Grain yields of rust resistant promiscuous soybean lines in the Guinea savanna of Nigeria

Abstract

Soybean rust, caused by Phakopsora pachyrhizi, has become a threat to soybean production in west, central, east and southern Africa. This foliar disease can cause 40-80% yield loss under African conditions. IITA started to develop resistant lines for this disease since 2003 and a number of homozygous lines from the breeding program have reached line evaluation stage. Seventeen F8 rust resistant lines derived from the cross TGx 1805-31F (rust susceptible elite line) with UG 5 (rust resistant line), together with three checks, were evaluated at five locations in Nigeria during the 2008 main growing season. The experiment was laid out in a randomized complete block design with four replications at Ibadan, Mokwa, Zaria, Kano and Book. Analysis of variance was carried out using PROC MIXED. Lines showed significant difference for grain yield at all locations except at Zaria. Combined analysis of variance over the five locations also showed highly significant differences. Seven lines gave significantly higher yields compared to the standard variety TGx 1485-1D. The mean yield of these lines ranged from 1951-2241 kg ha-1, whilst TGx 1485-1D yielded 1699 kg ha-1. The other standard check variety TGx 1019-2EN, which gave 1764 kg ha-1, was also significantly outperformed by five lines. Line × location interaction was significant for grain yield which indicated changes in rank order of lines in different locations. Lines also differed significantly for fodder yield. The highest mean fodder yield of 2475 kg ha-1 was obtained from the standard variety TGx 1485-1D, but nine test lines gave a comparable fodder yield by being not significantly different from the check. Difference for mean 100-seed weight was also significant and 10 test lines gave large seeds (14-17 g) as compared to the checks (12-13 g). Of the test lines, TGx 1987-9F, TGx 1987-10F and TGx 1987-23F had relatively bigger seeds (16-18 g). In addition, the test lines also showed good nodulation, resistance to frogeye, bacterial pustule, pod shattering and lodging. All the lines matured on average in 89-97 days. Thus, three superior lines TGx 1987-62F, TGx 1987-10F and TGx 1987-9F will be considered for on-farm trials to expedite their release in Nigeria. Moreover, these lines would be of a great value to different parts of Africa where rust has become a limiting factor in soybean production.