genetic diversity of some melon and cantaloupe genotypes infected with fusarium wilt via antioxidant enzymes activity

fusarium wilt disease is one of the major plant diseases that affect melon production. in this study a total of 23 landraces and breeding lines of melon were collected from different regions of iran planted in a randomized complete block design with three replications and were studied to find new sources of resistant ones in the tray contained clay, pith mass and perlite in greenhouse. the root of seedlings after reaching at one to two true leaf stages were placed in a high inoculum concentrations of 1×106 spores per ml of fusarium oxysporum f. sp. melon for 3-4 min and then, roots were wounded. root samples from infected plants of all sensitive, semi-resistant and resistant genotypes were taken to examine biochemical changes for 8 days after 2 days of transplanting in 5 times and were kept in −80°c. the root of control plants dipped in tap water. the activity of peroxidase (pox, ec 1.11.1.7), polyphenol oxidase (ppo, ec 1.14.18.1), catalase (cat, ec 1.11.1.6), superoxide dismutase (sod, ec 1.15.1.1) and phenolic compounds (pcs) were measured. area under disease progress curve and disease severity were studied to identify relationship between disease resistance and enzymatic composition. the results of analysis of variance showed that infection of melon seedling with f. oxysporum race 1.2 led to many biochemical changes. the level of antioxidant defensive enzyme and pcs content increased in response to infection by the fom 1.2. the activity of pox, ppo, sod, pcs and cat in different genotypes approached to highest level at 4 days after inoculation. in clustering of cultivars via ward method, 32 landraces clustered into three groups. principal component analysis diminished all of variables to two components with 96% cumulative variances. isabelle and shadegani 2 landraces had the maximum genetic distance together. the isablle and shadegani 2 were identified as the most resistance and the most susceptible genotypes, respectively. the isablle, zard eyvanakey, charentais fom1, japalizi and maghasi placed in the same group. therefore, by crossing between these land races, the basic population could be obtained to study the gene action and to identify the effective gene(s) regarding tolerance to fusarium wilt.