Genetic analysis of resistance to Radopholus similis in Banana

Abstract

Banana is an important crop worldwide mostly grown in tropical and subtropical regions, of annual production is 145 million metric tons valued at 26.5 billion Euros. Banana production is threatened by various constraints including pests and diseases. Among the pests, Radopholus similis is the most destructive species. East African Highland Bananas mostly grown in Uganda and other parts of East Africa are highly susceptible to this species with yield reduction reaching 80%. Breeding for resistance is the only sustainable way of controlling this pest. Unfortunately, banana breeding is limited by many factors where long cycle is among the important ones. Heritability and mode of inheritance are key elements in determining the appropriate breeding approach and strategy, and interventions aiming at speeding up the breeding cycle for this crop are highly needed. The aim of this study was to understand the inheritance pattern of resistance to R. similis and determine genomic regions in the banana genome which are responsible for that resistance. The study was conducted in IITA-Uganda in 2017 and 2018 using a multi parent population produced from crosses between two types of Zebrina GF (susceptible) and Calcutta 4 (resistant) with the two Zebrina GF used as male and Calcutta 4 as female. Yangambi Km5 was used as a resistant control, while Valery was used as susceptible control. The study was conducted in 7 series and genotypes were arranged in randomized complete block design. The single-root nematode screening method was used, and data were collected on total nematodes count and root damage as necrosis. The final nematode population of each genotype was compared with the final nematode population of each of the controls. The analysis of variance using Genstat 19th edition showed a significant variation of the genotypes for total nematodes count and necrosis damage. The traits had moderate heritability of 56% and 43% (for nematode reproduction necrosis damage respectively) and they were positively correlated (r= 0.48). Out of 104 genotypes screened, 11 were resistant, 39 partially resistant, 54 susceptible. The resistant and partial resistant hybrids from this study can be used as source of resistance in banana breeding after being evaluated for other important traits. For the QTLs identification, the same material highlighted above was genotyped using Diversity Array Technology – sequencing (DArTSeq) platform that generated 88,947 SNPs. Genstat 19th edition was used to run the QTL analysis for the two traits with a total of 21,266 filtered SNPs. The analysis revealed 7 putative QTLs associated with Radopholus similis in banana located on chromosomes 1, 2, 3 4 and 9. These QTLs, after validation, will be useful in marker-aided improvement of banana resistance to nematodes especially in shortening breeding cycles