Investigation of wheat genotypes' resistance to stem rust through GGE biplot analysis

Stem rust, or black rust, caused by the fungus Puccinia graminis f. sp. tritici, poses a severe threat to global food security, potentially devastating wheat crops on farms. The damage of this disease in the epidemic condition is 100% of the wheat crops. Frequent epidemics of stem rust have been reported in different regions of the world in the past years. The most effective method to control this disease is identifying and incorporating effective resistance genes from resistant cultivars into desirable wheat genotypes, for establishing durable genetic resistance.

To identify new sources of resistance, an experiment was conducted to investigate the resistance reactions of 30 wheat genotypes and a susceptible check (Morocco) against six Pgt races with distinct pathogenicity patterns (TKTTF, TTTF, TTRTF, PKRTF, PKSTF, and TKSTC). The experiment employed a randomized complete block design with three replications. Each race of Pgt was used separately to evaluate the genotypes.

Phenotyping and analysis of variance (ANOVA) revealed significant phenotypic diversity among wheat genotypes for the measured resistance components (infection type and latent period). Cluster analysis classified the wheat genotypes into three main groups: resistant, susceptible, and moderately resistant to moderately susceptible. Among the wheat genotypes studied, 11 genotypes (35%) exhibited susceptibility to all races, while four genotypes (G1, G2, G3, and G17) (13%) demonstrated resistance to all races. The remaining 16 genotypes (52%) showed moderately resistant to moderately susceptible (specific reaction) responses. The biplot analysis (GGE biplot) identified genotype G17 as the most resistant genotype with a uniform response to all races.

Genotypes with varying degrees of resistance to Pgt races identified in this study can serve as new and sustainable sources of resistance for breeding wheat cultivars with a broad genetic basis of resistance. The use of more races and differential isogenic lines can make it possible to provide more specific conditions to identify the effective resistance genes in each genotype more accurately. Evaluating the resistance of the examined genotypes at the adult plant stage can also lead to the identification of resistance genes at the adult plant stage which are more important than the seedling stage resistance genes. The existence of resistance genes at adult plant stage is not far from expected even if the genotype is sensitive in the seedling stage. It is hoped that the correct, and planned use of effective resistance genes at the seedling stage and adult plant stage together will lead to the creation of new stable resistant varieties.