PAN Yue-Min, YING Jin-Feng, GAO Zhi-Mou
Cotton Science. 2009, 21(1): 17-22.
Cotton red rot caused by Fusarium moniliforme seriously endangers cotton by causing the rot of buds, stem bases and roots of cotton at seedling phase, and resulting in boll rot in boll stage. The incidence and severity of the disease have been developing with the extending of Bt-transgenic cotton in the recent years in Anhui, China. In order to explore the population structure of the causal organism, the vegetative compatibility groups (VCGs) of the pathogenic fungus were tested by applying the nitrate nonutilizing (nit) mutant complementation technique. The isolates of F. moniliforme were isolated from cotton red rot diseased bolls collected from Xiaoxian, Chuzhou, Changfeng, Wuwei, Susong and Shexian in Anhui Province. The 12 tested single conidium strains obtained from the isolates above by single spore isolation were then transplanted on KPS plates to mutagenize nit mutants by referring to Correll′s method. After the tested cultures were incubated for 7 to 10 days at 25℃ in darkness, the fast-growing sectors and/or dot-form mutation colonies appeared. 232 nit mutants were recovered from the 12 single conidium strains of F. moniliforme by transferring chlorate resistant sectors from KPS medium to MM medium. The four mutant types named nit A, nit B, nit C, and nit D were obtained from different nitrogen media. Nit A was the most common type, which accounted for 77%. Next were nit B and nit C, with the rates of 11% and 10%, respectively. The least one was nit D, with the rate of about 2%. Nit A，nit B and/or nit C were selected to study vegetative compatibility of all isolates. The result showed that all isolates tested were divided into six distinctive VCGs. The isolates of CZ1, CZ2 and CZ3 belonged to VCG Ⅰ. The isolates of SX1, SX2 and SX3 belonged to VCG Ⅱ. The isolate of CF1 belonged to VCG Ⅲ. The isolate of SS1 belonged to VCG Ⅳ. The isolate of WW1 belonged to VCG Ⅴ. The isolates of XX1, XX2 and XX3 belonged to VCG Ⅵ. Complementation reaction occurred between the different nit mutant phenotypes derived from the same parental strain or different strain of the same VCG. Complementation occurred readily and reliably in nit B which was used to identify the vegetative compatibility group to which the tested isolates belongs. No complementation reaction was observed between any nit mutants recovered from the strains of different VCGs. The results mentioned above revealed the population structure of the causal organism and provided a special reference to the population genetics analyses and to the integrated control of cotton red rot caused by the fungus.
