Stem rust appraisal of local and global wheat germplasm with a new virulence threat to resistance genes

To ensure adequate diversity of genetic resistance to Puccinia graminis f. sp. tritici ( Pgt ) destructive stem rust disease, the potential threat posed by Ug-99 race group or other new virulence should be taken into account. A total of 117 wheat germplasm including 64 ICARDA genotypes carrying stem rust ( Sr ) resistance genes and 53 Egyptian cultivars were appraised against stem rust during 2020–2022 at two locations (Sakha and Sids Research stations). Stem rust susceptibility at both locations during the year 2021 was higher than other years, since they reached 90S for cultivars at Sids and 100S for Sr genes at Sakha. Eleven Egyptian cultivars, Sakha-93, Sakha-94, Gemmeiz-3, Gemmeiza-12, Giza-144, Giza-155, Giza-156, Giza-170, Sids-8, Sids-11, Sids-13 and three resistance genes Sr31 , SrSatu and SrNin , exhibited specific resistance (0-MR) at both locations over three years. However, the most susceptible cultivars were Misr-1 and Misr-2, since they reached maximum severity 80S and 90S, respectively. The most effective all stage resistance genes were Sr31 (100%), followed by Sr24 and Sr38 (92.30%). A strong and perfect negative correlation were recorded between average coefficient of infection (ACI) and relative resistance index (RRI) appraised on Egyptian cultivars and resistance genes at adult plant stage. Gene postulation and molecular markers both indicated to the presence of effective genes Sr31 and Sr24 in resistant wheat cultivars mentioned above, while ineffective gene Sr25 was detected in both highly susceptible cultivars Misr-1 and Misr-2. Although genes Sr31 and Sr24 both confer effective resistance against local Pgt races. However, additional broad-spectrum resistance genes should be incorporated in breeding program.