Virulence analysis and effectiveness of new sources of resistance to barley powdery mildew (Blumeria graminis f. sp. hordei) in southwestern regions of Iran

Barley powdery mildew caused by the biotrophic obligate pathogen, Blumeria graminis f. sp. hordei, is one of the most important foliar diseases in major barley production areas in Iran. To determine the virulence spectrum of the powdery mildew pathogen in southwestern regions of the country and effectiveness of new sources of resistance, barley powdery mildew trap nurseries were established and evaluated under natural field conditions for disease development in three disease prone locations including Zarghan, Ahvaz, and Dezful during 2013-14 to 2017-18 cropping seasons. The trap nurseries consisted of a differential set including the barley cultivar Pallas and 18 near-isogenic ‘Pallas’ lines and a supplementary set including 34 barley cultivars carrying known or unknown resistance gene(s). Our results showed that there is virulence variation in the population of the pathogen in different locations. While the resistance genes Mla6, Mla14, Mla7, Ml(No3), Mla12, Ml(Em2), Mla13 and Ml(Ru3) were effective across the years and locations, the Mlk, Mlh, MlLa and Mlp genes were ineffective in most years and locations. New virulence factors matching Mla6, Mlp, Mlg+MlCP, Mla7 and Mla3 genes were detected. Ineffectiveness of all resistance genes except the recessive mlo allele in Dezful and Zarghan over years indicating that the pathogen population in Dezful and Zarghan are more aggressive than Ahvaz. We concluded that the European mlo carrying barley cultivars and other sources of resistance with a combination of genes, such as Meltan and Escort could be considered as effective sources of powdery mildew resistance to be incorporated in the national barley breeding programs for the southwestern regions of Iran.