Virulence And Molecular Diversity Analysis Of Puccinia Striiformis F. Sp. Tritici Population In Xinjiang In Relation To Other Epidemic Regions Of Western China

Wheat stripe rust, one of the most destructive diseases, caused heavy losses on wheat production in China in epidemic years. The pathogen, Puccinia striiformis f. sp. tritici(Pst), is an obligate biotrophic parasite with high virulence variability, and the virulence variability is the major reason for disease outbreak again. So it is important to control the disease effectively by knowing the virulence structure and epidemic rules of Puccinia striiformis f. sp. tritici. Xinjiang located in northwest of China, because of the complexity of geographical environment and crop planting system, the disease also a threat to wheat in this area. However, the genetic diversity of Pst population in this region and the relationship between Xinjiang and other regions are absent at present. Based on these reasons, genetic structure of 308 Pst isolates from five provinces(Xinjiang, Tibet, Gansu, Qinghai and Ningxia) and comparison of these regions were analyzed by virulence characteristic and SSR markers. The results of this study will provide basic guidance to control disease.1. 308 isolates were distinguished in 56 races(pathotypes) including 39 previously reported and 17 unknown races based on 19 Chinese differentials. 178 isolates from Xinjiang(R1) identified 27 known races and 8 new races. Of which, the HY46-8 were the dominant races and the ratio was 33.71%, the other races frequency were less than 10%. The CYR32 and CYR33 in Gansu, Qinghai and Ningxia provinces(R2), which were identified 18 races previously known and 6 new races, were the dominant races, the virulence ratios were 26.8% and 18.54%, respectively. In Tibet(R3), the ratio of CYR25 was high than 18.18% in 14 known and 3 unknown races, but others ratio was below 5%. The old races that had narrow host spectrum(prior to CYR28) were only found in Xinjiang and Tibet. The new races that virulent to Yr26 resistance gene were captured in inland regions covering Gansu, Qinghai and Ningxia provinces, but absent in Xinjiang and Tibet autonomous regions indicating the virulence structure were different in geographical positions. Analysis on virulence frequency on Chinese differentials showed that there exist significant difference(P < 0.01) among different populations and the correlation was low in different regions(the correlation coefficient r = 0.0072).2. The virulence diversity parameters revealed the difference in different regions. In total, the number of observed alleles(Na)was 2.0, the percent of polymorphic loci(P) was 98.47% and the effective number of alleles(Ne) was 1.89. The Shannon’s information index(I) and virulence diversity index(H) in three epidemic regions were 0.63, 0.63, 0.60 and 0.23, 0.31, 0.17, respectively, indicating that population virulence diversity in different regions have significant differences(α = 0.05). The virulence diversity of Pst population from inland were higher than Xinjiang and Tibet, which can be caused by the climatic conditions and distribution of host in these areas.3. Analysis the molecular diversity of wheat stripe rust in three endemic regions(Xinjiang, inland and Tibet) using the 15 pairs SSR primers. The Shannon’s indexes of three regions were 0.67, 0.64 and 0.62, respectively. The significant analysis shows that the genetic diversity of Xinjiang population was higher than inland and Tibet. High similarity of genetic was tested in sub-populations of Xinjiang indicated there is no genetic difference among ten sub-populations. For three populations, the differentiation values were 0.04, 0.05 and 0.03, respectively, revealed far genetic distance and significant difference(P<0.01) existed among three populations. Of which, 98% of genetic variation presented within populations and 2% presented among populations. Linkage disequilibrium test based molecular data reveals that sexual recombination maybe exist in Gansu province and absent in Xinjiang and Tibet autonomous regions(rd = 0.07,P = 0.01).4. The genetic diversity of Xinjiang Pst was related to, but had a higher diversity than the other two populations based on virulence and molecular data. The phylogenetic tree constructed and cluster analysis indicating Xinjiang is an independent stripe rust epidemiological regions in west of China. There little gene flow existed between Xinjiang and inland and Tibet regions.