 0.70e 2.00de 7.94d-g 15.37b-g 62.00abc 67.00a-d 81.00bc 91.5b-e 
IT99K-573-1-1 0.70f 0.94de 0.00e 8.53a-d 18.05ab 50.00c-g 51.50fgh 67.00f-i 80.00i-l 
ITT07K-297-13 0.70f 0.70e 1.50de 8.75ab 14.85c-h 51.50c-g 54.50e-h 72.00c-i 84.50e-l 
Mean 0.94 1.09 2.09 8.05 14.49 53.11 56.96 53.39 86.79 
Min 0.70 0.70 0 5.88 10.04 42.5 46.5 65 76.9 
Max 1.98 2.00 8.1 9.1 18.36 66 75.5 92.5 109.5 
cv% 17.41 21.24 83.38 4.56 9.7 11.8 9.41 6.53 4.69 
LSD 0.34 0.48 2.11 0.76 2.9 12.92 11.06 9.89 8.42 

Avpdtwist_log =  pod twist log, Avpdshat =  pod shattering,  twist length, avpdlength =  pod length,  pod diameter, DFFL = Days to 
first flowering, D50FL = Days to 50% flowering, DFPdmat = days to first pod maturity, D95PdMAT = days to 90% pod maturity. 



26 
 

The mean pod twist and pod shattering scores across genotypes were 0.94 and 1.09, 

respectively, with observed values ranging from 0.70 (non-shattering) to 1.98 and 2.00 

(highly shattering), confirming the presence of both highly shattering and shatter-resistant 

genotypes in the population. Aph-1-145, Aph-1-139, and Aph-1-138 recorded the highest 

pod shattering and twist scores, alongside elevated numbers of pod twists (≥7.3), 

categorizing them as highly susceptible lines. In contrast, genotypes such as Danila, 

Danmisira, Aph-1-143, and IT17K-2024-7 consistently recorded the lowest values for 

these traits, including zero pod twist, signifying strong resistance to pod dehiscence. 

Yield-related traits such as pod length and diameter also displayed considerable variation, 

with pod length ranging from 10.04 cm to 18.36 cm and a population mean of 14.49 cm. 

IT17K-939-1-1, a non-shattering line, exhibited the longest pod length (18.36 cm). Pod 

diameter had a mean of 8.05 mm, ranging from 5.88 mm in Achishiru to 9.10 mm in 

IT08K-150-12. Genotypes with higher pod diameters tended to show moderate resistance 

to shattering. Phenological observations revealed a mean of 53.11 days to 50% flowering 

(D50FL) and 86.79 days to 95% pod maturity (D95PdMAT). 

Flowers were first observed in IT18K-2674-8 and IT18K-233-2, while Aph-1-143 was the 

last to flower.  Damisira was the first to reach 50% flowering while BB-S-POP2-255-2 was 

the last to reach 50% flowering. Damisira was also the first to attain first pod maturity and 

90% pod maturing while BB-S-POP2-255-2 showed late pod maturity, and Aph-1-143 was 

the last to attain 90% pod maturity. 

Based on the quantitative parameters for pod shattering described above the 36 genotypes 

were categorized into shattering, and resistant to shattering (Table 5) 



27 
 

Table 5: Genotype’s reaction to shattering 
Susceptible to shattering Resistant to shattering 
Achishiru Aph-1-141 
Aph-1-138 Aph-1-143 
Aph-1-139 Danila 
Aph-1-144 Danmisira 
Aph-1-145 IT08K-150-12 
IT16K-2315-5 IT08K-190-1 
IT16K-2602-1 IT16K-1937-2 
IT17K-1267-2-1 IT16K-1965-2 
IT17K-870-2-1 IT16K-2439-2 
IT17K-937-4-1 IT16K-2674-8 
IT17K-939-1-1 IT17K-1558-5-2 
IT18K-311-1-2 IT17K-2024-7 
TvNu1158 IT17K-2685-1 
 IT17K-3267-2 
 IT18K-313-4 
 IT18K-359-6 
 IT18K-414-2 
 IT18K-708-3 
 IT18K-726-1 
 IT99K-573-1-1 
 ITT07K-297-13 
 IT18K-253-2 

 

 

 

 

 

 

 

 

 



28 
 

4.1.2. Inheritance Study 

The inheritance study was conducted in the F2 population where the progenies had 

maximum segregation for pod shattering. The F2 distributions for both pod shattering and 

pod twist were skewed to the left for all the populations. The highest number of F2 

individuals fell on the left (non-shattering) tail of the distribution with just a few occupying 

the right (shattering) tail as shown in Figures 4.1, 4.2 and 4.3. 

4.1.3 F2 Segregating Pattern for Pod Shattering 

The segregating F2 population 1 (IT17K- 939-1-1 × IT17K-1267-2-) expressed significant 

deviation from the 27:37 and 9:1 inheritance ratios. The inheritance favoured the 3:1 and 

13:3 ratios. The IT17K 939-1-1 × BB-POP-255-1 segregating F2 population 2 showed a 

significant difference from the 27:37 and 13:3 inheritance ratios and expressed non-

significance to 3:1 and 9:7 inheritance ratios. The F2 population 3 (APH -1-143 × APH-1-

145) expressed significant deviation from the four inheritance ratios it was tested as shown 

in Table 6. 

4.1.4 F2 Segregating Pattern for Pod Twist 

The segregating populations have expressed varying results when tested for pod twist using 

the four inheritance ratios (3:1, 9:7, 13:3 and 27:37). The F2 population 1 (IT17K- 939-1-

1 × IT17K-1267-2-) expressed significant deviation from 3:1, 13:3 and 27:37 inheritance 

ratios. The 9:7 ratio showed no significant deviation. The F2 population 2 (IT17K 939-1-1 

× BB-POP-255-1) tested non-significant to 3:1 and 13:3 inheritance ratio while, 9:7 and 

27:37 inheritance ratio expressed significant deviation. The segregating F2 population 3 

(APH-1-143 × APH-1-145) tested non-significant to the 9:7 inheritance ratio and showed 

significant difference for other three inheritance ratios (Table 7).  



