| Wheat stripe rust, caused by Puccinia striiformis f.sp. tritici, is the most important disease in wheat production in China. Growing rust-resistant cultivars is the most economical and effective measure. However, the resistance usually was breakdown in wheat cultivars, and continuous occurrence of new virulent races was the main cause. Virulence variation caused occurrence of new virulent races. It had been proved that the approaches to virulence variation were mutation, heterokaryosis, and so on, in which gene mutation was the exclusive approach to producing new virulence genes. The biological effects on the stripe rust fungus induced by UV, had been reported; but the reports about variation on level of molecule in Puccinia striiformis f.sp. tritici were not found. RAPD analyses may detect the polymorphisms in genomic DNA. Most single nucleotide changes in a primer sequence caused a complete change in the pattern of amplified DNA segment. The stripe rust urediospores were treated by UV to obtain the mutant cultures in pathogenicity, and the cultures were analyzed with RAPD technique in order to lay the foundation for studying the mechanism of the virulent gene variation. The probability of forecasting the rust resistance stability of the wheat cultivars was verified by seeding inoculation tests.1. Urediospores of the Shuiyuan 11 pathogenic type1-4, CY29-3 and CY23-2 were treat by UV. The proper time treated was12 minutes, 8 minutes and 5 minutes respectively, when the urediospores lethality rate reached to 90% or so. Mutants in pathogenicity were not obtained after urediospores of Su-1-4 were treated for 12 minutes through six bathes of selection. Urediospores of CY29-3 were treated for 8 minutes, and three mutant cultures in pathogenicity were obtained including Hybrid 46 isolate, Jubilejina2 isolate and Funo isolate. Two isolates were obtain after stabilization for 4 generations, including Jubilejina2 isolate and Funo isolate. Reaction type of Jubilejina2 isolate was type 4 on Jubilejina2, but that of the original race was type 0; and reaction type of Funo isolate was 2, while that of the original race was 4. Urediospores of CY23-2 were treated for 5 minutes, and two mutant cultures in pathogenicity were obtained, namely Jubilejina2-23 isolate and Shuiyuan 11 isolate, in which Jubilejina2-23 isolate kept its virulence still after stabilization for 4 generations.The pathogenicity of three mutant cultures on the differentials has changed greatly. 2. RAPD analyses were conducted between the original race and the mutant cultures. DNA polymorphisms of Jubilejina2 isolate and Funo isolate were quite distinct from CY29-3. Their polymorphic rates were 10.58% and 11.57%. DNA polymorphisms of Jubilejina2-23 isolate were also quite distinct from CY23-2. So UV irradiation could cause great variation of the genome DNA of the wheat stripe rust of fungus and the mutation loci were complicated. 3. Wheat stripe rust races CY29, 31, 32, two mutant cultures of CY29-3 and the mutant culture of CY23-2 were used to identify the seeding resistance on the different cultivars grown in Huanghe and Huaihe river wheat area. The results testified that the resistance stability of the wheat varieties could been forecasted by inoculation of the mutant cultures. The results identifying the adult plant resistance with the mixed races (CY29,CY31,CY32,Su-14) indicated that 10 varieties were resistant to mixed races, while only one cultivars, Zhoumai 17, was resistant to three wild cultures. Most of them could be the slow rust type or high temperature resistance to strip rust on adult plant.
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