Parasitic Fitness Of Four Major Prevalent Races Of Puccinia Striiformis F.sp.tritici In China

The capacity of pathogenic fungi infection and development on host is most likely determined by the relative parasitic fitness of host-pathogen interactions. Twenty one important wheat cultivars including 17 widely feeding cultivars and two known Yrgenes were used as the testing materials to determine parasitic fitness of four prevalent races of wheat stripe rust (Puccinia striiformis f. sp. tritici, Pst) in China, namely CYR32(Chinese yellow rust, CYR), CYR31, Su11-14 and Su11-4. A total of fourteen parameters in the disease development process was selected for test, and the data were statistically analyzed by the factor analysis in SAS statistical software. The results indicated that disease capacity was the most important component of parasitic fitness, as well as urediniospore vitality , sporulating capacity, sporulating area and sporulation period were secondly important, leading to conclude that the relative parasitic fitness of the pathogen could be determined by spore yield of uredia×infection probability×uredium density×percentage of germinating urediniospores/latent period Percentage of germinating urediniospore, infection probability, latent period , uredium pustule density and spore yield of uredia are most important parameters in different stages of disease development, e.g. penetration period, incubation period, and expansion period.The relative parasitic fitness of 4 races as CYR32, CYR31, Su11-14 and Su11-4 was analyzed and the results showed that CYR32 displayed the highest relative parasitic fitness, larger virulence spectrum, the highest spore germinating percentage, highest infection probability, shorter latent period, most more spore yield of uredia, highest sporulation and uredium density among all of the four tested races tested, which was the reason why it became the most predominant race at present. Comparatively, Su11-14 possessed of higher parasitic fitness than CYR31 on 12 wheat cultivars tested. It suggested that Su11-14 would become a predominant race in the near future, and should be paid more attention to monitor its virulence evolution and dynamics. Since 2000, the frequency of CYR 31 have decreased anually, it can be explanation for low parasitic fitness. Aalthough the frequency of Su11-4 was increasing, it needs quite some time to become dominant race because its parasitic fitness is also low.Virulence spectrum of four races were tested on 39 near-isogenic lines or gene-known lines. The results showed that CYR32 contained 19 virulent genes, while both Su11-14 and Su11-4 contain 14 virulent genes Yr genes. CYR31 contained 12 virulent genes, In addition, CYR32 can be virulence for 16 Chinese domestic differentials, and Su11-14 virulence for 15 domestic differentials, while CYR31 and Su11-4 can infection 14 and 13 domestic differentials respectively.