Barley yellow (stripe) rust, caused by Puccinia striiformis West. f. sp. hordei, has increased recently in some parts of Iran (Safavi et al., 2013). In order to study and identify the barley yellow rust races, thirty-six yellow rust samples were collected during 2012-2013 from barley, wild barley (Hordeum morinum) and wheat in different provinces of Iran. The yellow rust samples were used to inoculate Afzal (barley cultivar) and Morocco (wheat cultivar), susceptible to all Puccinia striiformis f. sp. hordei (Psh) and Puccinia striiformis f. sp. tritici (Pst) isolates, respectively. Then we focused entirely on Psh isolates. Virulence factors and races of barley yellow rust were determined based on avirulence/virulence formula on barley differential seedlings (Chen et al., 1995). In all, ten races were identified in this study: PSH-51, PSH-56, PSH-74, PSH-83 (having virulence on differentials 1, 5, 7, 10, 12) , PSH-84 (virulent on 1, 5, 6, 7, 10, 11), PSH-85 (virulent on 1, 4, 11), PSH-86 (virulent on 1, 2, 4, 11), PSH-87 (virulent on 1, 5, 7, 9, 10, 12), PSH-88 (virulent on 1, 5, 8, 12) and PSH-89 (virulent on 1, 5, 10, 12). All the ten races were new for Iran and the study of barley yellow rust races was the first in Iran. Seven races (PSH-83, PSH-84, PSH-85, PSH-86, PSH-87, PSH-88 and PSH-89) have not been reported anywhere before (Holz et al., 2013; Wan and Chen, 2012). The races PSH-87 and PSH-84 with six virulence factors each had the widest virulence spectrum; PSH-51 and PSH-85 were most narrow with three virulence factors each. None of the races had virulence on cultivar Emir having resistance genes rpsEm1, rpsEm2 and only one race had virulence on each of resistance genes Rps4 (Yr4), rpsHF, rpsVa1, rpsVa2, Rps1.c. The highest virulence frequency was determined for genes rpsHi1, rpsHi2 (83%) and rps2 (67%).
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