Isolation And Identification Of The Wheat Stripe Rust Pathogen From Naturally Rust-infected Berberis

Stripe rust of wheat,caused by an obligate and biotrophic fungus Puccinia striiformis f.sp.tritici(Pst),is one of the most destructive diseases of wheat in the globe.The disease distributes widely in China and its pathogen population represents a high diversity,complexity of genetic polymorphism.A large scale epidemic of the disease resulted in a huge yield loss,seriously threating safe production of wheat in China.Growing wheat cultivars possessing resistance genes against the disease is considered as the most economic,low-cost,and environmental-friendly method for control of the disease.However,the resistance of wheat cultivars was overcome by the emergence of new Pst races within a few years since their released,leading to wheat susceptible and following outbreak of stripe rust on wheat.The previous studies thought that the main reason for the loss of resistance of wheat cultivars was the appearance of new races of Pst because of virulence variation of the pathogen.It also thought that mutation,heterocaryosis,and somatic recombination contribute to pathogen variation and gave rise to new races.Sexual reproduction is important of quickly producing new virulent races via to genetic recombination,playing a role in genetic diversity of the pathogen.However,more recently,sexual stage of Pst was discovered and it demonstrated that the pathogen is a marcrocyclic rust fungi with five types of spores including urediospore,teliospore,basidiospore,pycniospore and aeciospore in the whole life cycle.This finding makes possible to study on sexual reproduction.There is a wide geographic distribution of barberry(Berberis)and a large number of barberry species in China.Barberry bushes growing around wheat fields are very common in many regions of China,especially northwestern and southwestern China as oversummering areas for Pst.At present,recent studies showed that Pst completes sexual on barberry as alternate host under natural conditions in China.However,the study on function of barberry in production of new races of Pst is needed and is important of efficient control of wheat stripe rust.Therefore,the objectives of the present study were to isolate Pst samples from naturally infected barberry,establish their single-uredium populations to test their virulence based on the Chinese differential set,and analyze their virulence patterns,and to confirm the role of sexual reproduction on barberry in pathogenicity variation of the wheat stripe rust fungus.The results were as follows:1.We isolated 8 Pst samples from 3 Berberis spp.collected from Gansu and Shaanxi provinces in 2015.Based on their virulence tests,only one Pst sample was matched to the known Pst race Su11-126 in virulence patterns,and the remaining 7 were new races.2.Among 47 virulence patterns produced from 93 single-uredium isolates,14 were known race types and 33 new race types,Fifty six out of 93 were matched with the known Pst races in virulence patterns and 37 were new.In this study,we obtained more evidences for supporting the existence of sexual reproduction of Pst on Berberis spp.in nature in China,leading to a fact that sexual reproduction of Pst regularly occurs under natural conditions.Our results confirmed that wild Berberis spp.play a role in completion of the whole life cycle of Pst and in disease cycle of wheat stripe rust in China.It provides an important theoretical basis for the long-term effective prevention and control of wheat rust in China,and also has an important guiding significance for production practice.