Study On The Epidemic Rule Of Wheat Stripe Rust In Qinghai Province

Wheat stripe rust caused by Puccinia striiformis f.sp.tritici(Pst)is one of the most important diseases threatening the security of wheat production in China.The long-distance transmission of the Pst uredinospores causes the regional epidemic of the disease.Understanding of the stripe rust epidemic is essential for the disease control.Qinghai is one of the most important Pst oversummering areas in northwest China which is closely adjacent to major endemic area of wheat stripe rust.Due to extensive cultivation of susceptible wheat cultivars such as Abel,Jingnong 411 and Plateau 448,stripe rust is endemic almost every second year in Qinghai,yielding an annual reduction of over 10%.In 2002 and 2007,the stripe rust epidemic hit more than 200 million mu and the yield loss was about 40%.With the warming global climate and the alteration of farming system,since 2000,under the expansion of winter wheat planting in the north China,winter wheat has been started to be planted in Qinghai province with an area of about 300,000 mu.The formed staggered planting of winter and spring wheat and vertical distribution of the three-dimensional layout have changed the prevalence of wheat stripe rust significantly.Therefore,in the present study,we intend to study the existence of the annual cycle of wheat stripe rust in Qinghai through survey on stripe rust disease in the overwintering and oversummering areas;clarify the virulent diversity among the Pst isolates based on the virulent phenotype analysis;reveal the Pst population genetic structure and the degree of inter-population differentiation in different regions in Qinghai province by SSR and SNP markers.Meanwhile,the role of barberry in epidemics of wheat stripe rust in Qinghai is studied.Combined with the high wind flow field and geographical environment,the epidemic of stripe rust in Qinghai province has been comprehensively studied.The main results are as follows:First,investigation of Pst oversummering in Qinghai province revealed that Pst can survive on the late-maturing spring wheat and volunteer wheat seedlings from the harvested winter wheat until late October,which maintained a large quantity of pathogen source for infecting seedlings of early sowing winter wheat.Compared with the past,the scope of oversummering expanded,the duration of oversummering extended and the Pst quantity of oversummering increased in Qinghai province.Second,monitoring of Pst overwintering in Qinghai province revealed that from 2013 to 2017,wheat stripe rust could normally overwinter in the winter wheat planting areas of Qinghai,but the overwintering rate of the infected leaves was low(less than 1%).The upper limit of altitude for overwintering of Pst was 2260 m.The general trend of overwintering for Pst was that the higher the altitude was,the lower the overwintering rate was.Meanwhile,the pre-winter Pst quantity,the mean temperature in January and the rainfall(snow)in winter as well as ecological environments are the factors that affect the ability of Pst overwintering and overwintering rates.Third,the population genetic diversity of Pst in Qinghai province(1)More abundant virulence diversity was observed in the Pst population in the initial summer epidemic than in the overwintering Pst population,with a gene flow value of 31.38.SSR and SNP molecular marker analyses showed that the genetic structure of the overwinter population and summer epidemic population with similar geographical locations were of high similarity,and that of initial epidemic of summer was higher.The meteorological data showed that from March to May the wind direction of the tested isolates collection area is mainly the northwest airflow and the south airflow,with partial southeast airflow from the southern Gansu to the eastern Qinghai via.The results showed that there was wide exchange between the overwintering population and the early summer population in Qinghai,and the overwintering Pst population was the main Pst source for the early summer epidemics,and also introduction isolates from other province.(2)The virulence phenotype analysis revealed no significant difference in the virulence diversity of Pst population on the winter wheat and spring wheat in 2016,with a gene flow value of 27.83.SSR and SNP analyses showed that there was little difference in genotype diversity of winter wheat and spring wheat population,and the Pst population on winter wheat and spring wheat with similar geographical position were of similar genetic structure.Meanwhile,the genetic diversity of Pst population on spring wheat was slightly higher than that on winter wheat.Meteorological data showed that the wind direction from June to August was mainly the southeastern airstream.Results above indicated that there was extensive exchange of the Pst population on winter wheat and spring wheat,and the Pst population on winter wheat played an important role in the epidemic of stripe rust in spring.