Genetic variation among 25 isolates of Fusarium oxysporum f. sp. lycopersici causing tomato wilt was determined using pathogenicity test and Amplified Fragment Length Polymorphisms (AFLP) markers. The isolates were collected from 8 provinces in Thailand. Based on the pathogenecity result, all isolates were divided into two groups as pathogenic and non-pathogenic isolates. Cluster analysis based on AFLP also grouped the pathogenic isolates into 3 subgroups as low, moderate and high virulence. A dendrogram resulting from a cluster analysis showed two main distinct groups: group 1, non-pathogenic isolates; and group 2, pathogenic isolates rooting from outgroup. Eighty one polymorphic bands were analyzed using computer software. The results showed that genetic differentiation occurred among populations (Gst = 0.5898). However, the populations in the same geographical areas, Khonkaen and Nong khai, Tak and Phechaboon were more closely related genetically than another populations based on Nei’s genetic distance, indicating the movement of the fungal conidia between these areas. This work provided new information on the formae speciales of F. oxysproum f splycopersici NKSC01 and NKSC02, of high virulent which could be classified as race 2 causing wilt of tomato var. Cheery.
Key words: Fragment length polymorphisms (AFLP) marker, tomato, pathogenecity,Fusarium oxysporum f. sp. Lycopersici.
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