| Stripe rust,caused by Puccinia striiformis f.sp.tritici(Pst),is one of the most important fungal diseases in wheat(Triticum aestivum L.)worldwide,and often results in high yield losses.Host plant resistance is the most effective means to control stripe rust,hence,planting resistant cultivars is recommended.However,resistant cultivars apply significant selection pressure on the pathogen to cause rapid shifts in pathotypes.Consequently,these changes in the Pst pathogen can make previously resistant cultivars become susceptible.Therefore,it is important to monitor changes in pathogen population virulence from different resistant cultivars and compare genetic diversity differences among Pst populations.In this study,a total of 394 isolates of Pst were collected from five wheat cultivars(Mingxian169,Zhengmai9023,Xiaoyan22,Mianmai367 and Xikemai4)at Yanting county and Fucheng district,Mianyang city of Sichuan province in China from 2014 to 2015.Additionally,components of parasitic fitness of cultivar-race combinations of stripe rust were determined.The main results obtained are as follows:1.The stripe rust population from Sichuan basin exhibited high diversity with a complex virulence structure.A total of 25 races were identified and characterized from 196 stripe rust isolates collected during 2014 through 2015 from five wheat cultivars in Yanting county in Sichuan province.The most frequently identified pathotype in 2014 and 2015 was G22 group(race group virulence for Guinong22(Yr26).No isolates virulent to Zhong 4(Yr+)and Triticum spelta album(Yr5)were found.Components of parasitic fitness of pathotype G22,CYR32 and CYR33 of Pst were determined in 109 wheat cultivars(lines)collected from Sichuan Province in the field.Relative parasitic fitness of different cultivar-race combinations was calculated according to the observed values of infection type,prevalence and severity.The average relative parasitic fitness value of pathotype G22 is significantly higher than that of CYR32 and CYR33 at the population level(P<0.01).Due to its high parasitic fitness,pathotype G22 is becoming the predominant race in Sichuan province.2.Isolates of Pst from different wheat cultivars showed differences in the composition of races,distribution frequency,and diversity.The relative Shannon's index(HSR)among populations has the difference,from high to low is Xikemai 4(0.711),Mingxian 169(0,690),Zhengmai 9023(0.655),Xiaoyan 22(0.640)and Mianmai 367(0.579).There was a high genetic variation within populations from five wheat cultivars,but a lower genetic differentiation among populations based on virulence factors(?pt=0.018,P=0.031).Populations genetic diversity were analyzed with SSR markers in 394 single-pustule isolates of Pst,obtained from five wheat cultivars.The results showed genetic diversity level have difference among populations.Genetic diversity was highest in population on Mianmai367,a high resistant variety.3.The effects of simulated acid rain on fitness of Pst were investigated in this study.The results demonstrated that simulated acid rain could suppress the urediospores germination of Pst.Heavy acid rain(pH 3.5)significantly reduced the germination rate(P<0.01)of Pst and reduced the infection probability,which resulted in the extension of the latent period,the decrease of sporulation and the decrease of disease index.4.In this study,inter-simple sequence repeats(ISSR)technique has been successfully applied to development a sequence-characterized amplified region(SCAR)marker for diagnosis of stripe rust of wheat and detection of Pst.On the basis of full understanding of stripe rust pathogens composition of races,distribution frequency,and diversity,knowing their genetic structure characteristics and parasitic fitness,to provide a theoretical basis for integrated management of wheat stripe rust and effective deployment of resistance genes in Sichuan province. |
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