(3)Analyses of the Pst population structure in different seasons.Study on the distribution frequency of virulence gene indicated that the genetic diversity of Pst population in autumn was relatively higher than that in spring and summer in 2016.SSR molecular marker analyses revealed that the gene flow value was 24.46 between Pst populations in spring and in summer,3.35 between Pst populations in spring and in autumn,and 4.07 between Pst populations in summer and in autumn.SSR and SNP analyses indicated the high similarity of population genetic structure in spring and in summer,and relatively low similarity of that in spring and autumn,The Pst population in summer and autumn shared similarity but still with significant difference.It seems that there is Pst exchanges between two consecutive seasons among spring,summer and autumn.(4)From 2014 to 2016,the spatial and temporal changes of Pst population structure showed of the varied virulence diversity in Qinghai province in different years,which was highest in autumn 2016,followed by 2014,and the lowest in 2015.The virulence frequency was 0 on Yr5 in three years,0.03 on Yr15 in 2015 and 0 in the other two years,0 on YrTr1 in 2016 and 0.03 in the other two years,and relatively high virulence frequencies on the rest 25 Yr genes.Fourth,transmission relationship of the Pst population between Qinghai and Gansu.(1)The virulence phenotype data showed that in 2016 spring,the virulence diversity of Pst population in Qinghai was slightly higher than that of Gansu,with a gene flow of 36.96.SSR and SNP data showed that in spring,the Pst populations in Qinghai and Gansu were of similar genetic structure,and in Qinghai the genetic structure of the primary epidemic Pst populations on winter wheat and the overwintering Pst populations were of high similarity.Combined with the wind field data from March to May,all the results suggested a high level of gene exchange between the spring Pst populations in Qinghai and Gansu,and that overwintering Pst played a role in the summer epidemic in Qinghai.(2)From 2014 to 2016,for the autumn Pst populations in Qinghai and Gansu of the same,little difference was observed in the virulence diversity,while relatively more significant difference among the three year.Population genetic analyses by SSR and SNP revealed that the genetic structure of the Pst population in autumn 2016 in Qinghai was slightly higher compared to that in Gansu,with a gene flow of 2.63.Based on the data of wind field of Qinghai,there is a certain exchange of Pst between Guide,Xunhua county in Qinghai province and Jishishan county in Gansu province.Most of the Pst isolates may be spread by wind from the southeastern Gansu to eastern China.Fifth,investigation on the geographic distribution and identification of Berberis spp.in Qinghai showed that six species(Berberis poiretii,Berberis vernae,Berberis dictyoneura,Berberis approximata,Berberis aggregata,Berberis circumserrata)are very general in geographic distribution,and could serve as alternate host for Pst.Sixth,Phenotypic and genotypic diversity of the two current epidemic Pst races CYR32 and CYR33 in China.Virulence and genotype characterization of 29 CYR32 and CYR33 isolates from 11 provinces revealed 17 virulence phenotype,exhibiting virulence variation on 9 Yr genes,including Yr2?Yr17?Yr27?Yr32?Yr43?YrSp?YrExp2?Yr28 and YrV23.From individual virulence phenotype,the majority of CYR32 and CYR33 isolates had differentiation on resistance genes Yr2,Yr17,Yr27,Yr32,Yr43,YrSp,YrExp2,Yr28,and YrV23.The virulence diversity index(K)of CYR32 and CYR33 isolates were 0.089 and 0.097,respectively.And the Shannon information indexes(I)were 0.44 and 0.45,respectively.At 0.93 similarity coefficient level,CYR32 and CYR33 were divided into five and eight virulence groups,while were clustered into ten and sixteen genotype groups with the similarity coefficient index of 0.84.The results showed that CYR32 and CYR33 with the same virulence characteristics on Chinese differential set have been differentiated on both virulence and genotypic characteristics in different regions.Taken together,this study comprehensively characterized the epidemic rule of wheat stripe rust in Qinghai province,which provides a new understanding on its role in the disease endemic areas in China.Furthermore,the obtained information will provide the necessary scientific information for stripe rust control in Qinghai oversummering areas,which is of great significance in the prevention and management of wheat stripe rust in Qinghai by controlling the initial Pst inoculum sources.