Development And Genetic Anaylsis Of Sexual Population And Avirulence/virulence Genes Of Puccinia Striiformis F.sp.tritici

Wheat stripe rust,caused by Puccinia striiformis Westend.f.sp.tritici Erikss.et Henn.（Pst）,is an important wheat plant disease that seriously threaten safety of wheat production in the world.Annual strip rust epidemic can cause an average of approximately 30%of wheat yield loss,and complete failure of wheat in the outbreak years.Selection and breeding of disease-resistant wheat varieties can be considered an effectively,economically and environmentally friendly way for control of occurrence and prevalence of wheat stripe rust.However,the resistant of wheat varities are often overcome by new virulent races of the stripe rust pathogen within a few years since released,resulting in failure of resistance genes and causing the disease pandemics.Mutation,somatic hybridization and sexual reproduction are major ways to cause virulence variation of Pst.Recently,barberry were found as an alternate host for Pst.After sexual selfing of Pst under controlled conditions,Pst can produce a large number of new isolates carrying different virulence loci,which directly proved that sexual reproduction of Pst on barberry as alternate host plays a key role in virulence variation of the stripe rust fungus.In China,existence of sexual cycle on barberry bushes of Pst was discovered in the nature based on recovery of many new isolates with different virulences from rust-infected barberry.This indicated that barberry as major alternate host for Pst play important roles in epidemics and virulence variation of Chinese Pst population.Investigating the virulence structure and pathogenic variation in sexual population of Pst could be favor for understanding inheritance mechanism of avirulence/virulence genes,which were very useful for wheat breeding program and developing long-term resistance wheat cultivars to Pst races.Thus,in this study,we first focused on sexual reproduction of CYR32by selfing on barberry to know virulence genetics.Then we developed a population were established by a cross between CYR32 and Pinglan 17-7 of Pst races on barberry under controlled conditions for avirulence/virulence genetic analyses.Major results were as follows:1.A total of 127 single-aeciospore isolates were obtained through a race CYR32 that selfed on barberry to complete sexual reproduction.Twenty seven pathotypes were found among the selfed progeny based on 25 Yr single gene lines used as differential hosts for differentiating virulene.The progeny isolates and the parent race CYR32 were all avirulent to Yr5,Yr8,Yr10,Yr15,Yr24,Yr26,Yr32,and YrTr1 loci;and virulent to Yr1,Yr2,Yr3,Yr4,Yr25,Yr44,and Yr76（YrTye）loci.However,virulence of the progeny were segregated on Yr6,Yr7,Yr9,Yr17,Yr27,Yr28,Yr43,YrA,YrExp2 and YrSP loci.2.All of the selfed progeny showed different segregation ratio at avurilence/virulence on10 of Yr genes loci.The ratio of 1:3 were detected on Yr7,Yr28,Yr4 and YrExp2 loci,1:15 on Yr6,Yr9 and YrA,3:13 on Yr17 and Yr27;9:7 on YrSP,respectively.These results revealed that virulence of CYR32 to Yr7,Yr28,Yr4 and YrExp2 was controlled by a dominant gene,virulence to Yr6,Yr9 and YrA was controlled by two independent dominant genes,virulence to Yr17 and Yr27 was controlled by one dominant and one recessive gene,and that the avirulence to YrSP was controlled by two complementary dominant genes.3.The 127 progeny isolates were classified into 65 multi-locus genotypes by using 10polymorphic SSR markers.Linkage map was constructed based on 27 virulence phenotypes and 65 genotypes involved two linkage group.The first linkage map consisted of ten avirulence genes and one SSR marker.The genetic distances between two neighboring virulence loci was ranged from 2.36 between avr6 and avrA to 39.87 cM between avrExp2and AvrSP1.The secod linkage composed of nine SSR markers.4.Sexual hybridization of CYR32 and Pinglan 17-7 generated 14 progeny isolates that were classified into 3 virulence phenotypes based on tests on 23 Yr gene lines,and none phenotype was the same as both parental races.All of progeny isolates were avirulent to Yr5,Yr8,Yr10,Yr15,Yr 24,Yr 26,Yr 32 and Yr Tr1 and virulent to Yr1,Yr2,Yr7,Yr9,Yr17,Yr25,Yr27,Yr44,Yr28,YrA and YrExp2.The progeny differed from phenotype on Yr4,Yr6,Yr43and YrSP.5.A F₂ sexual population of 245 isolates was developed by selfing of a F₁ isolates on barberry.Virulences of the progeny population were significantly separated on Yr10,Yr24 and Yr26 and ratio of avirulence to virulence was close to 9:7,indicating that avirulence of Pst against Yr10,Yr24 and Yr26 were controlled by two complementary dominant genes.