Soybean genetic diversity and resistance to soybean rust disease

This study was conducted to enhance breeding for resistance to soybean rust, the greatest obstacle to soybean production in Uganda. To undertake this assignment, 91 exotic soybean accessions and 39 advanced lines available from the National breeding programme were evaluated for soybean rust resistance. These evaluations were conducted at MUARIK and NaCRRI during 2011 and 2012. In addition, the 91 soybean accessions were assessed for phenotypic and genetic diversity. Similarity matrices were calculated for SSR data for 91 soybean accessions and clustered using NTSYSpc (Version 2.2, USA). The genotyping of soybean accessions with 10 standard SSR primers for soybean fingering revealed an average of 5.3 alleles per locus. Thus significant genetic variation and high polymorphism were present among exotic soybean accessions indicating high divergence among evaluated genotypes hence could be used to broaden soybean genetic base. SSR markers revealed high polymorphism and confirmed known morphological trait differences among accessions. However, local soybean varieties had low genetic diversity as revealed by the dendrogram which clustered them into one group. Soybean accessions (P1 615437, P1 567053, P1 628861, PI 635999, PI 628959, Serenade, PI 628812, PI 567104B and PI 567025A0 had yield of more than 3 tons ha-1 which suggested that they had high yield potential. Soybean accessions P1 462312 and P1 459025 with known specific resistance genes Rpp3 and Rpp4 respectively to soybean rust at MUARIK and thus are recommended to be used in improving resistance in already released varieties in Uganda. There is need to evaluate them in other regions of Uganda to assess whether they have broad spectrum resistance. Rust severity was generally higher in late maturing soybean accessions compared to early maturing accessions. There was an increase in rust severity among soybean lines as they matured with the highest severity observed at R6. Soybean accessions P1 417126, P1 416826A and P1 615437 and the breeding lines BSPS 48A-27 and BSPS 9.2B showed an immune reaction to P.pachyrhizi at the two stations making them useful source of resistance to soybean rust. Therefore, there is need for hybridization between the resistant soybean accessions and the local adapted varieties to develop rust resistant varieties.