Identification of the virulence factors of Blumeria graminis f.sp hordei, the causal agent of barley powdery mildew in northeast and northern regions of Iran

Powdery mildew of barley caused by the fungal pathogen, Blumeria graminis f.sp. hordei, is one of the most important leaf diseases of barley in Iran. This study was carried out to determine the virulence factors in the population of the fungus causing powdery mildew in major conductive regions of the disease in the northeast and north regions of Iran and to identify new sources of resistance. Trap nurseries (53 lines and cultivars) including cv. Pallas, 18 near-isogenic lines in the background of Pallas and a supplementary set including 34 cultivars carrying known or unknown resistance gene (s) were evaluated against powdery mildew under the natural conditions at four powdery mildew hotspot locations in northeast and north of Iran including Mashhad, Karaj, Gorgan and Ghaemshar, during three consecutive cropping seasons (2014-2016). The results of evaluation of near-isogenic lines and supplementary set in different regions showed that there was a variation in virulence spectrum of the pathogen in these locations. Virulence factors for Mlk(1), Mlp, Mlat, MlLa, Mlh, Mla22 and Mlk resistance genes appear to be common in all locations. These genes are reported as ineffective resistance genes in Iran. Virulence for the Mlp gene that was reported to be effective in many regions was appeared in Mashhad, Gorgan and Ghaemshar. The results of this study also indicated that the new virulence factors is appeared for the MlLa gene in Mashhad, Gorgan and Ghaemshar, for the Mlg and MlCP resistance genes in Mashhad and Gorgan and for the Mla3 resistance gene in Mashhad. The findings of this study indicate that the Mla7, Ml(No3), mlo5  Mla9, Mla13, ، Ml(Ru3), Mla10, Ml(Du2), Mla12, Ml(Em2) are effective in Iran and could be used as new sources of resistance in breeding programs.