Population Genetic Diversity Analysis Of Puccinia Triticina In Hebei Province From2001to2010Based On Virulence And EST-SSR

Wheat leaf rust, caused by Puccinia triticina, is an important epidemic disease in wheat-grown region of worldwide. In P. triticina population, arise of new virulence pathotypes and composition changes of pathogen races were main factors that causing cultivars loss resistance and leading to leaf rust happened seriously. Research about population genetic structure of P. triticina can help understand the genetic variablity of P. triticina, which is very important for rational distribution and utilization of resistant cultivars. In this study, total247isolates of P. triticina collected from Hebei Province of China in2001-2010were analyzed for virulence identification and genetic diversity by EST-SSR primers. The results were as follows:1. Based on infection types that204(there was not virulence data of the rest43isolates) isolates reflected on16fixed host differentials and20auxiliary host differentitals,204isolates included164pathotypes, and THTT, THST, PHRT, THTS, PHTT were predominant pathotypes of204P. triticina isolates. Dendrogram analysis showed that virulence similarity coefficient was0.53-0.98,204isolates were divided into13clusters (V1-V13). Clusters V2-V13included8.33%isolates which were different largely in virulence from isolates that clustered in group V1, and91.67%isolates were clustered in group V1. Most isolates that collected from2001-2006were distributed in clusters V1-1, V1-2-1, V1-3, V1-7, while most isolates that collected from2007-2010were distributed in clusters V1-2-2and V1-2-3, indicating that the virulent structure of P. triticina population had changed largely since2007.2. Two hundred and forty-seven isolates were analyzed by21pairs of EST-SSR primers. Seventeen of21pairs of primers can amplified clear and stable bands from247isolates. While there were no polymorphism bands amplified from primers PtSSR0536, PtSSR3145and PtSSR0801. The rest14pairs of EST-SSR primers could amplified54bands. Dendrogram analysis based on EST-SSR data showed that molecular similarity coefficient was0.67-0.99. All tested isolates were seperated in four branches (S1-S4) at 74%similarity. Branch S1were divided into two subbranches (S1-1, S1-2) at75.8%similarity; Branch S1-2were seperated into6clusters (S1-2-1-S1-2-6) at82.2%similarity. P. triticina isolates collected from2001-2006were clustered in subbranches S1-1and S1-2-1, however, isolates collected from2007-2010were clustered in subbranches S1-2-2-S1-2-6and branches S2-S4, indicating that the genetic structure of P. triticina population had changed largely since year2007.3. The Nei’s gene diversity (H) revealed by virulence and EST-SSR molecular marker revealed was0.30and0.27respectively, indicating that the virulent diversity was higher than genetic diversity that revealed by EST-SSR. Correlation analysis showed that the correlation coefficient between the virulence polymorphism and molecular polymorphism was0.006, showing that there did not exist correlation between the virulence and molecular polymorphism. Principal coordinates analysis also showed that there was no correlation between the molecular polymorphism and virulence polymorphism.4. Forty-nine isolates belonging to five predominant virulent pathotypes (THTT, THST, THTS, PHRT, PHTT) were analyzed for virulence polymorphism and molecular polymorphism. The similarity coefficient of virulence and molecular was0.82-0.98and0.67-0.99respectively, indicating high diversity of both virulence and molecular polymorphisms. Dendrogram analysis showed that the same pathotype may had different virulence and different DNA fingerprints and gathered in different clusters, and different pathotypes may had similar DNA fingerprints and gather in same cluster. There was correlation between pathotypes and virulence polymorphism (r=0.574), while no correlation existed between pathotypes and EST-SSR molecular polymorphism (r=0.025).5. Based on EST-SSR data set, population genetics parameters showed that the populations of P. triticina maintained high genetic diversity, while there existed differences in genetic diversity among populations, the genetic diversity ranked from low to high:2010,2003,2008,2002,2006,2005,2001,2004,2007,2009populations. The ranges of genetic distance (D) was0.0070-0.1914. Phylogenetic analysis showed that10tested populations were divided into three groups. Populations2001-2006were in group Ⅰ,2007and2008populations were in groupⅡ,2009and2010populations were in groupⅢ, and populations that belonging to same group had close genetic relationship. Populations2001-2006had closer genetic relationship with populations2007-2008than with populations2009-2010, indicating that the longer time, the larger differences between populations. In Hebei Province, the genetic structure of P. triticina population changed largely in2007, and after two years in2009changed largely again, while during2001-2006there was no chang nearly, indicating that the varying frequency of population genetic structure tends to rise.6. Genetic differentiation analysis with the10populations based on EST-SSR data set, indicated that there existed genetic differentiation both intra-population and inter-populations, and genetic variation from intra-population contributed72.54%to total variation showing that genetic variation mainly origined from intra-population. The gene flow(Nm) among the10populations was1.38>1, showing that there was gene flow between the ten populations. The gene flow of2001-2006populations were stronger (the ranges of Nm were4.64-13.59) than populations2007-2010(the ranges of Nm were1.00-3.75), indicating that there was low genetic differentiation in2001-2006populations, while there occurred high genetic differentiation in P. triticina population since2007and the genetic structure of P. triticina population changed largely, indicating that gene flow was one of important factor that P.triticina population maintain similarity.