RAPD Analysis Of Wheat Powdery Mildew (Blumeria Graminis F.sp.tritici) Populations And Genetic Analysis Of Avirulence Genes

Eighty-nine progeny isolates from a wheat powdery mildew cross of El 6 X E25 were tested on differential hosts in greenhouse. The results show that avirulence matching Pm3d is controlled by three recessive avirulence genes. Each of avirulences matching Pm3b and Pml9 is controlled by two recessive avirulence genes. One gene controls virulence matching Pm4a and Pm4b, respectively, and Aw4a and Avr4b are found to be linked with a recombination rate of 1.1%.On the basis of genetic information about the avirulence genes, we looked for RAPD markers related to them using bulked segregant analysis. 180 arbitrary primers were used in the analysis but no targeted bands were found. A band of about 2.0 to 2.5kb was obtained with primer OPD03 using the genomic DNA of the avirulent parent E25, and it was absent in the products from virulent parent El6. About half of the progeny had this band but there was no apparent correlation between the band and the virulence of the progeny. We guess that this band is associated with mating type gene or with a gene determining an unknown phenotype.Eighty-four isolates from Hubei, Jiangsu, Beijing, Henan, Shandong, Shanxi were tested in RAPD analysis of the fungal populations. Genetic distance and identity among isolates and populations of wheat powdery mildew were calculated according to the RAPD results using Nei's function. Mean genetic distance between isolates is 0.3382, and the mean identity is 0.7249. This shows the high genetic diversity in the mildew pathogen. The mean genetic distance between populations is 0.0321 and the mean identity is up to 0.9685. This suggests that they have a common center of origin. There may be long distance migration between the regions. Clustering analysis show that populations from Hubei and Henan are grouped together, those from Beijing, Shandong and Shanxi form another branch, and Jiangsu is included at the last node. No close relationship is found between the clustering anlysis results of mildew populations according to RAPD results and the virulence of isolates.