Mating Type In Puccinia Striiformis F.sp.tritici And Sexual Reproduction In Population Diversity Of The Pathogen

Wheat stripe rust,caused by Puccinia striiformis f.sp.tritici(Pst),is a major disease threatening safety of crop food production.Rational selection and depolyment of diseaseresistant varieties can effectively,economically and environmentally prevent and control the occurrence and prevalence of wheat stripe rust.However,the production of new virulence races of Pst often leads to ineffectiveness of resistance in varieties,resulting in a large scale of epidemics of wheat stripe rust.In recent years,studies showed that sexual reproduction is a main way of virulence variation of Pst.The sexual reproduction in Basidiomycetes includes two types: homothallism and heterothallism.And the heterothallism includes the bipolar mating system and the tetrapolar mating system.The mating type(MAT)genes of Basidiomycetes are limited to two types,one is the A mating type locus encoding the homeodomain transcription factor(HD gene),and the other is the B mating type locus encoding the pheromone precursor and pheromone receptor(P/R gene).At present,the MAT genes and the mating system of Pst are not well understood,and the role of sexual reproduction on the genetic diversity of its natural population still needs to be further explored.Objectives of this study were aimed at cloning the HD1 gene of Puccinia striiformis(Ps),identifying the mating system and the alternate host Berberis.spp of Pst,detecting and analyzing the HD1 gene composition of the natural population of Ps in China and the constructed sexual reproduction population of Pst,and analyzing the genetic diversity and structure of Pst population based on the detection results.The results provide an insight into further understanding the mating type of Pst,revealing the role of sexual reproduction on the variation and prevalence of Pst,and a basis for wheat stripe rust control.The main findings were as follows:1.The HD1 genes of Pst have certain diversity and conservativeness.In this study,a total of 11 HD1 gene sequences were cloned from the natural population of Ps,10 of which were from Pst and one from Puccinia striiformis f.sp.hordei(Psh).The analysis of sequence alignment,phylogenetic tree and HD1 gene testing results of natural populations showed that the HD1 genes of Pst have certain diversity and conservativeness.Gene PstHD1-e8 was the main HD1 gene type in the currently prevalent Pst population in China,and gene PshHD1-e1 was the HD1 gene type specific to Psh.2.The mating system of Pst is tetrapolar.The probability of producing aecia after mating between pycnia with the same HD1 gene type was 0%,and the probability of producing aecia after mating between pycnia containing different HD1 gene types was 45.5%,and the confidence level that the probability of producing aecia in the latter was less than 100% was 99.5% based on the 0-1 distribution parameter interval estimation,indicating that the HD1 genes of Pst have biological functions,and that there were also genes that are not linked to the HD genes and perform biological functions during sexual reproduction.3.Sexual hybridization of Pst is the main reason for the diversity of HD1 gene combination types in Pst population.The HD1 gene combination type of progeny produced by sexual hybridization differ from the parents,however the HD1 gene combination type of progeny produced by sexual selfing was same as the parents,without new combination types.4.The Pst populations in Gansu and Shaanxi provinces were abundant in HD1 gene combination types and have high genetic diversity.At least 25 HD1 gene combination types existed in Pst populations in 11 provinces of China,and Gansu and Shaanxi provinces were the most abundant,with at least 14 types present in Gansu province,covering most of the combination types in nine other provinces except Xinjiang and Tibet.The differences in virulence phenotypes among isolates of the same HD1 gene combination type and among isolates of different HD1 gene combination types in this region suggest that complex genetic exchange and variation existed in the natural populations of Pst in this region.5.The Pst populations in Tibet and Xinjiang were two relatively independent populations compared to other regions in China.Population structure analysis and cluster analysis based on the results of HD1 gene testing of Pst isolates collected from 11 provinces in China showed that both the Pst Populations in Tibet and Xinjiang were relatively independent populations with unique population composition and low genetic identity to other regional populations.The HD1 gene combination type of the dominant isolate in the Pst population of Tibet was T1(PstHD1-e2 and PstHD1-e4),and the isolates of this combination type were distributed only in Tibet,and the T4(PstHD1-e3 and PstHD1-e8) isolates dominant in the Xinjiang population were distributed only in Xinjiang.6.The Yunnan-Guizhou plateau is abundant in Berberis,and eight species of Berberis were identified as alternate hosts for Pst.The Berberis plants was found in 43 out of 49 surveyed sites in the Yunnan-Guizhou plateau.Eight species of Berberis were reported for the first time as alternate hosts for Pst,namely B.julianae,B.tsienii,B.veitchii,B.wilsonae,B.wilsonae var.guhtzunica,B.franchetiana,B.lepidifolia and B.pruinose.