29 
 

 

pod shattering, pod twists, pop 1 = population 1. 

Figure 4.1: Frequency distribution of phenotypic data for  pod shattering and  pod twists in F2 populations 1 (IT17K- 939-1-1 
× IT17K-1267-2-1). 

pod shattering

pr
og

en
y 

Co
un

t

0
5

10
15
20
25
30
35
40

Pop 1

pod twists

pr
og

en
y 

Co
un

t
0
5

10
15
20
25
30
35
40
45
50

Pop 1

IT17K- 939-1-1 

 

IT17K-1267- 2-1 

 

 IT17K- 939-1-1 

IT17K- 939-1-1 

 

IT17K-1267- 2-1 

 

 IT17K- 939-1-1 



30 
 

 

pod shattering, Av pod twists =  pod twists, pop 2 = population 2 

Figure 4.2: Frequency distribution of phenotypic data for  pod shattering and  pod twists in F2 populations 2 (IT17K 939-1-1  
× BB-POP-255-1). 

 

 

pod shattering 

Pr
og

en
y 

co
un

ts

0

5

10

15

20

25

30

35

40

Pop 2

Pod Twists 

Pr
og

en
y 

co
un

ts

0
5

10
15
20
25
30
35
40
45

Pop 2

IT17K 939-1-1 
IT17K 939-1-1 

BB-POP-255-1 
BB-POP-255-1 



31 
 

 

pod shattering, pod twists, pop 3 = population 3.  

Figure 4.3: Frequency distribution of phenotypic data for  pod shattering and  pod twists in F2 populations 3 (APH-1-143  × 
APH-1-145). 

 

 

Pod shaterring 

Pr
og

en
y 

co
un

t

0
2
4
6
8

10
12
14
16

Pop 3

Pod twists 

Pr
og

en
y 

co
un

t

0

5

10

15

20

25

Pop 3

APH-1-143 
APH-1-143 

APH-1-145 
APH-1-145 



32 
 

Table 6: Segregating pattern for pod shattering in three F2 populations involving 3 
crosses 
    X2 under different model ratios 
Crosses S:NS Ratio 03:01 09:07 13:03 27:37:00 
  Obs 

    

IT17K- 939-1-1 × IT17K-1267-2-
1 (Pop 1) 

10:34 0.12NS 7.9 ** 0.46NS 22.2** 

IT17K 939-1-1 × BB-POP-255-1 
(Pop 2) 

16:30 2.35NS 1.5NS 7.76* 10.0* 

APH-1-143 × APH-1-145 (Pop 3) 31:11:00 53.4** 15.4 ** 83.6 ** 17.2** 
  

     

**, : Significant deviation from model ratio at p<0.05), (p<0.01), ns: Non-significant 
deviation from model ratio; Obs: observed ratio. 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



33 
 

Table 7: Segregating pattern for pod twist in three F2 populations 

   X2 under different model ratios 
Crosses T:NT Ratio 3:1 9:7 13:3 27:37 
  Obs         

IT17K- 939-1-1  × IT17K-1267-2-1 2:42 9.8** 27.5NS 5.8** 25.6** 

IT17K 939-1-1  × BB-POP-255-1 6:40 3.5NS 17.2** 0.98NS 37.8** 

APH-1-143  × APH-1-145 24:18 23.1** 3.06NS 40.6** 3.9* 
 *, **: Significant and highly significant deviation from model ratio at p<0.05), (p<0.01), 
ns: Non significant deviation from model ratio; Obs: observed ratio. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



34 
 

4.1.5 Performance of F2 Progeny 

Table 8 shows the mean values for the F2  mean, parent 1 (P1 Mean), parent 2 mean, and 

the mid-parent value. In population 1 (IT17K- 939-1-1 × IT17K-1267-2-1), the pod 

shattering trait has an F2 Mean of 6.26, indicating the expression of the trait in the F2 

generation. The P1 Mean is 0.00, for the non-shattering parent. The P2 Mean is 55.00, 

which is the shattering parent showing a strong expression of the trait. The Mid Parent 

Mean is calculated at 27.50. For pod twist, it has an F2 mean of 0.47, P1 mean (non-twist 

parent) of 0.00, P2 mean (twist parent) of 21.00 and Mid parent mean of 10.50 

Population 2 (IT17K 939-1-1 × BB-POP-255-1) shows an F2 mean of 5.76, P1 mean of 

0.00, P2 mean of 46.30 and Mid parent values of 23.15 for the pod shattering trait. Whereas 

the pod twist trait showed an F2 mean value of 1.67, P1 mean value of 0.00, P2 mean value 

of 19.50 and a Mid parent value of 9.75 The F2 population 3 (APH-1-143  × APH-1-145 

F2), when tested for the  pod shattering trait showed an F2 mean value of 31.81,  P1 mean 

value of 0.00, P2 mean value of 100.00 and Mid parent value of 50.00. When tested against 

the  pod twist trait it showed F2 mean value of 20.20, P1 mean value of 0.00, P2 mean 

value of 100.00 and a Mid parent value of 50.00. 

4.1.6 Broad Sense Heritability Study 

The phenotypic variance of the F2 shows 135.68 for pod shattering and 4.67 for pod twist 

in population 1. Population 2 recorded 89.34 for pod shattering and 16.49 for pod twist. 

