Study On The Cultural Characteristics And Pathogenicity Differention Of Defoliating Pathotype Strains Of Verticillium Dahliae In Different Cotton-producing Provinces

Verticillium wilt, one of the most important diseases of cotton in China, is extremely common in cotton-producing areas. Especially, the defoliating pathotype of Verticillium wilt threatens cotton quality and yield seriously. Though some so called resistant varieties have been breeded in some areas, its usually represent tolerant, even susceptible when these varieties were planted in production areas or introducted to other areas.There are a lot of reports about the cultural characteristics and pathogenicity differentiation of nondefoliating pathotype of Veticillium dahliae in cotton, but there is no systematic and synthetical report to defoliating pathotype of Veticillium dahliae in different cotton-producing provinces.The culture characteristics and pathogenicity differentiation of defoliating pathotype of Veticillium dahliae strains from the main cotton-producing areas in China had been studied, using root-dip method in greenhouse, and the relationship between cultural characteristics and pathogenicity of defoliating strains had been discussed, in order to provide some theoretical instruction for the identification of disease-resistant and breeding.1. Two primer pairs INTD2f/INTD2r and INTND2f/INTND2r were used to discriminate the defoliating and the non-defoliating pathotypes of Veticillium dahliae, respectively, detecting the pathotype of Veticillium dahliae by duplex-PCR assay from the main cotton-producing provinces. The results showed that32tested srains were belong to defoliating pathotype, the others were belong to nondefoliating pathotype. Defoliating pathotype strains accounted for88.9%among the tested srains, indicating that defoliating pathotype strains of Veticillium dahliae had already existed in all the main cotton-producing provinces.2. According to the assay of culture characteristics, defoliating pathotype strains could be divided into three types:sclerotium type, middle type and filamentous type. The majority of type was sclerotium type, accounted for93.8%; the strains with radialized and fold stripe were relatively more, accounted for68.8%among the strains of sclerotium type; dense mycelium strains accounted for63.3%among the strains of sclerotium type. The maximum average growth rate was0.16cm/d among ten cotton-producing areas, the minimum one was0.15cm/d, that meaned there was less difference among cotton producing provinces. The maximum average spore production quantity was in Hubei, the minimum one was in Jiangsu. The fluctuation range of the Yantze River Valley was bigger than the Yellow River Valley. The average spore production quantity between two valleies was5.10E+06A/ml. There was significant difference of spore production quantity between the Yellow River Valley and Yantze River Valley.3. The pathogenicity differentiation of32defoliating pathotype strains of Veticillium dahliae from ten main cotton-producing provinces were tested by the root-dip method in greenhouse. Four identified varieties were all upland cotton with different resistance. The results showed that the pathogenicity of defoliating strains were great different, and the32defoliating strains could be divided into five types at least according to the pathogenicity differentiation on the four identified varieties, average disease index of the type I strains was less than35.0, accounted for28.1%among all defoliating pathotype strains; the others were greater than35.0, accounted for62.5%. The pathogenicity of the strains from different cotton-producing provinces might be difference, the highest of average disease index was in Shandong, the lowest was in Henan; average disease index of nine provinces were greater than35.0. Severe defoliating strains in pathogenicity had already spread in all the main cotton-producing provinces. In addition, there was less difference between strains from the Yellow River Valley and Yantze River Valley.4. Correlation between the morphological characteristics and the pathogenicity was not obvious, the pathogenicity of dense mycelium strains were stronger than sparse mycelium strains, and there was no relations of defoliating strains between growth speed and pathogenicity. But there was negative correlation between production quantity and pathogenicity.