Appearance of a new race of puccinia striiformis f. sp. tritici in Iran

Yellow (stripe) rust is the most serious disease of wheat in Iran. Total yield losses in epidemic years is estimated up to 15% . Most of released cultivars grown under intensive cultivation are usually damaged after few years. The widespread cultivation over thousands hectares of accepted cultivars such as Falat by farmers, known for their adaptation to abiotic stresses in irrigated wheat areas, was perhaps the major reason for stripe rust outbreaks of 1993 in Iran. Attila 50 (Attila CM 85836-50Y-0M0Y- 3M-0Y), released in Iran as c.v. Chamran, is cultivated more than a quarter million hectares. This cultivar has been release six years ago for warm to moderate temperature zone in Iran. This cultivar appeared to be susceptible in Yemen in 2002. Attila is believed to carry Yr27 and 2 or 3 minor genes, had 0-20 MR responses to yellow rust in the adult plant stage in the different parts of Iran. In 2003 the first symptoms of susceptibility of this cultivar was observed in several fields in Kermanshah and Fars providences indicating the appearance of a new race of the pathogen in those areas. At the moment the population of this race is limited, but its spread in future is not far from anticipation. After increasing spores, the new isolate was inoculated on lines of the standard set of stripe rust to determine the race of the isolate. The results showed that the new race was 166E134A+, which is reporting for the first time from Iran. This race has virulence on Yr2 Yr2+Yr7 Yr7+Yr2, 6+ Yr9 Yr2, 9+ Yr24 YrSD YrA genes. To retard and postpone the epidemics of the new race, it is recommended to reduce the grown areas of Charnran gradually, and limit it to dry and warm areas such as Khuzestan, where there is less chance for the disease to be epidemic.