Soybean [Glycine max (l.) Merrill] germplasm evaluation for agronomic and seed composition traits in Rwanda.

Soybean [Glycine max (L.) Merr.] is a valuable crop worldwide. Soybean protein meal and oil can be used in human diet or livestock feed and are crucial in determining the value of the soybean crop. Soybean has been included in the Government of Rwanda Crop intensification Program (CIP). However, soybean production in Rwanda is low and does not meet local demand because of lack of high yielding varieties. There is a need to develop high yielding cultivars that are adapted to the Rwandan environment of short day, high elevation, cool temperatures, however little is known about which germplasm to grow in Rwanda. The objectives of this research were to evaluate the adaptability and stability of a collection of 466 G. max accessions, sourced from the United States Department of Agriculture National Genetic Resources Program (GRIN) that were collected from the USA, China, Japan, Russia, South Korea, and other countries, in the Rwanda soybean growing environment. Another objective was to conduct a genome wide association study for agronomic and seed composition traits. Using a randomized complete block design with three replications in three environments (2017A, 2017B, 2018A), field tests were conducted in Bugesera. For the 2018B season, tests were grown in three locations; Bugesera, Nyagatare and Rubona with two replications for a total of six environments. The phenotypic data collected included days to flowering (R1), beginning pod date (R3), maturity date (R8), reproductive period (RP; R8-R1), reproductive period from beginning pod (RP_3; R8-R3), plant height, 100 seed weight, single row plot yield, seed protein and amino acids, seed oil and fatty acids. Analyzing the data from the six environments, we found genotype and genotype by environment were significant (p < 0.001) sources of variation for days to flowering (R1), beginning pod date (R3), maturity date (R8), reproductive period (RP; R8-R1), reproductive period from beginning pod (RP_3; R8-R3), plant height, 100 seed weight, single row plot yield, seed protein and amino acids, seed oil and fatty acids. Significant correlations were observed between numerous traits. An additive main effects and multiplicative interaction (AMMI) and genotype plus genotype-by-environment (GGE) biplot analyses were conducted on maturity and yield data of a subset of 62 genotypes in a multi-location yield trial which was conducted over three test environments in Rwanda in 2019 in a randomized complete block design with three replications. In addition, a genome wide association analysis revealed 329 quantitative trait nucleotides (QTNs) that were significantly associated with R1, R3, maturity, reproductive period and reproductive period from beginning pod, seed weight, plant height, seed protein and oil. The results of this study suggests that adaptation to the Rwandan environment and/or similar environments may be regulated by the complex interaction of multiple genes and associations other than those that have previously been reported. The information and data collected in this study will be invaluable in guiding soybean breeders and geneticists in selecting promising soybean accessions for research and cultivar improvement for the Rwandan environment.