While Population 3 recorded 669.10 for pod shattering and 639.52 for pod twist. The 

variance of parent 1 records 0.00 for both pod shattering and pod twist across the three 

populations. The variance of parent 2 shows 50.00 and 2.00 for pod shattering and pod 

twist, respectively in population 1. Population 2 recorded 46.30 for pod shattering and  



35 
 

Table 8: Comparative Mean Values of Parental and F2 Generations for pod shattering 
and pod twist 
  Pop 1 Pop 2 Pop 3 

  Pdsht Pdtwst Pdsht Pdtwst Pdsht Pdtwst 

F2 Mean 6.26 0.47 5.76 1.67 31.81 20.2 

P1 Mean 0 0 0 0 0 0 

P2 Mean 55 21 46.3 19.5 100 100 

Mid parent 27.5 10.5 23.15 9.75 50 50 

AvPdsht(%) = pod shattering, Avpdtwst = pod twist, P1 = parent 1, P2 = Parent 2, pop 1 
= Population 1 (IT17K- 939-1-1 × IT17K-1267-2-1), Pop 2 = Population 2 (IT17K 939-
1-1 × BB-POP-255-1), Pop 3 = Population 3 (APH-1-143 × APH-1-145). 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 



36 
 

19.50 for pod twist. The variance of parent 2 for population 3 shows 0.00 for both pod 

shattering and pod twist. The environmental variance records 25.00 and 1.00 for pod 

shattering and pod twist in population 1. 23.15 and 9.75 are shown for pod shattering and 

pod twist, respectively in population 2. While population 3 recorded 0.00 for both pod 

shattering and pod twist. The genotypic variance for population 1 shows 110.68 for pod 

shattering and 3.67 for pod twist. Population 2 records values of 66.19 for pod shattering 

and 6.74 for pod twist. While, population 3 records 669.10 and 639.53 for pod shattering 

and pod twist, respectively.  

Broad sense heritability values for population 1 record 0.82 for pod shattering and 0.79 for 

pod twist. Population 2 shows 0.74 and 0.41 for pod shattering and pod twist respectively. 

Population 3 records 1.0 for both pod shattering and pod twist. The minimum value 

recorded for pod shattering and pod twist is 0.00 across the three populations. The 

maximum value obtained from the result for pod shattering and pod twist were 36.30 and 

10.50 respectively for population 1 (IT17K- 939-1-1 × IT17K-1267-2-). Population 2 

(IT17K 939-1-1 × BB-POP-255-1) recorded maximum values of 34.50 and 14.20 for pod 

shattering and pod twist respectively. Population 3 (APH-1-143 × APH-1-145) recorded 

100.00 as the maximum value for  pod shattering and  pod twist as shown in Table 9 

4.1.7. Traits Association 

The correlation analysis for all traits measured for pod shattering were analyzed and results 

presented in Figure 4.4, 4.5 and 4.6. The traits association analysis for population 1, as 

visualized in Figure 4.4, provides insights into the correlation between pod shattering and 

others traits measured in the research. 

Table 9: Broad sense heritability table of the F2 population for all three (3) crosses 



37 
 

  Pop 1 Pop 2 Pop 3 
 

AvPdsht Avpdtwst AvPdsht Avpdtwst AvPdsht Avpdtwst 

Min 0 0 0 0 0 0 

Max 36.3 10.5 34.5 14.2 100 100 

VF2 135.68 4.67 89.34 16.49 669.1 639.52 

Vp1 0 0 0 0 0 0 

VP2 50 2 46.3 19.5 0 0 

VE 25 1 23.15 9.75 0 0 

VG 110.68 3.67 66.19 6.74 669.1 639.52 

H2 0.82 0.79 0.74 0.41 1 1 

AvPdsht(%)=  pod shattering, Avpdtwst = pod twist, P1 = parent 1, P2 = Parent 2, Min = 
minimum, Max = Maximum, VG = Genotypic variance, VE = Environmental variance, 
VP1 = ?, VP2 = ?, VF2 =? H2 = Broad sense heritability, pop 1 = Population 1 (IT17K- 
939-1-1 × IT17K-1267-2-1), Pop 2 = Population 2 (IT17K 939-1-1 × BB-POP-255-1), 
Pop 3 = Population 3 (APH-1-143 × APH-1-145). 

 

 

 

 

 

 



38 
 

Figure 4.4: Pairwise correlation plot for population 1  



39 
 

Pod twist trait exhibited a moderate positive and significant correlation with pod shattering 

(r = 0.437), similarly, twist number showed a positive correlation with pod shattering (r = 

0.275). 

Twist number also showed a nearly perfect correlation with pod twist (r = 0.991). Pod 

number and pods per peduncle showed weak positive correlations with pod shattering (r = 

0.190 and r = 0.251, respectively). Seed weights also had a weak correlation (r = 0.207). 

Days to 50% flowering, days to full pod maturity, and days to 90% pod maturity all 

demonstrated negligible and non-significant correlations with pod shattering (r ranging 

from -0.040 to +0.038). 

The trait association analysis in population 2 as shown in Figure 4.5 reveals the following 

correlation with pod shattering. Pod Twist exhibits a strong positive correlation with pod 

shattering (r = 0.87). Twist Number also shows a strong positive correlation (r = 0.82) with 

pod shattering. Pod number showed a moderate negative correlation with pod shattering (r 

= -0.31). Other traits such as days to flowering, days to pod maturity, pod length, and seed 

weight show weak or negligible correlation with pod shattering. 

In population 3 as shown in Figure 4.6, Pod Twist shows a strong positive correlation with 

pod shattering (r = 0.85). Twist number as well shows a strong positive correlation with 

pod shattering (r = 0.88). Pod Length displays a moderate positive correlation with pod 

shattering (r = 0.58). Pod number shows a weak negative correlation (r = -0.17) with pod 

shattering. Other traits like seed weight and flowering/maturity periods remain weakly or 

non-significantly correlated to pod shattering. 



