Roles Of Poaceous Grasses And Barberry In Occurrence Of Wheat Stripe Rust And Virulence Variation Of Puccinia Striiformis F. SP. Tritici

Wheat stripe rust, caused by Puccinia striiformis f.sp. tritici(Pst), is one of the most important diseases on wheat. It can spread for a long distance from its origin by air current, and was characteristic of reliable outbreak due to its epidemics, resulting in huge yield losses or even no grain. Therefore, this disease is most destructive biotic threat to wheat in China.Breeding and cultivating wheat resistance cultivar is most economic and effective approach for control of wheat stripe rust. However, the resistance of wheat cultivar was overcome by appearance of new race of Pst and cannot continue to be used. It was showed that virulence variation is the essential reason resulting in emergence of new races.The wheat stripe rust pathogen is strict biotrophic fungus, relying on living host for survive and reproduction by urediospores as major spore to cause reinfections. It infects wheat and many gramineous grasses. Although relationship between the grasses and the wheat stripe pathogen in China were made a little progress, it has not been clear so far. Therefore, it is necessary to make their relationship clear for occurrence, dissemination and integrated management of wheat stripe rust in China.Production of new race due to virulence variation is most factor causing epidemics of wheat stripe rust. Previous studies demonstrated that mutation,somatic combination and sexual reproduction can result in virulence variation. However, sexual reproduction of Pst has not been known until more recently. In recent years, as barberry serving as alternate host for Pst, many of barberry species were identified to be alternate host for Pst. It was found that, under natural conditions, Pst complete sexual cycle on wild barberry in China.In this study, based onisolation and virulence tests of Pstthat were derived from gramineous grasses with stripe rust infections in Gansu as hot-spot areas for Pst, and from barberry with aecial infections under natural conditions in 2013, it provided important theoeritical basis for uncovering mechanic of formation of variable area for Pstin oversummering regions and for making new strategy for control of wheat stripe rust. Major results were made as follows:1. The gramineous grasses are important hosts for oversummering of Pstand provide inoculums to cause autumn-sown wheat infections by stripe rust. Based on our investigations, it was general that the gramineous grasses were infected by stripe rusts in Gansu as an important oversummering area for Pst. These grasses include Poa annual,Elymus nutans, Agropyron spp., Cynodon dactylon and Elymus excelsus, had a percentage of 1.57%, 3.82%, 22.22%, 6.78%, 22.22% in Pst, respectively.2. Three hundered and elevenstrains were randomly selected to reinoculate four grass species, Poa annua, Elymus nutans, Agropyron spp., and Elymus excelsus. The infections on respective grasses were successful and produced a few teliospores except Agropyron spp..At the same time, Pst races, CYR33, CYR32, CYR31, CYR29, CYR23, and CYR17, were artificially inoculated on leaves of Poa annua, Elymus nutans, Agropyron spp., and Elymus excelsus, and only CYR29 race successfully infect Poa annuaand Elymus excelsus.3. More evidences of sexual reproduction of Pst under natural conditions were obtained in this study, suggesting that barberry plays a role in disease cycle of wheat stripe rust. Sixteen Pst samples were recovered from 9297 aecial samples from six barberry species, including Berberis brachypoda, B. soulieana, B. aggregata, B. shensiana, B. polyantha, and B. atrocarpa, which were collected from Gansu, Shaanxi, Tibet, and Xinjiang provinces. Two of the 16 Pst samples were matched with known race CYR32 in virulence pattern.4. Under natural conditions sexual reproduction of Pst cause obvious virulence variation to produce new races. Of the 16 Pst samples, two were CYR32 and the other 14 were new race(pathotype). Single uredial populations of the 16 Pst samples produced 88 pathogenicity patterns based on identifications on single Yr gene lines.Theresults showed that virulence of CYR32 differentiated on single Yr gene lines, suggests that identification ability of Chinese differential hosts is questionable.The identification results of single Yr gene lines showed that the single uredial strains seperated from Berberis had no virulence detected for Yr5,Yr10 and Yr15. Virulence to Yr Tr1, Yr24 and Yr27 were extremely low(< 3%); those to Yr SP, Yr9, Yr28, and Yr2 were low(13.6-28.0%); those to Yr7, Yr17, Yr8, and Yr Exp2 were moderate(33.1%-48.3%), and those to Yr6, Yr44, and Yr25 were high(52.5%-72.9%).