Efficiency of resistance genes in wheat to powdery mildew in some centers of disease incidence in Iran

Wheat powdery mildew caused by fungal pathogen Blumeria graminis f.sp. tritici is a destructive wheat disease, occurring in regions with cool and humid climates. In order to investigate the changes in pathogenicity of the disease and to identify the effective genetic source of resistance, a total of 29 wheat genotypes with different resistance major genes (Pm) were studied in two hotspots of Gorgan and Sari under natural incidence of the disease over 2015-2018. Resistance reaction of the genotypes was evaluated by disease development, disease severity and coefficient of infection. The results indicated that mean of coefficient of infection for Gorgan was larger than that for Sari in all three years of the study. The reaction of some genotypes showed apparent differences between the two regions during the years of study. The highest genetic distance was observed between Ralle (Pm3d) and Holger (Pm6). NK-747 (Pm6) and Maris Huntsman (Pm2+Pm6) as well as Amigo (Pm17) and Maris Huntsman (Pm2+Pm6) showed the highest genetic similarities to each other. A total of 65.78% of the data variation was justified by principal component analysis on the basis of the coefficient of infection. The genotypes Maris Dove (Mld+Pm2), Shamrock (with unknown Pm), Broom (Pm3d) and Axona (Pm2+Pm3d+Mld) expressed effective resistance over the years and locations. The total results of this research indicated variations in the virulence of wheat powdery mildew population during the years of the experiment. This finding emphasizes on the necessity of constant monitoring of the disease in the infected areas. The genes with effective resistance identified in this study could be used in resistance breeding to powdery mildew especially for Gorgan and Sari.