prevalent pathotypes of puccinia striiformis f.sp. tritici in iran

the stripe (yellow) rust in wheat is one of the most important plant diseases in iran. since 1993 several epidemics have occurred in iran causing the breakdown of widely util-ized sources of resistance in wheat cultivars. twenty-seven pathotypes were identified during 2003 and 2004 in greenhouse tests. pathotypes 6e6a+, 6e22a+, 6e130a+, 6e134a+, 6e142a+, 6e158a+, 134e130a+ and 134e142a+ were more common during the course of this study. virulence on plant/s with gene/s yr2, yr6, yr7, yr8, yr9, yr24, yr25, yrsd, yrsp, yr3n, yr2+, yr6+, yr9+, yr7+, yr32+ and yra was detected under greenhouse conditions. the majority of isolates with a high frequency (more than 88%) showed virulence on plant/s with yr2, yr6, yr7, yr9, yra and yr24 genes. no virulence was detected on plant/s with yr1, yr3v, yr4, yr5, yr10 and yrsu genes. in a greenhouse test, frequency of virulence to wheat genotypes with the yr32+, yrsp and yrsd gene was less than 7%; frequency of virulence to all other wheat genotypes was between 19 and 100%. during three years of field study, virulence on wheat genotypes heines kolben (with genes yr2 and yr6), kalyansona (yr2), lee (yr7), avocet r (yra), federation*4/kavkaz (yr9) and tp1295 (yr25) was common. no virulence was observed on plants with yr1, yr3v, yr3n, yr4, yr5, yr8, yr10, yr18, yr24, yr32+, yrsp, yrsd and yrsu genes in the trap nurseries. the coefficient of infection (c. i.) of the adult plant resistance gene, yr18, was between 16-64 with moderate susceptibility and is going to be used in the breeding program in combination with other resistant sources.