40 
 

 

Figure 4.5: Pairwise correlation plot for population 2 



41 
 

 

Figure 4.6: Pairwise correlation plot for population 3 



42 
 

4.1.8. Phenotypic, Genotypic, and Environmental Correlations of Pod Shattering 

The phenotypic, genotypic, and environmental correlations of pod shattering with other 

agronomic and physiological traits were evaluated in the three populations (Figure 4.7). 

Phenotypic correlation 

Phenotypic correlations between pod shattering and other traits showed a strong positive 

association with pod twist and seed weight across the three populations. Population 3 

recorded the highest correlation between pod shattering and pod twist (r = 0.99), while 

population 2 and population 1 showed similarly high values (r = 0.91 and r = 0.89, 

respectively). Likewise, seed weight also correlated strongly with pod shattering (r = 0.87, 

0.80, and 0.60 for populations 3, 2, and 1, respectively). In contrast, days to 50% flowering, 

days to pod maturity, and days to 95% pod maturity showed weak to negligible correlations 

with pod shattering (ranging from -0.20 and 0.20), suggesting limited phenotypic 

association with pod shattering tendency. 

Genotypic correlation 

In the genotypic correlation analysis, pod twist exhibited the strongest positive genotypic 

correlation with pod shattering in all three populations, with coefficients of r = 0.94 (pop 

1), r = 0.96 (pop 2), and r = 1.00 (pop 3). Seed weight and twist number also displayed 

moderately high genotypic correlations with pod shattering (r = 0.85 for seed weight in pop 

2 and r = 0.67 in pop 1). 

Environmental correlation 

Environmental correlations were generally lower in magnitude compared to genotypic 

correlations, but still significant for specific traits. Pod twist retained a high environmental 

correlation with pod shattering (r = 0.98 in pop 3). Seed weight and twist number similarly 

demonstrated notable environmental associations. 



43 
 

 

 

Figure 4.7: Phenotypic, genotypic, and environmental correlations  



44 
 

4.2 DISCUSSION 

4.2.1 Parental Screening and Selection. 

The significant variation indicates that the screened genotypes differ substantially in their 

susceptibility to pod shattering, providing an opportunity for selection of shattering-

resistant lines. Lines with low pod shattering can be advanced for further breeding or used 

in crosses to introduce this desirable trait into other backgrounds. Similarly, the highly 

significant difference in pod twisting suggests that this trait is also genetically controlled 

and genes can be introgressed into other genotypes to reduce twisting, which may influence 

shattering resistance. Aph -1-141, Aph-1-143 and Danila happen to be the most shatter-

resistant lines tested. They showed other desirable traits like early flowering and maturity, 

moderate pod girth and pod length. These lines can be utilized in breeding program to 

develop ideal genotypes. These findings are consistent with previous research that 

identified pod shattering as a key trait in cowpea improvement programs, particularly for 

enhancing seed retention and reducing post-harvest losses (Kumar et al., 2019). The ability 

to select for both non-shattering and shattering-prone lines within the population supports 

the hypothesis that pod shattering is genetically variable and can be manipulated through 

breeding (Li et al., 2017). 

4.2.2 Frequency Distribution of Phenotypic Data for Pod Shattering and Pod Twists 

The frequency distribution analysis revealed that pod shattering and pod twisting traits 

across all studied cowpea populations exhibited a highly skewed pattern with entities 

showing classical grouping. This deviation from a typical normal distribution suggests that 

variation in pod shattering is likely controlled by a single or a few major genes, as opposed 

to polygenic inheritance. Similar observations have been reported in studies examining the 



45 
 

inheritance of pod shattering in other leguminous crops. Some contrasting outcomes, 

however, have been documented by other workers. Pickett et al. (2007), argued that pod 

shattering in Arabidopsis involves a more complex interplay of genetic and environmental 

factors, with numerous loci contributing small additive effects.  

Similarly, Obi et al. (2018), believed that a few loci play a major role, the segregation 

patterns in certain populations could be influenced by modifier genes or epistatic 

interactions, leading to quantitative inheritance patterns in specific cowpea genetic 

backgrounds. These differences in findings underscore the influence of genetic 

architecture, environmental factors, and methodological approaches in understanding the 

inheritance of pod shattering. Further molecular analyses, such as QTL mapping or gene 

expression studies, are necessary to identify and confirm the underlying genes responsible 

for pod shattering in cowpea and other legumes. 

4.2.3. F2 Segregation Pattern for Pod Shattering 

The F2 segregating population for pod shattering exhibited diverse inheritance patterns, 

indicative of varying genetic mechanisms underlying this trait. In Population 1, pod 

shattering was recessive, resulting in a non-shattering phenotype. The observed segregation 

ratios of 3:1 and 13:3 suggest a genetic mechanism that involves both single-gene 

dominance and dominant inhibitory epistasis involving two genes interacting together, 

where a dominant allele at one locus inhibits the expression of another dominant allele at 

another locus. These findings align with previous studies, such as those by Lo et al. (2021), 

who identified key genomic regions in cowpea, including Vigun03g321100 and 

Vigun11g100600, that influence pod shattering through their role in cell wall biosynthesis. 



46 
 

Such interactions underscore the complexity of this trait, particularly in legumes where 

both major and minor genes influence the same trait. 

Similarly, Population 2 exhibited recessive inheritance of pod shattering, also expressing a 

non-shattering phenotype. The inheritance ratios of 3:1 and 9:7 highlight a blend of single-

gene dominance and complementary gene action. The 9:7 ratio specifically points to 

epistatic interactions between two loci, where both genes appear to suppress the shattering 

trait. This genetic interplay has been observed in prior research on legumes, including 

Mohammed et al. (2009), who documented the role of multiple genes in modulating pod 

shattering. The involvement of complementary gene action in this population underscores 

the importance of gene-gene interactions in trait expression, further demonstrating the 

genetic complexity underlying this key agronomic characteristic. 

