The Population Diversity And Genetic Structure Of Pyricularia Grisea In Sichuan

Rice blast is a important pathogen in Sichuan province. 123 strains of Pyricnlariagrisea were collected and 68 of them can infect Duoxi No.l .The result showed that the physiological races of the pathogen were composed of 6 groups involving 10 races and ZB group was dominant with a frequency of 64.5%,including 4 physiological races named 829,830,831332.Among ZB group,631 and 632 races were the most prevalent races with the total frequency of 30.8%.Analysis of mating type can provide an evaluation of genetic diversity of Magnaporthe grisea population. 141 strains of Pyricularia grisea from different districts of Sichuan province were studied for their mating type and fertility with standard strains KA3,GUY11 and 6023,2539w.The result indicated that 27 isolates were belonging to mating type MAT1-1 and 24 were belonging to mating type MATl-2.The fertile ratio of isolates was 36.2% on average .This suggested that the frequency of sexual stage occurrence of Magnaporthe grisea was low.According to the sequences of MAT1-1 and MAT1-2 genes of the fungus, two pairs of specific primers to the MAT1-1 and MAT1-2 alleles were useed, and the PCR thermal profile was also optimized as: initial cycle of denaturation at 95 for .5 min; 30 cycles of 30s denaturation at 94, 30s annealing at 54 , 1 min extension at 72; and final cycle of extension at 72 for 7 min. Furthermore, 32 isolates collected from rice field were mated with tester isolates GUY11 and KA3 and also tested by PCR. The result showed 75% of 32 fertile isolates were the same in mating type determined by the PCR amplified allele-specific fragments and mating with GUY11/KA3. This study indicated that PCR was applicable in assessment of M.grisea mating type, especially was capable of predicting the potential mating type of those sterile isolates in the natural population of the fungus.DNA fingerprints of 68 Magnaporthe grisea isolates from different sources which can infect Duo Xi No.l were tested using rep-PCR technique.Polymorphism of DNA amplified fingerprints appeared among the isolates .The number of DNA amplified bands varied from 2 to 19 in them .The isolates were clustered into 11 genetic lineages at 0.70 genetic similarity of which No3,7,10 groups were the dominant lineages. Non-obvious relation was shown to exist among the genetic lineages, the originat hosts of the isolates and their collected places.But the diversity of the strains which can infect Duo Xi No.l was obvious.