Association Analysis On Puccinia Striiformis F.sp.tritici Of Sexual And Asexual Populations

Wheat stripe rust(yellow rust),caused by Puccinia striiformis f.sp.tritici(Pst),has been a severe threat to almost all wheat production regions worldwide.The pathogen mainly spreads by wind-borne.Epidemics of the disease can lead to a remarkable yield loss,even no harvest.The complete life cycle of Pst has not been determined until identification of Berberis as alternate host of the pathogen.Genetic variation,resulted from mutation,heterokaryosis and sexual reproduction,giving rise to new races.The new races often overcome the resistance of wheat cultivars within 3～5 years.So far,studies showed that sexual reproduction is a main approach for virulence variation of Pst.Therefore,many researchers conducted a series of studies on sexual propagation of the pathogen.This study was aimed at collecting Pst samples from wheat fields and naturally rusted barberry in Huzhu,Qinghai in 2018 to compare the relationship of both Pst populations by phenotyping and genotyping for confirming the role of barberry in occurrence of wheat stripe rust in this region.The results provided a basis for management of wheat stripe rust in this region.The main results were as follows.1.Isolates from sexual population had a smaller virulence spectrum compared to those from asexual population.While sexual population had a higher virulence diversity and ratio of new strains.Isolates from barberry had a higher virulence frequency on Yr8,Yr10,Yr32,Yr26,Yr27,Yr Exp2,Yr2 in comparison to those from wheat,which shows 9 times higher virulence frequency on Yr8.However,the virulence frequency on YrTr1,Yr43,Yr3,YrSp,YrTye,Yr6,Yr7,Yr17,Yr28,Yr9,Yr18,Yr1,Yr29.Yr25 and Yr44 was lower of isolates from barberry.The Nei’s diversity was 0.403 and Kosman index was 0.652 of isolates from barberry,and both indexes of isolates from vicinal wheat were 0.285 and 0.412 respectively.The ratio of new Pst strains of sexual population was 72.7% and it was 36.3% of asexual population..2.Sexual population and asexual population shared some same or similar virulence patterns.Isolate B15 from barberry had a same virulence pattern on 24 NILs with isolate W11 from wheat.Similar coefficient based on the virulence on 24 resistant genes showed that with similar coefficient of 0.953,isolate B10 from barberry gathered into a clad with isolate W21,so were isolate B15 and isolates W9,W12 from wheat.PCo A revealed that isolates from barberry and those from wheat were clustered together.Isolates B26 and isolate W10 also shared a new same virulence pattern on 19 China differential hosts.3.Sexual population not only shared a same genetic composition with asexual population,but also had a richer allele diversity and genetic diversity in comparison to asexual population.In all locus,there were some same alleles in both populations.But in loci SUNIPst15-30,loci RJ27,loci SUNIPst10-48,loci SUNIPst11-44,loci CPS34,loci PstP031,loci CPS32 and loci RJ3N,some unique alleles were only detected in sexual population.Shannon’s information index and expected heterozygosity of sexual population were 0.701 and 0.368.Both indexes of asexual population were 0.601 and 0.326 respectively.4.Barberry can provide inoculum for the occurrence of yellow rust,which can affect the structure of the Pst population.Nm value between sexual population and asexual population was greater than 1.Structure result based on Bayesian information criteria showed that when K=2,sexual population and asexual population shared similar genetic background.According to DAPC,Pst from sexual population and those from asexual population obviously gathered together.The results above revealed that the genetic structure had some similarity between both populations.