Population 3 showed a dominant expression of pod shattering, producing a shattering 

phenotype. The observed segregation ratios in this population diverged from classical 

Mendelian ratios, suggesting a multifactorial inheritance pattern. This implies that several 

loci, possibly involving both major and minor genes, interact to regulate the shattering trait. 

Similar complexities have been noted in common beans in which a major regulatory gene 

PvMYB26 was found to interact with additional loci to influence pod dehiscence (Rau et 

al., 2019). The dominant expression of pod shattering in this population highlights the 

genetic diversity within cowpea and the role of multiple interacting loci in it control. 

4.2.4. F2 Segregating Pattern for Pod Twist 

The inheritance of pod twist followed comparable patterns of genetic complexity across 

the populations. In Population 1, pod twist was recessive, leading to a non-twisting 

phenotype. The observed 9:7 ratio indicates complementary gene interactions, where two 



47 
 

genes act together to express the twisting trait. This finding is consistent with earlier studies 

by Brick et al. (1993), who observed similar complementary interactions in the inheritance 

of twisted pods in common beans. The recessive nature of the trait in this population 

suggests that the absence of dominant alleles at specific loci is necessary for the non-

twisting phenotype to manifest. 

For Population 2, pod twist was also recessive, producing a non-twisting phenotype. The 

inheritance pattern of 3:1 reflects simple Mendelian dominance/recessive monohybrid 

system at play, although epistatic interactions may have played a role in modifying the trait 

expression. This dual pattern aligns with the findings of Dong et al. (2014), who described 

the influence of both single-gene dominance and epistatic interactions in soybean pod 

traits. The interplay of these genetic factors demonstrates the nuanced regulation of pod 

twist in this population. 

In Population 3, pod twist was dominantly inherited, resulting in a twisting phenotype. The 

observed 9:7 ratio indicates complementary gene action, where two dominant alleles at 

separate loci contribute to the expression of the trait. These results support the work of 

Parker et al. (2020), who highlighted the involvement of both major-effect loci and minor 

modifiers in traits related to pod deformation. The dominant inheritance of pod twist in this 

population emphasizes the role of genetic diversity in shaping pod-related traits across 

cowpea populations. 

4.2.5. Mean Performance of the F2 and Parents 

In population 1 the F2 mean for pod shattering is much lower than the mid parent value. 

This suggests that the F2 generation had less pod shattering and dominance gene action 

plays a critical role in the inheritance of the trait. Dominant alleles from one parent may be 



48 
 

masking the expression of recessive alleles in the other, leading to reduced trait expression 

in the F2 population. Similarly, the F2 Mean for pod twist was lower than the mid parent 

suggesting the preponderance of non-additive gene controlling the trait. Kataliko et al. 

(2018) reported greater influence of non-additive gene in the inheritance of pod shattering 

in soybeans. Funatsuki et al. (2014) reported similar dominance effect which loss-of-

function alleles in pod dehiscence-related genes exhibit recessive inheritance patterns in 

soybean. These support the idea that dominant alleles mask the expression of recessive 

alleles, leading to reduced trait expression in F2 populations. 

In population 2, the lower F2 Mean for pod shattering compared to the mid parent strongly 

suggest recessive control. Pod twist mean was also lower than the mid parent similarly 

suggesting recessively inheritance. A dominant epistatic interaction is suspected here, a 

single locus effect and a non-additive gene action. Patel et al., (2021) found that non-

additive gene action was predominant for most traits, including pod twist aligning with the 

observation of non-additive gene action for pod twist in this result. Previous report in 

legumes suggests that pod twisting is influenced by genes regulating cell wall integrity, 

and their dominance interactions can suppress excessive twisting (Suanum et al., 2016).  

In population 3, F2 mean for pod shattering was significantly lower than the P2 Mean but 

higher than the mid parent. This could suggest a more complex inheritance pattern, possibly 

with partial dominance or multiple genes influencing the trait. F2 Mean for the  pod twist 

was closer to the Mid Parent value but lower, indicating the trait might be influenced by 

both additive and non-additive genetic factors. Isemura et al., (2012) reported similar 

observations in mung bean, where pod shattering resistance was partially controlled by 

both major QTLs and polygenic factors. 



49 
 

4.2.6 Broad Sense Heritability  

Heritability for pod shattering, indicate that genetic factors play a major role in the 

expression of this trait. The high broad-sense heritability (H²) suggests that a large 

proportion of the observed phenotypic variation in pod shattering is due to genetic variance, 

making this trait highly heritable and amendable to selection for improvement. Similar 

findings have been reported by Murgia et al. (2017), who documented high heritability 

estimates for pod shattering in legumes, supporting the findings of this study. Additionally, 

Li et al. (2019) reported heritability estimates ranging from 0.70 to 0.95 in cowpea, further 

reinforcing the genetic control of this trait. 

The heritability variation in pod twist suggests that while genetic factors contribute 

significantly to pod twist, environmental influences also play a role in its expression, 

particularly in populations with lower heritability values. Moderate heritability implies that 

selection may be less efficient in improving this trait compared to pod shattering. Reports 

from Zhang et al. (2021) found heritability for pod twist in cowpea to range from 0.50 to 

0.88, which aligns with the findings of the present study. Similarly, Silva et al. (2020) 

observed heritability estimates of approximately 0.79 for pod twist, further supporting the 

genetic basis of the trait. 

These findings indicate that pod shattering exhibits higher genetic control than pod twist, 

making it a more suitable candidate for genetic improvement through breeding. However, 

despite the moderate heritability observed for pod twist in some cases, selection for reduced 

pod twisting remains feasible, especially in environments with controlled conditions to 

minimize environmental variance. This information is valuable for breeders aiming to 



50 
 

develop cowpea varieties with reduced pod shattering and pod twist, ultimately improving 

yield stability and post-harvest handling. 

4.2.7 Character Association 

In all three populations, pod twist and twist number consistently exhibited strong and 

significant positive correlations with pod shattering, most notably in Population 2. These 

findings underscore the mechanical role of pod valve tension in the shattering process. 

