| Wheat stripe rust and barley stripe rust are caused by Puccinia striiformis f.sp.tritici（Pst）and Puccinia striiformis f.sp.hordei（Psh）,respectively.It is a devastative fungal disease that threatens the security of wheat and barley production.Studies showed that wheat stripe rust was a macrocyclic fungus and could complete sexual reproduction on the susceptible barberry plants.In northwest China,including Qinghai,Gansu,Shaanxi,Tibet and other province,it has been confirmed that Pst can complete sexual reproduction on barberry under natural conditions in spring.However,infection of Pst on alternate hosts in autumn has not been reported.In the highly altitude areas of northwest China,where the weather in autumn is similar to those in spring,it is not clear whether Pst can complete sexual reproduction by infection of barberry in autumn.Tibet is a relatively independent epidemic area of stripe rust in China.According to field investigation of our lab oratory,Berberis spp.is widely distributed in Tibet,while rusted barberry is common in autumn in this region.So,it needs to be confirmed that whether Pst can complete sexual reproduction by infecting barberry plants and provide aecidiospores for the occurrence of stripe rust in autumn in Tibet.It has been confirmed that Psh can infect barberry and complete sexual reproduction,however,after sexual reproduction,the genetic pattern and virulence variation of avirulence genes need to be further revealed.In addition,Pst and Psh have common alternate hosts of barberry.So,whether sexual recombination can occur among the two specialized types and produce new isolates on the same alternate hosts needs to be further studies.In Tibet,wheat and barley are mixed growing,stripe rust has been damaging the local wheat production all year round,and there are overlapping hosts of Pst and Psh.It is urgent to determine whether gene exchanges can occur between the two populations.In this study,to investigate whether Pst can complete sexual reproduction in Tibet in autumn,field investigation of barberry rusted was conducted,and inoculation of the rusted barberry leaves was carried out to obtain Pst isolates.Through phenotype and genotype analysis,the effect of Pst complete sexual reproduction on barberry in autumn on wheat stripe rust occurrence was determined.The selfing population of Psh was constructed to clarify its virulence genetic model.The effect of hybridization between specialized types on virulence variation was studied by hybridization between isolates of Psh and Pst.To explore whether there was gene exchange between Psh and Pst populations in Tibet,population structure and genetic diversity were studied on Psh and Pst isolates collected from 2018-2020.Main research results were as follows:1.Pst can infect barberry and complete sexual reproduction in autumn.In autumn,2016,rusted of barberry was investigated in Linzhi,Tibet.Sixty-five single-uredium isolates were obtained from collection samples of rusted barberry leaves,of which results showed virulence diversity on phenotype identification and new races took percentage of 67.69%.Based on SSR data,analyzation showed abundant of genotypes and high genetic diversity.Low level of linkage disequilibrium supported that the population is sexual（r?d=0.0-0.3;P=0.001-0.469）.2.The infected volunteer wheat seedling can provide Pst for autumn-sown wheat seedlings,and barberry rust had potential threat to volunteer wheat seedlings in Linzhi.In this study,comparation analysis on phenotype and genotype were conducted between populations of Pst isolates from volunteer wheat（76）,autumn-sown wheat（38）,and barberry plants（65）,which collected in Linzhi,Tibet,in October 2016.The results showed that common phenotype or similar phenotype existed in the three population,and high virulence diversity were detected between these populations.Population structure indicated that there was close relationship between the Pst isolates from volunteer wheat and the autumn-sown wheat（Nm=9.55）,and there was some gene exchange between Pst isolates from rusted barberry plants and the volunteer wheat（Nm=1.11）。3.Virulence genetics of Psh is complex and conforms to Mendel’s law of heredity.Sexual recombination is an important way for new races production.In this study,53 progenies were obtained through selfing a Psh isolate XZ-19-972 on B.aggregata.Virulence phenotype results showed that progeny had virulence or avirulence separation,and virulence variation of the progeny rate was high（81.1%）.Based on the 22 pairs of KASP-SNP markers,the progeny population showed abundant genotypes,and a linkage map of 516.07 c M was constructed.4.Sexual recombination between Pst and Psh is revealed,and increase the heterozygosity of progeny and the population diversity was enriched.Forty isolates of F1 were obtained by sexual hybridization isolates of 32B-2 and XZ-19-972 on B.aggregata.Isolate T-SAZ4 of F1was selected to construct F2 generation population,and 148 races were obtained.T-SAZ4 was heterozygous at all the 8 loci tested,and the progeny isolates showed virulence separation.Based on 22 KASP-SNP markers,the homozygous genotype loci were conformed to normal distribution,indicating that F2 isolates were randomly generated,and a linkage map of 496.3c M was constructed.5.Both Pst and Psh population were sexual in Tibet,and gene exchange existed among these two populations.In this study,during 2018-2020 in Linzhi,Tibet,120 and 140 P.striiformis isolates were isolated from wheat and barley,respectively,of which barley population,wheat population and mixed population were divided on host specific.Based on KASP-SNP data,high genetic diversity was detected in Pst and Psh populations,and gene exchange existed among the two populations.Linkage disequilibrium analysis supported that most sampling points（60%-76%）of the two populations were sexual（r?d=-0.333-0.393,P=0.004-0.847）.In this study,we confirmed that Pst can infect barberry and complete sexual reproduction in autumn,which had a potential threat to the epidemic of stripe rust on autumn-sown wheat in autumn in Tibet.Psh has complex virulence inheritance patterns and fit for Mendel’s law.Sexual recombination can occur between Psh and Pst,and it’s an important reason for the diversity of Puccinia striiformis on wheat and barley.In addition,gene exchange existed between Pst and Psh populations in Tibet.The results of this study will provide theoretical support for the prevention and control of stripe rust in the mixed sowing areas of barley and wheat,and provide theoretical basis for the formulation of the prevention and control strategy of stripe rust in China. |
