| Wheat stripe rust,caused by Puccinia striiformis f.sp.tritici(Pst),is one of the most devastating diseases on wheat.The disease is widely distributed,highly epidemic frequency in China,and causing frequently significant wheat yield losses resulting from the disease epidemics.Planting resistant cultivars is the most effective method of prevention and control of stripe rust,but“breakdown”of wheat resistance due to rapid virulence variation in the Pst population.CM42 is the original V26 isolate separated from the field sample of Pst in sichuan province.Field detect that virulence to Yr26 has increased in frequency in recent year and has high population genetic diversity,which may be connected with sexual reproduction.Since the discovery of Berberis spp.as the host of Pst,it has been possible to study sexual reproduction and genetic variation.In this study,we studied the effect of sexual reproduction on the occurrence of wheat stripe rust and the inheritance of Pst through the selfing of a original V26 isolate(CM42-2)on Berberis shensiana,and to explore virulence variation mechanism of V26 isolates and genetic differentiation regularity and to provide effective information for the prospective disease breeding,and then to improve strategies for a comprehensive improvement of wheat stripe rust in China.The main results of this study are as follows:Berberis shensiana was inoculated with germinal teliospores of CM42-2 isolate.After artificial selfing and aecium production,191 selfed progeny isolates were successfully obtained from 71 different aecial cups.Parent and 94 progeny isolates of different genotype were tested on 21 Yr near isogenic lines(NILs)of wheat for virulence/avirulence and 92R137(Yr26)for pathogenicity.All isolates were avirulent to Yr5 and Yr15,but all virulent to Yr25,Yr44.Progeny isolates were separated in other 18 virulence sites,and the P values of virulent/ avirulent separation were ranging 0.079 to 0.905.Segregation on Yr10,Yr17,Yr29 and Yr4 fit a model that single dominant gene control avirulence gene.However,segregation onYr2 and YrExp2 indicated that a single dominant gene control virulence.The rest of 12 virulent/avirulent sites were controlled by two genes.Avirulence/virulence on the Yr6,YrTye,YrA and Yr26 showed approximately 7:9,showing that avirulence could be controlled by two pairs of recessive genes overlap or independent control.Avirulence on Yr8,Yr43,Yr28 and Yrv23 might be controlled by two dominant genes,and one of them is suppressor.On Yr9,YrSp and YrTr1 sites,parent was avirulent,but the ratio of 1 avirulence: 15 virulence occurred on progeny,indicating that two recessive genes independent controlled the virulence on these sites.Parent was virulent while 15 virulence: 1 avirulence appeared on Yr31,indicating that two recessive genes independent controlled the avirulence.The above results indicate that virulence could be controlled by a pair of genes,and also could be two pairs,avirulent genes could be dominant or recessive.Sixty-seven virulence phenotype were identified based on 21 Yr NILs and 92R137(Yr26).virulent spectrum of 7 progeny was same as the parent,while virulent spectrum of 31 progeny isolates(33.0%)was wider than the parent.This indicated that sexual reproduction could produce new pathogenic types,and some pathogenic types had stronger virulence than the parent.Ninety-four multilocus genotype were produced from 191 selfed progeny isolates after analyzing by 13 pairs of polymorphic SSR markers.The correlation between the virulence and SSR of 94 progeny isolates was analyzed.The correlation coefficient between them was 0.127.Therefor,it can regard as no linkage between the virulence locus and SSR molecular marker,and there were mutually independent.The study of three single aecial cup found that 30 isolates separated from aecial cup SAC58 produced 13 virulence phenotypes(VP)by 22 identification hosts,of which VP1 contained 17 isolates.And 9 MLGs were produced after assay with 6 pairs of SSR markers with polymorphism,of which MLG 2 and MLG 3 included in 9 and 13 isolates,respectively.Similar results were obtained for the analysis of aecial cup SAC19 and aecial cup SAC8.Between virulent and molecular data suggested that isolates from a single aecial cup were not exactly identical,but the difference of isolates from same aecial cup were less than different aecial cups.Genetic analysis of a new Pst showed that sexual reproduction could produce new virulence phenotypes and new genotypes,and showed higher diversity.Therefore,we should develop a new strategies of barberry treatment techniques for the purpose of cutting sexual reproduction of Pst,and to reduce the rate of mutation of Pst and curb the spreads to protect the safety of wheat production in China. |
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