Studies On Epidemiology Of Wheat Stripe Rust (Puccina Striiformis West.) And It's Ecological Control In Sichuan Province

Sichuan is considered as the inoculum sources of(Puccinia striiformis Westend f.sp.tritci Eriks.) in autumn and the main region where the inoculum can multiply continuosly in the whole winter.The inoculums spreading from oversummering areas with upper air can reproduce large number of uredia in winter-reproductive area in Sichuan basin through the whole seasons of winter and spring,which spread abroad to other winter wheat growing areas as the main sources of inoculums in the spring. Consequently,Sichuan has been considered as the hotspots for the disease epidemic circle and the disease management in China.The control of wheat stripe rust in Sichuan can protect the local wheat production and alleviate control pressures in other witer wheat growing areas.The inoculum of P.striiformis f.sp.can oversummer and also overwinter in Northwest Sichuan area,where susceptible wheat varieties were on mountains of different altitudes so the pathogen cycles between the wheat plants as well as volunteer seedlings at different altitudes with the help of wind.This area is also the refuge for the new races of the pathogen to develop.Therefore,wheat stripe rust usually occurred severely in the autumn,new physiological races of pathogen usually emerged firstly and the resistance of wheat varieties was liable to change in Northweat Sichuan. From the development history of physiological races of P.striiformis f.sp.tritici,we can see that the variance of pathogen in Sichuan affected the occurrence of wheat stripe rust greatly in local and other wheat growing areas in China.To study the epidemiology of the disease,the change of physiological races,the change of the resistance of wheat varieties and ecological control are of great importance to the forcast of the disease and sustainable control of the disease.Although great efforts had been paid to the epidemiological survey of the disease in Sichuan in the past 20 years,epidemiology of the disease had changed due to the global warming and changes in cultivation system and variety distribution.The time of disease emergence on the autumn seedlings of wheat had become earlier than ten years ago and longer epidemic period and higher severity of the disease had been observed in the whole growing seasons.The data collected from 132 counties were analyzed using GIS technology in order to reveal the epidemic characters of the disease and dispersal routes of the pathogen.The results indicated that Sichuan province could be divided into four epidemic zones of wheat stripe rust based on the ecological conditions,climate characters,disease occurrence and spreading as well as the systems of wheat production. i.e.,over-summer area in Northwestern Sichuan,over-summer and winter-reproductive area in Southwestern Sichuan,winter-reproductive area in Sichuan basin and spring epidemic area in South-east Sichuan.Pathogen inoculum of stripe rust could be spread by four dispersal ways along Min River,Fu River,Tuo River and Jialing River in the direction from north to south and from west to east in Sichuan province.The relative data analyzed showed that the resistance in wheat varieties,the incidence occurrence areas in winter,and climate factors in the winter and spring were the three major factors to affect the severity of the disease epidemics in the spring.Seedlings of 58 wheat cultivars and elite breeding lines were inoculated with 28 selected different isolates of P.striiformis f.sp.tritici to postulate the stripe rust resistance genes.The results showed that Yr1,Yr2,Yr3,Yr5,Yr7,Yr9,Yr10,Yr24,YrVir1-2,YrAlba and YrSu were detected in 42 wheat cultivars and beeding lines,either alone or in combination.Yr2,the most common gene,presented in 11 cultivars,while Yr10 in 9 cultivars.14 wheat cultivars were resistant to all the 28 isolates of Puccinia striiforms f.sp.tritici and may contain the Yr24 genes.10 wheat cultivars contained unkown genes or their combinations.Study on physiological races in Sichuan province showed that CY31 was the most dominant race during 1996～2000.Since 2001,occurrence frequency of CY32 exceeded CY31 and CY32 had become the most dominant race.Segregation in the Hybrid46 and Suweon 11 pathotype groups became more obviously.Occurrence frequency of the two pathotype groups with strong pathogenecity and wide virulence spectrum kept stable about 80%since 1997,especially in the past two years up to 99% in 2006 and 2007.Occurrence frequency of Hybrid46 pathotypes delined in the recent years whereas that of Suweon 11 ascended.Among Suweon 11 pathotype group, occurrence frequency of Su-14(CY33) rose obviously in the recent years,which had become the second dominant physiological race in 2007(18%).Virulence frequnency of pathogen colony to Yr3b+4b ascended year after year,especially to YrSu obviously. Virulence frequency to YrSu had up to 100%in 2007,being higer than that to Yr3b+4b.Intercropping and cultivar mixtures could increase species diversity which would keep ecological system stable and increase the system's functions.To study ecological control of wheat strip rust by intercropping of wheat and faba bean,field studies were conducted at 3 locations representing different ecological regions.The results showed that wheat strip rust was controlled by 31.4%～82.3%and the leaf spot of faba bean was controlled by 9.9%～26.4%by wheat and fababean intercropping.Wheat stripe rust dynamic developments of all-planting and mixed-planting had been systematically investigated in this study by taking different mixed-planting combinations among 6 wheat varieties(Chuannong 10,Mianyang 31,Chuannai 107,Chuanmai 37,Chuanyu 16 and Chuanyu 18)with different resistance levels.The results of this experiment showed that planting of four or six variety mixtures with different resistant level can delay the occurrence of wheat stripe rust,slow the speed of disease and decline the damage of disease as well as stabilize yield of wheats.Highly susceptible wheat varieties Mingxian 169 and Chuannong 10,slow-rusting variety Chuanmai 107,moderately resistant varieties Chuanyu 18,Chuanmai 37, Mianyang 31,and highly resistant variety Chuanmai 36 were sown in pot individually or in mixture and inoculated with a field sporadic virulent mutant to Chuanmai 36, which was belonged to pathotype Su-12 for consecutive propagation of the uredia.After 9 consecutive generations,uredia from each variety or variety mixtures were found to be virulent to larger numbers of Chinese physiologic race differential varieties.While uredia collected from Chuanmai 36 were found to be stably virulent to Chuanmai 36, such virulence was lost in the uredia from some varieties after 9 generations.Uredia collected from Chuanmai 36 and Mianyang 31 after 9 consecutive generation was identified as CY32 and Su-14(CY33),respectively to the most dominant race in Sicuan province.The number of compatible differential varieties to the uredia after 6 and 9 consecutive generations on Chuanmai 36 were also found to be higer than other that on other varieties and variety mixtures.The virulence of uredia in terms of the number of compatible differential varieties from 4 variety mixture containing Mianyang 31, Chuanmai 36.Chuanyu 18 and Chuanmai 107.was weaker than that of Mianyang 31 and Chuanmai 36 after 9 consecutive generations,whereas the virulence of the uredia from the mixture with 2 additional varieties.Chuanmai 37 and Chuannong 10.had been than that from Chuanmai 36 and Mianyang 31 since 6th consecutive generation.The uredia from the latter mixture after 9 consecutive generation failed to infect Chuanmai 36,suggesting the deleterious effects of variety mixture on the virulence enhancement of the pathogen.The primers which have been proved to demonstrate the AFLP of genomic DNA of P.striiformis f.sp.tritici in Sichuan failed to detect such polymorphism among the uredia collected from different varieties after 3,6 and 9 consecutive generations of propagation.