Bread Wheat (Triticum aestivum L.) “R” genes Efficacy to Zymoseptoria tiritici Blotch in Central highlands of Ethiopia

Wheat production in Ethiopia has recently expanded in both areas and the use of irrigation-based cultivation methods. However, diseases such as rust and Septoria leaf blotch have emerged as significant pathogens in key agricultural regions, leading to recurring epidemics. Understanding the physiological specialization of these pathogens and identifying potential sources of resistance are essential for developing effective management strategies. This study aimed to assess the efficacy of the bread wheat “R” gene resistance to Zymoseptoria tritici (Z. tritici) and to evaluate the virulence patterns of thirty-two Z. tritici isolates derived from Ethiopian bread wheat. The analysis of disease severity revealed a highly significant main effect attributable to the isolates and the differential lines, as well as notable interaction effects. Median polish analysis indicated specific interactions between the pathogen and the differential lines. Among the isolates, STBI21 exhibited the highest mean disease severity at 64%, while STBI9 was the least aggressive, showing only 9%. Furthermore, STBI20 was identified as the most virulent isolate, with no wheat differential genotypes demonstrating resistance, whereas STBI15 was the least virulent, with 16 out of 25 wheat differential genotypes (64%) showing resistance. The tested Z. tritici isolates displayed significantly varied virulence patterns, affecting between 0% and 85% of the wheat genotypes. Pathogenicity assays revealed 300 isolate-specific resistances among a total of 800 tested. Among the known Stb “R”genes, Stb6, Stb7, Stb10, and Stb12 in cultivar “Kavkaz-K4500” did not provide resistance to any of the isolates. In contrast, Stb8 in cultivar “M6 synthetic”, Stb5 in cultivar “CS synthetic”, and Stb16 in cultivar “Murga and KM7” conferred broad-spectrum resistance to 87.5% of the isolates, representing promising sources of resistance to Z. tritici in Ethiopia. Cultivar “Esrael-493” exhibited the highest number of specific resistances, totalling 14, while the M6 synthetic, CS synthetic, Murga, and KM7 showed the least specific resistance. This information is invaluable for wheat breeders and the agricultural community, aiding them in making informed decisions to manage Z. tritici disease in Ethiopia.