Characteristics Of Physiological Differentiation Of Strains (Fusarium Oxysporum) From Cucurbitaceous Crops

Fusarium oxysporum Schl is a worldwide soil-borne plant pathogenic fungus, having a number of host plants. Cucurbitaceous crops are important economic plants in Fujian province; however, Fusarium wilt has become a severe disease on cucurbitaceous crops with the enlargement of the cultivated area and the extension of establishment cultivation during recent years..20 isolates of F. oxysporum, from cucumber, melon and watermelon at Zhaoan and Yongtai, were selected to make the classification into formae speciales by detecting the activity ofβ-D-glucosidase, determining the pathogenicity and identifying the host. Moreover, systemic studies on the physiological differentiation of the fungi were conducted on the aspects of vegetative compatibility groups, sequences of rDNA-ITS regions and fatty acid methyl ester (FAME). The correlation between formae speciales and VCGs, rDNA-ITS or FAME were discussed, respectively.Through detecting the pathogenicity and testing the activities ofβ-D-glucosidase, F. oxysporum strains from cucumber, melon and watermelon in Fujian province were divided into three formae speciales: F. oxysporum f. sp. cucumerium, F. oxysporum f. sp. melonis and F. oxysporum f. sp. niveum.Phylogenetic analysis of 0-1 matrix and nit mutants were applied to identify the VCGs of F. oxysporum. The results showed that the strains were grouped into 7 VCGs, while F. oxysporum isolated from cucumber, melon and watermelon could be divided into 2 VCGs, 3 VCGs and 2 VCGs, respectively. The isolates of different formae speciales were grouped into different VCGs. while the isolates belonging to the same formae speciales might have more than one VCG. Nonpathogenic strains had no compatibility to pathogenic ones from the same host.The sequences between ITS1 and ITS2 of F. oxysporum isolates were sequenced. The results showed that the identity of the isolates belonging to different formae speciales were 100%. Hence, it was impossible to distinguish the formae speciales of F. oxysporum by rDNA-ITS.The fatty acids of the F. oxysporum were detected with Gas Chromatography (GC). The model figure of fatty acids of F. oxysporum was established and the change rule of fatty acid peak height was analyzed. The results showed that the available peaks had retention times from 1.651 to 16.200. Most of the isolates had four representative peaks from C14:0 to C18:0. The results of principal components analysis showed that the diversities of C14:0 and C15:0 might be used to differentiate the isolates. It was concluded that the FAME analysis could uncover the physiological differentiation phenomena of F. oxysporum. However, to apply FMAE on identification of the formae speciales of F. oxysporum, more experiments should be done.