Virulence of Puccinia striiformis f. sp. tritici in Khuzestan Province of Iran

Yellow rust caused by Puccinia striiformis f. sp. tritici is undoubtedly, the most important fungal disease of wheat especially in Central and Western Asia causes significant annual yield losses. To investigate the population structure of the pathogen, isolates were collected from four regions and tested on 26 differential genotypes with known resistance genes in greenhouse and field conditions on the territory of Khuzestan province in Iran during 2009 - 2010. According to the results of race determination, races 4E14, 4E15, 6E128, 6E148, 6E142, 6E130, 6E158, 134E4 and 166E232 were common in all locations during the course of this study. Isolates with virulence on lines with yellow rust resistance gene Yr2, Yr6, Yr7, Yr7+, Yr6+, Yr9, Yr17, Yr18, Yr25 and YrA represented the most frequent phenotypes. Virulence to Yr1, Yr3V, Yr4, Yr5, Yr10 and YrSU was not found in any of the tested isolates. At the adult plant stage, virulence on wheat genotypes Heines Kolben, Kalyansona, Lee, Avocet R, Federation* 4/Kavkaz, TP1295 and Nord desprez was common during the period of investigation. The frequency of virulence factors in the yellow rust population on the differential genotypes were above 91% for the resistance genes Yr2,Yr6, Yr7, Yr2, Yr6+, Yr18, YrA, Yr2, Yr17, Yr25 and YrA however, virulence frequencies for Yr7+ and Yr8 were less than 10%. Frequency of virulence factors was low for Yr 2+, Yr7+, Yr8, Yr3N and YrSd.