The Population Structure Of Fusarium Spp. From Wheat In Sichuan Province

Fusarium head blight (or wheat scab) has been a serious disease of wheat around the world. The disease caused by Fusarium species reduces crop yield and the quality of grain by contaminating it with mycotoxins. Fusarium head blight is one of the three important diseases of wheat in Sichuan. To determine population structure of Fusarium species causing head blight of wheat, and to provide the scientific base for forecasting, controlling and resistance breeding, we conducted the research and collected wheat samples showing symptoms of Fusarium head blight from 12 area 26 cities and counties in Sichuan province in 2002-2004. The results of the research showed as follows:A total of 345 isolates were identified to be seven Fusarium species according to Nirenberg and Booth classification standards. There were Fusarium graminearum (94.5% isolates), Fusarium avenaceum (2.61% isolates), Fusarium moniliforme (0.87% isolates), Fusarium tricinctum (0.58% isolates), Fusarium equiseti (0.29% isolates), Fusarium culmorum (0.29% isolates) and Fusarium nivale (0.29% isolates). And F. graminearum was the predominant species in Sichuan province.The pathogenicity test was conducted on wheat in field. One hundred and two strains representing seven Fusarium species and forty-tree nitrate nonutlizing mutant strains were inoculated on wheat at flowering stage with the fungal inoculum. The pathogenicity were assessed by counting the number of diseased spikelets and divided into three scales: strong, medial and weak pathogenicity. The results shown that all tested strains including seven species of Fusarium could infect the ear of wheat, but there were some differences inseriousness. This difference suggested that the tested strains had pathogenicity difference. Among the seven Fusarium species, F. graminearum and F. nivale were strong pathogenicity; F. culmorum were medial pathogenicity; F. avenaceum, F. moniliforme, F. tricinctum and F. equiseti were weak pathogenicity. The most of strains of F. graminearum were strong (46.59% strains) and medial (50% strains) pathogenicity. The strains of weak pathogenicity were very rare (3.41% strains). The pathogenicity of F. gramineanim strains had no correlation with origin. When the nitrate nonutlizing mutants strains were tested, their pathogenicity were higher^ lower or similar to the wild-type isolates' and the lower ones were in the majority.Vegetative compatibility group of F. graminearum isolates was determined using nitrate nonutilizing mutants. Nitrate nonutilizing mutants were generated by placing isolates onto KPS and MMC media containing 1.5% chlorate. Among 85 isolates, 42 isolates produced nit mutant, which were recovered by transferring the chlorate-resistant sectors on MMC media to MM media containing nitrate as single nitrogen source. Among 1093 mutants, 404 mutants (36.96%) utilized both nitrite and hypoxanthine (nit\), 654 mutants (59.84%) utilized hypoxanthine but not nitrite (nit3), and 35 mutants (3.2%) utilized nitrite but not hypoxanthine (nitM). A nitl mutant from each isolate was pared on nitrate medium to either a nitM or nit3 from all isolates. 13 isolates that nitM mutant generated were identified self-compatible. No complementation was observed between any nit mutant recovered from the strains in different regions except the complementation between nit mutants from MS22-9 and MS22-6. Forty-two isolates were grouped into fourteen different VCGs at least. The results revealed that isolates of F. graminearum from Sichuan province were highly diversed in terms of vegetative compatibility group.