Analysis Of Population Genetic Structure And Regional Relationships Of Puccinia Striiformis F.Sp. Tritici In Gansu,Sichuan, Ningxia And Shaanxi Provinces Of China

Wheat stripe rust, caused by basidiomycete fungus Puccinia striiformis f.sp. tritici (Pst), is one of the important cereal diseases worldwide. Since1949, four nationwide epidemics occurred in China consecutively, causing severe yield losses, raising a great threat to wheat production and food safety in China. Therefore, knowledge of epidemic patterns, population dynamics and disease prediction of Pst are necessary to be studied. By continuous monitoring of Pst races and simulation of meteorological data, previous studies basically confirmed the locations of major oversummering areas of Pst and its basic dispersal pathway over regions. However, the detailed dispersal pathway of Pst in these oversummering areas and the major migration direction among different regions are still under investigation. In addition, population structure of Pst changed with the arise of new races while known resistance genes of Chinese wheat differentials are limited. It is hard to understand the population genetic structure of Pst comprehensively using classic method for race identification. DNA polymorphism, as neutral markers, has the ability of analyzing population genetic structure of Pst in molecular level and will play an important role in understanding the dispersal route, guiding for disease resistance breeding and reasonable distribution of resistance genes.This study collected Pst infected leaves from35counties covering areas with wheat stripe rust frequently occurred, including Gansu, Sichuan, Ningxia and Shaanxi provinces between October,2009and June,2011. A total of897isolates were obtained after purification of single spore including396isolates in Gansu Province,258isolates in Sichuan Province,176isolates in Ningxia Province and67isolates in Shaanxi Province. All isolates were amplified by8pairs of amplified fragment length polymorphism (AFLP) markers modified by fluorescence at5’end. The effects of sampling year, sampling season, sampling location and sampling cultivar on population genetic structure of Pst were intensively studied. In order to study the distribution of Pst epidemic races in the four provinces,19Chinese differentials were used to identify161isolates which were randomly selected from all the samples. The correlation between AFLP polymorphism and virulence characteristics was also tested. Additionally,9pairs of SSR markers (codominant marker) were also used to amplify200Pst isolates from the four provinces. The results obtained from SSR markers were compared with those obtained from AFLP markers. Moreover, SSR dataset was also used to calculate historical and contemporary migration rate (M) among regional subpopulations in the four provinces using coalescent method. Likelihood ratio test was used to infer asymmetric dispersal direction between pair-wise populations to draw the dispersal route of Pst among four provinces finally. The conclusions are summarized as follows:1. Gene diversities among regional, seasonal and annual subpopulations of Pst were varied significantly in Gansu Province, but low Φpt values (0.033-0.157) suggested that genetic differentiation was mainly within subpopulations. Shared genotypes among each kind of subpopulations supplied molecular evidence for gene flow among subpopulations. 2. Gene diversities among regional and annual subpopulations of Pst in Sichuan Provinces also varied significantly. Gene flow between subpopulations within Sichuan Province was less frequent than that within Gansu Province. Shared genotypes and low P(Sex) values suggested gene flow between Pst populations from Gansu and Sichuan Basin and the major migration direction was from Gansu fall population to Sichuan Basin population.3. Ningxia and Gansu populations of Pst revealed the similar level of genetic diversity. The40%shared genotypes supplied molecular evidence for gene flow between them. The Liupan Mountain had some effect on limiting gene flow between populations in two sides of the mountain.4. The gene diversity of Shaanxi population was significantly lower than that of Gansu and Sichuan populations, but gene flow among three populations was frequent. In addition, the gene flow between Shaanxi and Gansu populations was higher than that between Shaanxi and Sichuan populations.5. The PTLPT approach revealed the possibility of recombination in subpopulations of Pst in all four provinces. Race identification suggested that Su11and Hybrid46were major race groups in four provincial populations of Pst. The predominant races in each provincial population were slightly different while they were mainly CYR33and Sul1-7. Cluster result of races did not show significant correlation between AFLP loci and virulence characteristics.6. Genetic structure of Pst populations in four provinces estimated using AFLP and SSR were consistent. Historical and contemporary migration rates both suggested the asymmetric migrations which were mostly among regional subpopulations in four provinces. Southern Gansu was estimated as the inouclum center in four provinces and Sichuan Basin accepted inoculums from Southern Gansu as well as Western Sichuan.