| Wheat powdery mildew, which is one of the most severe wheat disease worldwide, cause tremendous decrease on wheat productivity. The most effective and efficient way to control the disease is to apply disease resistance cultivars. However, due to redundancy of the pathogen races and the high rate of gene recombination, virulence of pathogen varies very fast. In addition, the widely application of single resistant cultivar can also accelerate the production of new virulent genes and dominant races and finally lead to resistance lose of the varieties. In order to understand the population structure of powdery mildew and the theory of variation, study the changes of virulent genes, and to provide theoretical proof for wheat disease resistance breeding and chemical control, the following experiments were conducted:Samples of wheat powdery mildew were collected from four cities of Shaanxi Province. including Baoji. Xi’an. Xianyang and Weinan, during the starting and increasing periods of the disease(normally from April to middle of May) in 2013 and 2014. The samples were isolated and then purified. Finally a total of 125 and 113 single strains were identified using 32 different varieties. It was found that the structure of virulence genes was complex and the change was fast. There was significant difference between different regions in the same year and also different years in the same regions in terms of virulence gene structure. Besides, it also showed that virulence genes of the disease in Shaanxi Province have strong united pathogenic influences. The frequency of 11 virulence genes combination was highest, which were 16.00% and 20.35% in two years. And a number of virulence genes, including V1、V3b、V3c、V3e、V3f、V7、V8、V19、V1+2+19, have reached virulent frequency of 69.17% or even higher, which means there genes were prevalent in Shaanxi and the relevant resistance genes should not be valuable any more. While some other virulence genes, including V2、V3d、V4a、V4b、V5(Mli)、V13、V18(1c)、V21、V24、V30、V2+6、V2+Mld、V2+6+?、V4b+Mli、V4+2+?、V5+6, had virulent frequency lower than 17.23%, suggesting that genes resistant to these virulence genes are still quite valuable in wheat breeding.POPGENE32 and NTsys-2.10 e were used to conduct diversity analysis of the virulence gene of powdery mildew in 2013 and 2014. It showed that there were significant differences between different years as well as different regions in terms of the virulence gene diversity. Genetic diversity index were between 0.0968~0.2008 and 0.1789~0.2459 while Shannon’s diversity index were between 0.1612~0.3193 and 0.2306~0.3828, which indicated that there were rich diversity within the population structure of the pathogen. Genetic differentiation coefficient and gene flow analysis showed that the main source of variation is genetic variation within the population. In the meantime, there were wide gene interchange among different regions. According to genetic identity analysis and population cluster analysis, there was no significant correlation between genetic distance of virulence and geographic distance.AFLP was applied to study the population genetic structure of powdery mildew in Shaanxi and Gansu. It showed that there was significant difference among different regions in terms of genetic diversity index(H), which is between 0.0847 and 0.1384. And percentage of polymorphic site(P), between 46.00% and 67.24%, also indicates that the genetic diversity of population were relatively high. Genetic distances among the five populations distribute between 0.0010~0.0244 while genetic identity between 0.9759~0.9990, which suggested that the genetic distance of the five populations are close and there is a high possibility genetic identity. UPGMA analysis showed that the five populations were classified in two clusters, one group included Tianshui, Gansu and the other group included Baoji, Xi’an, Xianyang and Weinan, which make sense in terms of real geographic distance. It manifests that there is a positive correlation between genetic distance and geographic distance to some extent. Based on the cluster analysis of genetic distance of virulence among populations, Xianyang and Weinan were clustered together while Xi’an and Baoji were clustered together. However, according to cluster analysis of genetic distance of DNA among populations. Xianyang and Weinan were clustered together and then clustered with Xi’an. Hence, there is no correlation between diversity based on virulence and DNA.A total of 60 strains were selected randomly from 113 samples in 2014 to carry out the resistance experiments to triadmefon. It showed that the average EC50 and resistance level of powdery mildew in Shaanxi were 152.54mg/L and 73.39 fold. The highest EC50 and resistance level were 799.78mg/L and 201.78 fold, respectively. And 93.33% of the strains showed resistance to triadmefon and 58.33% of the strains showed high level of resistance. To conclude, the sensibility of Bgt to triadmefon was decrease in Shaanxi Province. |
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