Identification of new sources of resistance to stem rust race Ug99 (TTKSK) in wheat genotypes

Stem rust disease which caused by Puccinia graminis f. sp. tritici is one of the major wheat production constraints in the high lands of central, south eastern and north western part of Ethiopia. The disease had caused up to 100% yield loss on the unprotected wheat farms. This study was conducted to identify new sources of resistance to stem rust disease. After the removal of genotypes that showed a major gene (race specific) resistance expression at seedling test, 60 selected genotypes were evaluated for their adult plant resistance to stem rust and agronomic traits across three locations (Debrezeit, Adet and Kulmsa) using a 5 × 12 alpha lattice design with three replications. Genotypes showed a highly significant difference (p = 0.001) on the traits of final rust severity (FRS), area under disease progress curve (AUDPC), coefficient of infection (CI) and apparent infection rate (r) at different locations. Moreover, combined analysis of variance also showed the presence of highly significant effects of genotypes, environments and GE interaction on the magnitude of FRS, AUDPC, CI, r, days to maturity (DM), plant height (PH), hectoliter weight (HLW), thousands kernel weigh (TKW) and grain yield (GY) across testing locations. The correlation analysis revealed the presence of positive highly significant (p<0.001) relationship of FRS with both CI (r=0.894) and AUDPC (r=0.877). A positive and highly significant (p<0.001) correlation was also observed between CI and AUDPC (r=0.996) of the tested genotypes. Principal component analysis indicated that only the first four principal components (PCs) explained 86.58% of the total variation among the tested genotypes. Cluster analysis also confirmed the presence of variation among the tested genotypes by dividing them into five major groups. In this study, four bread wheat genotypes (G12, G60, G31 and G52) were found to be resistant to stem rust disease across the three locations and could be used as source of stem rust resistance in future wheat improvement program.