Study of genetic diversity of Fusarium oxysporum f.sp melonis based on VCG groups and ISSR marker

Fusarium wilt of melon is one of the most common disease of this crop in the world and specially Iran. Using resistant cultivars is still the most effective method of management of this disease. However, for screening cultivars for resistance, knowledge of genetic diversity of a fungal population is necessary. In this study, genetic diversity of the pathogen in Khorassan provinces was studied. twenty isolates of F. oxysporum, the causal agent of melon wilt was from Khorasan province (collection of the department of plant protection at Gorgan Agricultural university) have been selected and their genetic diversity was studied using VCG and ISSR techniques. For VCG method, At first nit mutants were generated on chlorate media and then nit mutants were assigned to different phenotypic classes on the basis of their growth on media containing one of the five different nitrogen sources (NaNO3, NaNO2, Ammonium nitrate, uric acid and Hypoxanthine). 68% of nit mutants were classified to nit1, 18% to nit3 and 14% to NitM phenotypic classes. In order to complete tests and determining VCGs, all NitM mutants of every isolate were paired with nit1 or nit3mutants of other isolates. As a result, among the isolates vegetative incompatibility were observed, and isolates were grouped into 20 VCGs. In addition, genetic diversity of theses isolates was studied using twenty primers. Cluster analysis of ISSR data using UPGMA method and SM’s coefficient distinguished 5 main groups at 60% similarity level. This results showed there was significant genetic variation among F. oxysporum f. sp. melonis isolates in Khorassan. On the other hand according to cluster analysis it was determined that there was no specific correlation between geographical regions and genotypic groups.