Bitter gourd (Momordica charantiaL.) is an important cucurbitaceous plant in which the deleterious diseases namely vascular wilt, damping off occurs commonly and causes 30 to 50 percent losses in crop. The present investigation was aimed to study the morphological and molecular characterization of disease causing pathogen to understand the etiology of the disease.Survey was conducted at different locations of Coimbatore, Erode and Dharmapuri and samples were collected for the isolation of the pathogen. The pathogen was isolated from the brownish discoloured vascular tissue of stem portion which was typically wilted. Pathogenicity assay was proved and the virulence of the fusarium isolates were identified under artificial inoculation studies. The morphological studies of Fusarium isolates were studied using the microscopic observation to study the micro and macro conidial variation.The molecular confirmation of pathogen was done by PCR amplification using ITS 1 and ITS 4primer at Ì´Ì´ 560 bp. The different species of Fusarium solani, Fusarium equiseti, Fusarium falciforme, Fusarium chlamydosporum and Fusarium incarnatumwere identified in these molecular studies. Among the species, Fusarium solani is a major pathogen associated with bitter gourd wilt disease. The genetic variability studies among different Fusariumspp. was carried out using RAPD marker. The variability studies revealed that virulence isolates viz, F. solani VP, F. solani EL, F. solani TP, F. falciforme IJ and F. chlamydosporum TN were grouped into cluster II which are more virulent and the same results were shown in pathogenicity. The wilt pathogen of bitter gourd isolated from the palee hybrid was shown more virulence when compared to the other isolates.

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