Twisting tension builds up during pod drying, and once structural limits are exceeded, the 

pod dehisces explosively (Mabrouk et al., 2018; Dong et al., 2014). These results suggest 

that pod twist and twist number are the most reliable and consistently associated traits with 

pod shattering in cowpea and can be used for early-generation screening. Their strong 

positive correlations across diverse populations validate their role in the mechanism of 

shattering, making them ideal targets for phenotypic selection or potential QTL mapping. 

The near perfect correlation between pod twist and twist number in Population 1, suggests 

that these traits are genetically and developmentally linked, and could serve as early 

phenotypic indicators for susceptibility to shattering. This is similar to reports by Lo et al. 

(2018), who found similar strong relationships between pod coiling and dehiscence in 

cowpea and its wild relatives. 

Pod length, which showed a moderate positive correlation with pod shattering in 

Population 3, but a negligible association in Population 2, presents a complex relationship, 

suggesting that longer pods may, in some cases, enhance shattering due to greater 

mechanical stress along the suture line. However, literature offers conflicting 

interpretations. Suanum et al. (2016) proposed that longer pods may sometimes delay 

shattering due to more gradual moisture loss and tension release. Hence, this relationship 



51 
 

may be environment and genotype-dependent, necessitating further multi-location 

validation. 

The number of pods showed a moderate to weak negative correlation. This may suggest a 

trade-off mechanism where plants investing more in pod quantity may allocate fewer 

resources to structural features like twist formation or lignification, potentially reducing 

shattering tendency. However, the weak or inconsistent correlations caution against relying 

solely on this trait for indirect selection. 

Seed weight had weak positive correlations across the three populations, indicating that 

heavier seeds may marginally contribute to internal tension in the pod, but this relationship 

is not significant enough to be a primary selection trait. This finding supports the results of 

Masha et al. (2021), who observed no strong linkage between seed mass and pod shattering 

in segregating cowpea populations. Similarly, traits such as days to 50% flowering, days 

to pod maturity, and days to 90% maturity displayed negligible and non-significant 

correlations with pod shattering in all populations. This confirms that phenological 

development is largely independent of shattering susceptibility in cowpea under the studied 

conditions. Hence, these traits may not be effective for indirect selection in shattering 

resistance breeding. 

The observed variation across populations also emphasizes the quantitative and possibly 

polygenic nature of pod shattering inheritance. Integrating morphological trait selection 

with molecular tools such as genome-wide association studies (GWAS) or marker-assisted 

selection could help identify stable genomic regions conferring resistance to pod shattering 

(Lo et al., 2018; Suanum et al., 2016). 



52 
 

The genotypic correlations mirrored the phenotypic trends, however, with stronger 

coefficients, indicating that the observed trait associations are under genetic control. Pod 

twist maintained the strongest genotypic association with pod shattering in all three 

populations, emphasizing its potential as a genetically linked trait. Such strong correlations 

imply pleiotropy or tight linkage between the genes governing twist and shattering 

behavior, an assertion supported by QTL mapping studies in soybean and common bean 

(Dong et al., 2014; Parker et al., 2020). 

Seed weight and twist number also displayed moderate to high genotypic correlations with 

pod shattering. As seen in population 1 and 2. The trait "twist number," which quantifies 

the degree of helical deformation in shattering pods, has previously been shown to correlate 

with dehiscence intensity (Ogbonna et al., 2021). These findings suggest that both traits 

may serve as secondary selection indices in early-generation breeding when direct 

shattering assessment is impractical. 

Environmental correlations, though generally lower than genotypic associations, were still 

appreciable, particularly between pod twist and pod shattering. This suggests that 

environmental conditions such as humidity and temperature at maturity may influence pod 

twisting and thus indirectly affect shattering. Similar observations have been made in 

soybean, where high environmental humidity delayed pod drying and reduced shattering 

incidence (Tiwari & Bhatia, 2014). These findings underscore the importance of 

standardizing environmental conditions or adjusting for them when screening genotypes 

for shattering resistance. 

 



53 
 

 

 

 

 

 

 

 

 

 

 

 Formatted: Centered



54 
 

CHAPTER FIVE 

5.0 SUMMARY, CONCLUSION, AND RECOMMENDATIONS 

5.1 SUMMARY 

A study was conducted to evaluate the level of variation in pod shattering among advanced 

cowpea breeding lines and the inheritance pattern of resistance to pod shattering in cowpea. 

The experiment was conducted at the International Institute of Tropical Agriculture (IITA) 

Kano, Screen House, and at its research station in Minjibir. The research study began with 

the screening of 36 cowpea lines including advanced breeding lines and a wild relative 

under rainfed conditions at the IITA research station in Minjibir. All 36 advanced cowpea 

genotypes including a wild relative were evaluated in a field condition from July to October 

2022. The experimental design employed was a 6×6 Alpha Lattice design with two 

replications, two rows per plot, each row measuring 2m and 1m spacing between plots. 

Seeding rate of 2 per hill, 20 hills per plot, and a supposed optimum of 40 plant stands per 

plot. 

The result obtained from parental screening led to the selection of 6 parental lines APh-1-

145, IT17K-1267-2-1, and BB-S-POP2-255-2 as shattering (male) lines for the crosses 

while IT17K-939-1-1, IT17K-2024-7, and Aph-1-143 were selected as non-shattering 

(female) lines.  These were hybridized in the screen house to create 3 F1 populations using 

a bi-parental mating design. The 3 F1 populations generated from the parental crosses were 

grown in the screen house. Five pots were used for each population. This phase was 

accomplished from October 2022 to January 2023 to get the F2 population. Evaluation of 

the F2 population was carried out in the field in July 2023 under rainfed conditions. The 

experimental design used was a Randomized Complete Block Design (RCBD) with two 



55 
 

replications/blocks. Each population was evaluated separately for segregation and 

variation. Agronomic and phenotypic data were collected through the vegetative and 

reproductive phases of the crop, and pod shattering data were taken at pod maturity.  

