Virulence Variation Of The Two Puccinia Striiformis Isolates Virulent To Wheat And Barley Based On Sexual Selfing

Stripe rust caused by Puccinia striiformis is an important disease on wheat and barley,seriously influencing production of the two crops.The disease damages barley and wheat through re-infections of urediniospores.Presently,application of disease-resistant varieties is major approaches for management of the disease.However the loss of the resistance of disease-resistant varieties often leads to the outbreak and prevalence of stripe rust.The pathogen of stripe rust has a wide range of hosts including wheat,barley and many gramineous grasses.Wheat form of P.striiformis f.sp.tritici not only mainly infects wheat,and but also a few races of the form infect barley.Compared to mutation and heterokaryosis,sexual genetic recombination represents a high level of virulence variation and is the most means for virulence variation.However,little is known about virulence variation and sexual reproduction of the isolate of P.striiformis virulent both wheat and barley.Therefore,in this study,the two isolates BSR-4 and BSR-5,virulent to both barley cultivar Guoluo and wheat cultivar Mingxian 169 were conductive for selfing on barberry to establish a population of progeny after fertilization.The progeny was tested virulence and avirulence patterns on Yr isogenic lines and differential host for the barley stripe rust.The virulence and avirulence of the progeny were compared to the parental isolates to determine virulence variation,revealing that sexual reproduction of the two isolates in relation to virulence variation.The main results were as follows:A total of 97 selfed progeny were derived from the of the two parent isolates.Compared with the parental isolate,the virulence and avirulence patterns based on near iso-genetic lines,the progeny varied obviously,showing a difference of phenotype at one or two Yr loci.A total of 67 selfed progenies of BSR-4 were established and classified into 54 virulence phenotypes.Of the 67 selfed progenies,4 were similar to the parental isolate,17 increased in virulence spectrum and 46 decreased in virulence spectrum.Eight of the progeny were highly pathogenic but showed necrosis and a few of flecks and the other were highly pathogenic to Mingxian 169 and Guoluo.Based on differential host set for the barley stripe rust,the progeny were grouped into four pathotypes,one was similar to parental isolate and the other three increased virulence spectrum.Totally,30 selfed progenies of BSR-5 were produced with 22 various phenotypes.Different segregation of avirulence and virulence and mode of gene action at different loci were found.All the progeny showed highly susceptible symptoms in Guoluo and Mingxian169.Virulence spectra of progeny isolates on the barley differential sets was consistent with the parental phenotype.Phenotypes of the progeny were consistent with the parental isolate and all of the progeny were highly pathogenic to Guoluo and Mingxian169.This study indicated that the isolate virulent to both wheat and barley produce obvious virulence variation and virulence differentiation after sexual selfing.This provides a basis for the occurrence of stripe rust in the regions where wheat and barley are grown and susceptible barberry exists.