reaction of rainfed wheat advanced lines and cultivars at their seedling stages to two races of puccinia striiformis f. sp. tritici

to evaluate the reaction of some wheat advanced lines and cultivars to yellow rust at seedling stage, seeds of 200 accessions were planted in 5cm diameter pots (4-6 seeds per pot) in greenhouse. the seedlings were inoculated with fresh harvested urediniospores of two different races of puccinia striiformis f.sp. tritici (134e134a+ from karaj and 134e142a+ from maragheh, iran) when the first seedling leaves were fully expanded. inoculated plants were placed inside a small plastic covered cage and kept at 10°c and 90% rh in the darkness for 48 hrs, and then transferred into a greenhouse of standard conditions (16 hours of light at 15°c and 8 hours of darkness at 10°c). the reaction of each line/cultivar was evaluated using mcneal et al., (1971) scale 15–17 days after inoculation. the results showed that 49% of wheat lines/cultivars were susceptible (infection types 7–9), 39% completely resistant (infection types 0-2), and 7% incompletely resistant (infection types 3–6) to race 134e134a+. moreover 55%, 30%, and 9% of the accessions were respectively susceptible, completely resistant, and incompletely resistant to race 134e142a+. in addition, 41.5%, 24.5%, and 1% of the accessions were susceptible, completely resistant, and incompletely resistant to either one of the races respectively. high frequency of genotypes with susceptibility (7-9 reactions) indicates that most entries are in possession of no seedling resistance genes or have genes that yellow rust pathotypes are virulent to (yr2, yr6, yr7, yr9, yra and yrnd). resistance reaction type genotypes are in possession of at least one seedling resistance gene to which yellow rust pathotypes are not virulent. according to the results, cultivation of lines/cultivars with resistance responses can be recommended for the areas where these races or similar ones are prevailing. moreover some accessions with susceptibility reaction at their seedling stage may possess the ability to develop resistance at their later higher field developmental stages.