Data obtained was subjected to ANOVA for pod shattering by deriving the mean square of 

all 36 parental lines in the analysis of variance for all traits measured in the parental 

screening using R Studio analytics software. Data obtained from the segregating F2 

populations was analyzed using Microsoft Excel for the frequency distribution of pod 

shattering and pod twist, determine the segregating pattern of the F2 populations, mean 

performance of the F2 and parents for pod shattering and pod twist, analyzed the broad 

sense heritability, and character association for pod shattering. 

The frequency distribution of the phenotypic data for pod shattering and pod twisting 

shows a distribution pattern that favors major gene inheritance in the F2 generation for 

populations 1 and 2. While Population 3 had implied multiples gene action as a prerequisite 

for inheritance of the traits. The F2 segregating population for population 1 (IT17K- 939-

1-1 × IT17K-1267-2-1) showed an inheritance that favors the 3:1 and 13:3 inheritance 

ratios suggesting that the inheritance is controlled by a single gene and also indicates the 

presence of epistatic action. Population 2 (IT17K 939-1-1 × BB-POP-255-1 F2) 

segregation suggests that pod shattering inheritance is controlled by a single gene and also 

shows the possibility of inheritance being controlled by two genes interacting in a 

complimentary manner. Population 3 (APH-1-143 × APH-1-145) has shown a significant 

difference from the inheritance ratio tested; however, it is also been tested for pod twist. 

The segregating pattern for pod twist showed a complementary gene action as a 

prerequisite for the trait’s inheritance in population 1 (IT17K- 939-1-1 × IT17K-1267-2-1) 



56 
 

favoring a 9:7 inheritance ratio.  Population 2 (IT17K 939-1-1 × BB-POP-255-1) 

segregation suggests a single gene inheritance and an epistatic interaction in the inheritance 

of the trait. Population 3 (APH-1-143 × APH-1-145) segregating population suggests an 

inheritance caused by two genes in a complementary interaction, favoring a 9:7 inheritance 

ratio. The comparative mean study for the 3 populations showed that the variation in F2 

Means across the traits indicates that the inheritance patterns differ, and multiple genetic 

factors could be at play. The data suggests that breeding for reduced pod shattering and 

twist might require selection against the recessive alleles responsible for these traits. 

Broad-sense heritability (H2) for pod shattering in population 1, suggests that 82% of the 

phenotypic variance is due to genetic variance, 79% for pod twist. In population 2, the H2 

for pod shattering suggests 74% of the phenotypic variance in pod shattering can be 

attributed to genetic factors in this population. For pod twist, the H2 indicates that 41% of 

the phenotypic variance in pod twist is due to genetic factors, suggesting a greater influence 

of environmental factors on this trait. Broad-sense heritability in population 3 showed a 

100% heritability for both traits, meaning that all observed variance is due to genetic 

factors. The character association studies indicates that the pod twist trait is strongly 

correlated with pod shattering across all three populations followed by twist number. 

5.2 CONCLUSION 

This study further reinforces other studies that have earlier been conducted reaffirming that 

pod shattering is a heritable trait. The pod shattering trait showed high genetic variance and 

heritability. The study also showed that the inheritance of pod shattering was controlled by 

single and multiple genes that were influenced by epistasis in a complementary and 

dominant manner. Epistatic interactions between major and minor genes significantly 



57 
 

impact the inheritance of shattering resistance. The study further suggests that pod 

shattering and pod twist are closely correlated and can be studied together in a bid to further 

understand the inheritance of pod shattering in cowpea. 

5.3 RECOMMENDATIONS 

From the findings obtained from this research, from both statistical results and empirical 

field experience, the following recommendations are hereby presented. 

1. Breeding lines exhibiting low pod shattering levels should be prioritized for further 

advancement and hybridization, given the significant variation observed among 

advanced cowpea lines, which indicates the availability of exploitable genetic 

diversity for improving shattering resistance.  

1.2.Breeding strategies should prioritize selection against recessive alleles associated 

with pod shattering and pod twist, as the segregation patterns and mean 

performance of the F₂ populations indicate that these alleles contribute significantly 

to susceptibility, particularly under complementary and epistatic gene interactions. 

2.3.Pod twist and twist number should be incorporated as primary selection criteria in 

cowpea breeding programmes targeting resistance to pod shattering, as their strong 

and consistent phenotypic and genotypic associations with pod shattering across 

populations make them reliable indicators for early-generation screening. 

3. Breeding strategies should prioritize selection against recessive alleles associated 

with pod shattering and pod twist, as the segregation patterns and mean 

performance of the F₂ populations indicate that these alleles contribute significantly 

to susceptibility, particularly under complementary and epistatic gene interactions. 

  

Formatted: Font: (Default) Times New Roman, 12 pt

Formatted: Numbered + Level: 1 + Numbering Style: 1, 2,
3, … + Start at: 1 + Alignment: Left + Aligned at:  0.25" +
Indent at:  0.5"



58 
 

 
 
 

4.  

REFERENCES 

Allorent, M., Rojas, A., & Diop, N. N. (2021). Characterization of pod wall and suture 
structures linked to shattering resistance in cowpea. Plant Science, 311, 110996. 
https://doi.org/10.1016/j.plantsci.2021.110996 

Ambrose, S. and Ellis, R. H. (2008). The evolution of ballistic seed dispersal in legumes. 
New Phytologist, 178(1), 1–15. 

Andargie, M., Pasquet, R. S., Gowda, B. S., Muluvi, G. M. and Timko, M. P. (2014). 
Molecular mapping of QTLs for domestication-related traits in cowpea (V. 
unguiculata (L.) Walp.). Euphytica, 200, 401–412. 

