Virulence Variation Of The Progeny Derived From Sexual Hybridization Of Puccinia Striiformis F.sp.tritici Races PL17-7 And CYR32 And Construction Of AvrYr43 Genetic Population

Wheat is one of the most important food crops and cultivated widely in the world.Wheat stripe rust,caused by the fungus Puccinia striiformis Westend.f.sp.tritici Erikss.(Pst),is a major threat to the safe production of wheat worldwide.Planting stripe rust-resistant wheat varieties is the most effective,environmentally-friendly,and economic approaches for the control of wheat stripe rust.However,during wheat production,new virulent races often overcome the resistance of wheat varieties.Accumulation of new races and large-scale growing of an individual wheat variety can be apt to cause outbreak of stripe rust,resulting in a huge yield loss.Recently,with the discovery of Berberis as alternate host for Pst,studies have been reported sexual reproduction can result in significant virulence variation,generating new races distinguishing from those of the parental isolates.For the rust fungi,sexual reproduction is mainly involved in selfing,hybridization of races,hybridization of formae speciales,and interspecific hybridization.So far,little is known about sexual hybridization of races and virulence variation and identification of avirulence genes of Pst has not been reported.In order to determine the role of sexual genetic recombination in virulence variation,identify avirulence gene of Pst,and reveal molecular mechanism of virulence variation,in this study,sexual hybridization of Pst races of CYR32,a predominant race,and PL17-7,a highly virulent race,was conducted.Avirulence and virulence patterns of the progeny derived from sexual hybridization of both races were identified on single Yr gene differentials and analyzed their virulence variation compared to the both parental races.Simultaneously,genetic population of Avr Yr43 was established by the cross of the two Pst races and inheritance analysis of the avirulence gene locus was performed.The genetic population provide research materials for further identifying Avr Yr43.The main results were as follows:1.Determination of avirulence and virulence characteristics of Pst races CYR32 and PL17-7 to resistance genes loci.CYR32 was virulent to Yr43 and PL17-7 was avirulent to Yr43.Rust tests on single Yr gene differential hosts showed that Pst race CYR32 was avirulent to Yr5,Yr8,Yr10,Yr15,Yr24,Yr26,Yr32,Yr SP,and Yr Tr1,showing homozygous avirulence.CYR32 was virulent to Yr1,Yr2,Yr3,Yr4,Yr6,Yr7,Yr9,Yr17,Yr25,Yr27,Yr28,Yr43,Yr44,Yr A,Yr Exp2 and Yr Tye,indicating homozygous virulence.Pst isolate PL17-7 was avirulent to Yr5,Yr6,Yr8,Yr15,Yr32,Yr43,Yr SP and Yr Tr1 and virulent to Yr1,Yr2,Yr3,Yr7,Yr9,Yr10,Yr17,Yr24,Yr25,Yr26,Yr27,Yr28,The Yr32,Yr44,Yr A and Yr Exp2.2.Avirulence and virulence characteristics of the progeny derived from the both Pst races were different at Yr gene loci and inheritance of the two races was distinguished.The total of 68 progenies was obtained from the cross of CYR32 and PL17-7 and tested their avirulence and virulence on the single Yr gene differential hosts,generating 24 virulence patterns.The progeny population was virulent to Yr1,Yr2,Yr7,Yr9,Yr17,Yr27,Yr44,Yr Exp2,Yr25,Yr28,Yr A,showing homozygous virulence,and was avirulent to Yr5,Yr8,Yr10,Yr15,Yr24,Yr32,Yr Tr1,and Yr26,showing homozygous avirulence.However,the progeny was heterozygous to Yr6,Yr43,Yr SP,Yr Tye,Yr18,Yr29,Yr3,and Yr4.Segregation of the 68 progenies was fit for a ratio of 1:3 at avirulence to virulence gene loci of Yr4,Yr18,Yr29,Yr43 and Yr Tye,indicating that avirulence genes at each of the five Yr gene loci were controlled by single recessive gene.A segregation ratio of 7:9(A:V)was identified at Yr6 and Yr SP,showing that the both gene loci were controlled by two dominant genes.Avirulence locus at Yr3 was controlled by two recessive genes based on a ratio of 1:15(A:V)against the resistance gene.3.Avirulence gene Avr Yr43 was controlled by single recessive gene.Based on tests of 221 progenies to Yr43 locus,inheritance of the progeny population showed that 62 progenies were avirulent to Yr43,and 159 were virulent to the locus.Segregation of the progeny population at Yr43 was fit for 1:3 of avirulence to virulence,showing that Avr Yr43 was controlled by individual recessive gene.The results in the present study showed that sexual hybridization between Pst races can result in remarkable virulence variation.Some of the progeny population were highly virulent than the parent races and the others were lower virulent than the parent races.Sexual hybridization between Pst races is an important way in resulting in virulence variation of Pst and was complex in inheritance.Avirulence gene loci can be controlled by one or two genes and avirulence genes interaction were multiple.