The Migration Pattern Of Puccinia Striiformis F.sp.Tritici In China And The Spread Of The Pathogen Between Pakistan And Chinese Populations

Wheat stripe rust,caused by Puccinia striiformis f.sp.tritici（Pst）,occurs worldwide and is a destructive disease that affects wheat production in China.The disease can spread a long distance by air,causing sever epidemics that can result in the damage and yield reduction.China is the largest epidemic of wheat stripe rust globally and has the characteristics of remarkable uniqueness and complexity.Understanding countrywide pathogen population structure and inter-epidemic region spread of wheat stripe rust are crucial for deciphering occurrence of disease in China.This study aimed to understand the population structure and migration route of Pst across China and the role of southwestern epidemics in occurrence of wheat stripe rust countrywide based on sampling from 15 provinces representing six epidemic zones,viz.Over-summering,Overwintering,eastern,Yun-Gui,Xinjiang,and Tibet epidemic Regions.Meanwhile,this study also compared China and Pakistan Himalaya region populations and access pathotype and virulence diversity from major epidemic regions of China.Main results were as follows:1.It was determined that southwestern epidemic region plays a role in occurrence of wheat stripe rust in China.The results of this study revealed high genotypic diversity in Oversummering,Tibet,and Overwintering epidemic regions.Geographical and epidemic regions partly explain population subdivision with variable divergence(F_ST=0.005 to 0.344).Xinjiang and Tibet epidemic regions were independent epidemic zones with the least sharing of genotypes.Among the other epidemic zones,i.e.,southwestern-Central,eastern,and northwestern epidemic zones,re-sampling MLGs,clustering-based Structure,DAPC analyses,and low divergence(F_ST from 0.006 to 0.073)revealed frequent geneflow.Yun-Gui epidemic regions,with a potential for both over-summering and overwintering,could play an important role in causing rust epidemics in main wheat-cultivating areas of China.2.It was testified that Chinese and Pakistan populations of Pst are independent and gene flow occurs within respective Pst population.There was no shared multilocus genotype between Pakistan population（Gilgit-Baltistan,Hazara and Azad Jammu Kashmir）and Chinese population（Xinjiang,Qinghai,Tibet,Sichuan,Guizhou and Yunnan）.A clear divergence was observed between bordering regions of Pakistan and China(F_ST=0.28)without any resampling of genetic groups and multilocus genotypes.The closest subpopulations across two regions were Xinjiang and Gilgit-Baltistan（Nei’s distance=0.147）,which were close geographically.A very high diversity and recombinant population structure was observed in both populations,though slightly higher in China（Genotypic diversity=0.970;r（?）d=0.000）than Pakistan（Genotypic diversity=0.902;r（?）d=0.065）.The distribution of genetic groups and resampling of MLGs revealed more geneflow across Yunnan,Guizhou and Sichuan regions in China,while between Hazara and Azad-Jammu Kashmir in Pakistan.The lack of gene flow for a long-distance migrating pathogen between two regions due to the Himalaya Mountains as natural geographical barriers blocking this process.3.It was identified that pathotype and virulence diversity of Pst population from some regions of China.Totally,163 isolates from Gansu,Guizhou,Sichuan,Shaanxi,Tibet,Qinghai,Hubei and Yunnan region of China were multiplied and tested against 18 Avocet Yr lines.Virulence frequency was lower against resistant genes Yr5,Yr10,and Yr32（less than 20%）.Virulence Yr5 was missing in Gansu,Guizhou,Hubei,Qinghai,Shaanxi,Sichuan while present in Tibet and Yunnan locations.Virulence Yr 10 is missing in Shaanxi,Tibet,and Yunnan locations,and Yr 15 is absent in all sites.The results showed similar high genetic diversity and recombinant population in line with high virulence and pathotype diversity in Gansu and Yunnan.Altogether,the results as above indicated that inter-regional spread of Pst across China and the role of main epidemic regions in occurrence of wheat stripe rust in the whole country,which is importance of guiding management of wheat stripe rust and wheat breeding of improvement to the disease.