| Wheat stripe rust,caused by Puccinia striiformis f.sp.tritici.(Pst),is one of the most serious large scale fungal diseases of wheat.Generally,the outbreak of wheat stripe rust can cause approximately 10 to 30% of wheat yield lost.Growing resistant cultivars is the most effectively,economically,and environmentally friendly way.However,the virulence of Pst varied frequently,so the resistance of cultivars was often overcome by new Pst races when it released.The sexual reproduction has been proved to the most important ways of Pst virulence variation.There is a large number of sexual reproduction under natural conditions in China,especially.Therefore,to monitor the dynamic changes of Pst races are very essential under natural conditions in China.Since 1966,the Yr5 resistance gene has been identified as remaining resistance to all known Pst race worldwide.In 2017,we collected and identified Pst isolates with virulence to the Yr5 resistance gene in Guancun,Xinjie Town,Baoji City,Shaanxi Province.Identification of the Yr5-virulent isolate indicated that the Yr5 resistance gene may gradually lose resistance.The use of wheat cultivars(lines)with Yr5 resistance gene singly in wheat breeding is essential for being avoided.To clarify the potential threat and epidemic trend of the Yr5-virulent isolate and its mutants or derivatives,a series of studies were conducted.Therefore,the objectives of this study were(1)to evaluate virulence of Yr5-virulent isolates,(2)to assess the resistance of Chinese wheat cultivars to Yr5-virulent isolates,(3)to detect parasitic fitness,(4)to understand sexual reproduction of the Pst TSA-6 isolate via selfing on barberry in order to understand virulence variation and genetic diversity of the fungus,and to predict potential Pst progeny derivatives.1.Emerging races of Pst(TSA-1～ 10)with virulence to the Yr5 resistance gene were the first reported in China.Yr5-virulent isolates showed widely virulence spectrum and high virulence characteristics base on a set of 25 Yr single gene lines and 19 Chinese differential hosts set,with only a little Yr single gene lines showing different infect reaction.Among them,TSA-3,TSA-6,and TSA-7 were virulent to Triticum spelta album cultivar,while the other 7were avirulent.2.The Yr5-virulent isolates have a potential threat to Chinese major wheat cultivars.The Yr5-virulent isolates had highly pathogenicity to 165 major Chinese wheat cultivars.The Yr5-virulent isolates and.had similar virulence patterns with the Chinese currently dominant races(CYR32 and CYR34),base on a set of 25 Yr single gene lines.Among 165 wheat cultivars,109(66.06%)and 104(63.03%)of the cultivar inoculated with Yr5-virulent isolates were susceptible(S)or slow-rusting(SR)to TSA-6 and TSA-9,respectively.There is a significant difference in the pathogenicity of TSA-6 and TSA-9 to Chinese wheat cultivars between the seedling and adult stages(P<0.01).Only a little Chinese wheat cultivars carrying Yr genes,and most cultivars only containing one Yr gene.Among the 165 wheat cultvars,resistance genes Yr5 were postulated in 9(5.45%)wheat cultvars.3.The Yr5-virulent isolates might develop into an epidemic dominant race due to its high parasitic fitness.Based on principal component analysis(PCA)method,the results showed that the first component category representing sporulation capacity explained 45.62%,the second component category representing infectivity and spore survivability 26.64%,and the third component category representing expansion and potential infection ability 20.22% of parasitic fitness variation.Based on the establishment of extracted three principal components and a comprehensive factor score mathematical models,evaluations of the parasitic fitness attributes of tested races showed that the level of relative parasitic fitness of the tested six races was: CYR32(1.15)> TSA-9(0.95)> TSA-6(0.92)> CYR34(0.29)>CYR31(-1.54)>CYR33(-1.77).4.The sexual genetic variation of Yr5-virulent isolates is complex,with a high virulence variation rate and rich genetic diversity.120 progeny isolates were obtained by selfing the TSA-6 isolate on B.shensiana.They were divided into 73 virulence phenotypes on 25 Yr single gene lines.Only VP7 contains 3(2.5%)progeny isolates with the same virulence phenotype as the parental isolate TSA-6,with a variation rate of up to 97.5%.Compared with the virulence phenotype of the parental isolate TSA-6,22(18.33%)progeny isolates had increased virulence,72(60%)progeny isolates had decreased virulence,the remained 23(19.17%)progeny exhibited phenotypic differences from TSA-6 at one or two resistance loci.The virulence phenotype of progeny segregated at 21 Yr resistance loci;4 Yr resistance loci were homozygous.All of the selfed progeny isolates showed different segregation ratio at avurilence(A)and virulence(V)on 21 of Yr loci.The virulence phenotype was controlled by a single dominant or recessive gene at Yr2,Yr3,Yr5,Yr7,and Yr8 loci.The virulence phenotype was controlled by two genes at the Yr44,Yr76,Yr43,Yr Exp2,Yr1,Yr6,Yr9,Yr17,Yr25,Yr27,Yr28,Yr29,Yr SP,Yr32 and Yr Tr1 loci.These regulatory genes can interact in various modes,such as complementarity,inhibition,overlap,or independent effects.24 polymorphic KASP-SNP molecular markers were used to divide 120 progeny isolates into 118 multi locus genotypes(MLGs).A linkage map with a genetic distance of 624.5 c M was constructed with those markers.The avirulent gene Avr Yr5 was located within the 9 c M genetic interval between the markers KASP 458 and KASP 359 through QTL mapping.This study confirmed that Yr5-virulent isolates has a high pathogenicity to 165 Chinese major wheat cultivars,and has a higher parasitic fitness compared to Chinese current dominant races.Moreover,the sexual inheritance of TSA-6 isolate was complex,and the avirulence and virulence phenotype of different resistant loci were controlled by single or double genes,which conforms to Mendel and Morgan genetic model laws.In summary,the results of this study provided a new way to identify durable resistance for sustainable control of wheat stripe rust. |
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