Bandillo, N., Raghavan, C., Muyco, P. A., Sevilla, M. A. L., Lobina, I. T., Dilla-Ermita, 
C. J., ... McCouch, S. (2017). Multi-parent advanced generation inter-cross 
(MAGIC) populations in rice: Progress and potential for genetics research and 
breeding. Rice, 10(1), 1–15. 

Boukar, O., Belko, N., Chamarthi, S., Togola, A. and Batieno, J. (2019). Cowpea (Vigna 
unguiculata): Genetics, genomics and breeding. Plant Breeding, 138(4), 415–424. 

Boukar, O., Belko, N., Chamarthi, S., Togola, A., Batieno, J., Owusu, E. Y., Haruna, M., 
Diallo, S., Umar, M. L. and Fatokun, C. (2019). Cowpea (Vigna unguiculata): 
Genetics, genomics and breeding. Plant Breeding, 138(4), 415–424. 
https://doi.org/10.1111/pbr.12589 

Boukar, O., Fatokun, C. A., Huynh, B. L., Roberts, P. A. and Close, T. J. (2018). Genomic 
tools in cowpea breeding programs: Status and perspectives. Frontiers in Plant 
Science, 9, 134. https://doi.org/10.3389/fpls.2018.00134 

Boukar, O., Fatokun, C. A., Huynh, B.-L., Roberts, P. A. and Close, T. J. (2016). Genomic 
tools in cowpea breeding programs: Status and perspectives. Frontiers in Plant 
Science, 7, 757. https://doi.org/10.3389/fpls.2016.00757 

Boukar, O., Fatokun, C. A., Roberts, P. A., Abberton, M. T., Huynh, B. L., Close, T. J., 
Kyei-Boahen, S. and Higgins, T. J. V. (2015). Cowpea. In Genetic improvement of 
tropical crops (pp. 219–250). Springer. https://doi.org/10.1007/978-1-4939-2797-
5_7 

Formatted: List Paragraph, Left, Line spacing:  single

Formatted: List Paragraph, Justified, Numbered + Level: 1
+ Numbering Style: 1, 2, 3, … + Start at: 1 + Alignment: Left
+ Aligned at:  0.25" + Indent at:  0.5"

https://doi.org/10.1016/j.plantsci.2021.110996
https://doi.org/10.1111/pbr.12589
https://doi.org/10.3389/fpls.2016.00757
https://doi.org/10.1007/978-1-4939-2797-5_7
https://doi.org/10.1007/978-1-4939-2797-5_7


59 
 

Boukar, O., L. M. T. (2015). Genotype by environment interaction for yield and agronomic 
traits in cowpea. Agricultural Sciences, 6(3), 215–220. 
https://doi.org/10.4236/as.2015.63021 

Daneji, M. U., Chikoye, D. and Hussaini, M. A. (2016). Pod shattering in cowpea: Genetic 
control, impact, and utilization in breeding. Crop Science, 56(1), 1–12. 

Diop, N. N., Odeny, D. A. and Orobiyi, A. (2015). Genetic mapping of pod shattering in 
cowpea (Vigna unguiculata L. Walp). Genetics and Molecular Research, 14(3), 
9860–9870. https://doi.org/10.4238/2015.September.30.2 

Dong, Y., Wang, F., Wu, J. and Liu, Y. (2014). Identification of pod shattering-related 
traits in cowpea (Vigna unguiculata) using QTL analysis. Frontiers in Plant 
Science, 5, 596. https://doi.org/10.3389/fpls.2014.00596 

Dong, Y., Yang, X., Liu, J., Wang, B. H., Liu, B. L., Wang, Y. Z. and Qiu, L. J. (2014). 
Pod shattering resistance associated with domestication is mediated by a NAC gene 
in soybean. Nature Communications, 5, 3352. https://doi.org/10.1038/ 
ncomms4352 

Dong, Y., Yang, X., Liu, J., Wang, B. H., Liu, B. L., Wang, Y. Z. and QTL mapping and 
gene discovery of shattering resistance in soybean. Molecular Breeding, 33(3), 
557–567. 

Dutta, S., Kumari, K., Singh, B., Sarker, A. and Reddy, K. R. (2019). Pod dehiscence in 
cowpea: A review. Frontiers in Plant Science, 10, 1–14. 

Ehlers, J. D., Hall, A. E. and Tenkouano, A. (2000). Mapping of quantitative trait loci 
associated with pod shattering in cowpea [Vigna unguiculata (L.) Walp]. 
Euphytica, 112(2), 145–150. https://doi.org/10.1023/A:1003891501303 

Fang, Y., Xu, H., Wei, X., Wang, J., Yu, D. and Wang, Y. (2014). Identification and 
expression analysis of lignin biosynthesis-related genes in cowpea (Vigna 
unguiculata) during pod shattering. BMC Plant Biology, 14, 110. 
https://doi.org/10.1186/1471-2229-14-110 

FAO. (2017). FAO-statistics. Food and Agriculture Organization. 
http://apps.fao.org/dataset?entryId=29920434-c74e-4ea2-beed-01b832e60609 

FAO. (2023). FAOSTAT statistical database. Food and Agriculture Organization of the 
United Nations. https://www.fao.org/faostat 

Fatokun, C. A., Ng, N. Q., Boukar, O. and Kamara, A. Y. (2018). Identification of QTLs 
associated with pod shattering resistance in cowpea (Vigna unguiculata L. Walp.) 
using QTL-seq analysis. BMC Genomics, 19(1), 1–13. 

https://doi.org/10.4236/as.2015.63021
https://doi.org/10.4238/2015.September.30.2
https://doi.org/10.3389/fpls.2014.00596
https://doi.org/10.1038/%20ncomms4352
https://doi.org/10.1038/%20ncomms4352
https://doi.org/10.1023/A:1003891501303
https://doi.org/10.1186/1471-2229-1