Molecular Evidence Of The Dispersal Of The Wheat Stripe Rust Pathogen From West To East In Central Shaanxi And Its Inoculum Source

Wheat stripe rust,caused by Puccinia striiformis f.sp.tritici(Pst),is an airborne disease.The pathogen is an important fungus that affects wheat and some cereal crops.Pst can spread its urediospores by air currents,causing inter-regional dispersal of the pathogen and occurrence of wheat stripe rust in wheat growing regions around the world.Through field investigation of the occurrence time of wheat stripe rust,it speculated that Pst could spread from the west to the east within central Shaanxi,and that the pathogen in Gansu could serve as the inoculum source to central Shaanxi.Whereas there is no direct evidence to support this hypothetical dispersal route.In this study,we investigated the genotypes of Pst isolates from different populations of central Shaanxi and Gansu province,analyzed genetic structure of overall population and gene flow between subpopulations,and clarified the spread route of Pst in central Shaanxi and the transmission relationship between both regions.The results provided a theoretical basis for the control of wheat stripe rust disease in Shaanxi province and the eastern wheat production regions of China.In the current study,321 Pst isolates collected from central Shaanxi and Gansu province in the 2019-2020 and 2020-2021 winter wheat cropping seasons were genotyped using 23 pairs of KASP-SNP markers.Based on combined methods for various population genetic studies,we analyzed the relationship between subpopulations and clarified spread route of the wheat stripe rust fungus within central Shaanxi as well as the main spread route from Gansu province to central Shaanxi.The main conclusions were as follows:1.The migration of Pst between Gansu and central Shaanxi was mainly from Gansu to central Shaanxi,and there was gene flow of Pst populations between the two regions.The subpopulations of central Shaanxi and Gansu province showed a high level of genetic diversity,and similar population genetic structure.There was a certain degree of gene flow between subpopulations of the two regions,with a low degree of genetic differentiation.2.Pst in central Shaanxi was migrated from west(Baoji)to east(Weinan).Genetic exchange between the four subpopulations of central Shaanxi was frequent(5.559 ≤ Nm ≤29.148),with a low degree of genetic differentiation(0.009 ≤ Fst ≤ 0.043).3.The inoculum source of wheat stripe rust in central Shaanxi was mainly introduced from Longnan and Tianshui areas of Gansu province in 2019-2021,and minorly from Pingliang and Qingyang areas.Analyses of population structure and gene flow of Pst in central Shaanxi and Gansu province indicated that the genetic distance between Longnan and Tianshui areas of Gansu province and central Shaanxi was closer than Pingliang and Qingyang areas.While,common genotypes were found between Longnan and Tianshui of Gansu province and central Shaanxi,but not between Pingliang and Qingyang areas and central Shaanxi.4.Linkage disequilibrium analysis showed that a strong genetic recombination existed in Pst populations of Baoji and Xianyang areas of central Shaanxi and those of Longnan,Tianshui,Pingliang and Qingyang areas of Gansu province,which may cause the increase of genetic diversity.In summary,the present study provided molecular evidence that Pst spread from west to east in central Shaanxi,and showed that Gansu(especially Longnan and Tianshui)was one of the major origins of the pathogen inoculum causing wheat stripe rust in central Shaanxi.The results revealed the west-to-east spread route of wheat stripe rust in central Shaanxi,i.e.,Baoji→ Xianyang → Xi’an → Weinan.This study provided a basis for interrupting the transmission of stripe rust between Gansu and Shaanxi,and for the occurrence and control of wheat stripe rust in China.