Population Structure And The Source Of Puccinia Striiformis F.sp.tritici In Jiangsu And Zhejiang Provinces In 2019

Wheat stripe rust,caused by Puccinia striiformis f.sp.tritici(Pst),is an airborne and destructive fungal disease on wheat in many countries and regions of the world.In China,the disease generally occurs in northwestern and southwestern regions and sporadically in the Jiangsu and Zhejiang costal epidemiological region(JZER).In the 2019 spring,wheat stripe rust occurred seriously in this region,developed about one month longer than regular years,resulting in severe yield loss.However,the rust inoculum sources for the JZER costal epidemiological region remains unknown.Therefore,this study was to reveal the inoculum sources to JZER by combined methods of both phenotyping and genotyping for analyzing compared the genetic structure and gene flow of Pst populations from JZER and other provinces.It provides a theoretical basis for the management of wheat stripe rust in this region and even the whole country of China,and is of important meaning for guiding safe production of wheat.Herein,171 Puccinia striiformis f.sp.tritici isolates collected from 10 provinces including Jiangsu(JS),Zhejiang(ZJ),Anhui(AH),Gansu(GS),Guizhou(GZ),Henan(HN),Hubei(HB),Sichuan(SC),Shaanxi(SA)and Yunnan(YN),were phenotyped with the Chinese differentials and the monogenic lines differentials,and genotyped with 20 pairs of KASP-SNP primers.Based on the analysis of phenotyping and genotyping data by population analysis software,the inoculum sources and the dispersal pathways causing the epidemic in JZER were determined.The main results were as follows:1.The population structure of Pst isolates from JZER was highly similar to that from the northwest oversummering region,the key overwintering region and the southwest epidemiological region,but there were differences in population structure between Pst populations from JS and ZJ.Phenotype tests on the Chinese differentials indicated that shared races(CYR32 and CYR34)were detected in JZER population and those from the northwest oversummering region(GS),the key overwintering region(HB,HN,and SA),and the southwest epidemiological region(YN,GZ and SC).The dominant races in Pst populations from JS and ZJ were CYR32 and Su11-139 respectively,and those between the two provincial populations were different.In addition,races CYR32,G22-14,G22-68 were detected in JS population,but not in ZJ population,and Su11-208 was identified in ZJ population,but not in JS population.Cluster analysis of phenotypic data based on monogenic lines differentials showed Pst populations from JS and ZJ were classified into different branches,indicating that both population structures were different.2.Genotyping analysis based on KASP-SNP markers revealed Pst populations from JS and ZJ had similar level of genetic diversity,representing a high genetic diversity.But both Pst populations were genetically distant from each other,and quite low gene flow between the two provincial populations was detected,indicating that there were significant differences in genetic structure.Remarkable gene flows amongst populations from JS,YN,HN,and AH,as well as those from ZJ,GZ,and SC were detected.Gene flow among Pst population from GS,and those from HN and HB were detectable.3.Combined analysis with the wind field,two different inoculum sources of Pst responsible to wheat stripe rust in the JZER region in 2019 were determined,which spread by wind through the southwest and northwest pathways.Southwest epidemiological region played a major role in providing inoculum to JZER in spring.The YN population mainly contributed to the wheat stripe rust in JS.The ZJ population mostly originated from SC and GZ.The key overwintering region(HN and HB)played a minor role in providing inoculum to JZER in spring.However,Pst is not able to oversummer but can overwinter in this region.Therefore,the inoclumn source of HN and HB populations were mainly migrated from the northwest oversummering region(GS)in last autumn.The inoculum overwintered in this region and then spread eastward together with the main inoculum in southwest epidemic region(YN,GZ and SC),resulting in the occurrence of wheat stripe rust in JZER in 2019.Altogether,the occurrence of wheat stripe rust in eastern China in spring was caused by the simultaneous introduction of inoculum sources from northwest and southwest epidemiological regions.The results not only provide an insight into understanding the knowledge on wheat stripe rust epidemics in China,but also provide a new scientific basis for making strategy for the management of wheat stripe rust in China,which are of great significances in scientific research and agricultural practices.