Parasitic Fitness And Genetic Diversity In Sexual Hybridization F₂ Of Setosphaeria Turcica

Northern corn leaf blight, caused by Setosphaeria turcica which is heterothallic fungus, is one of the important corn leaf diseases, which can lead to destructive damage to the corn in the epidemic years. The fungus can enhance its pathogenicity, increase its pathogenic host range and generate new physiological races through sexual hybridization. 32 sexual hybridization F2, whose parents were isolate 40 and 42, were obtained in this experiment. In order to be sure the relationship between the pathogenicity and genetic diversity, the parasitic fitness, mating type, AFLP and capillary electrophoresis were tested.The testing results of the parasitic fitness indicated that there were distinct difference between sexual hybridization F2 and their parents. Some sexual hybridization F2 were enhanced but others weakened in the parasitic fitness. Two special types were found that one type could cause necrosis spots in corn leaves but the abilities of producing conidiophore were very low or lost and another type neither induce necrosis spots nor pruoduce conidiophore after they were inoculated some sensitive hosts.All the 32 sexual hybridization F2 were examined for their mating type in the Sach medium. The experimental results showed that 31.25 percent of them were "A" mating type and 43.75 percent were "a" mating type, 6.25 percent were "Aa" and 18.75 percent F2 were neuter. The ratio was 81.25 percent that could produce perithecium after crossing with parents in the 32 sexual hybridization F2. Therefore, the mating type of the Setosphaeria turcica inclined to the bisexual, which increased the opporunity of the sexual hybridization and selectivity and it made the degree of the aberrance more complex.256 primers were designed and EcoRI-GG and MseI-GC were defined as the best primer in AFLP in this study. The results showed that all the sexual F2 offspring had specific AFLP fingerprint and abundant diversity in DNA level. The clustering map was maked out according to the strips on the polyacrylamide gel by NOSA5 software. The results indicated that there were 3 clusters when the distance was 19, in which 27 F2 were similar to their parents and the other 5 were different from their...