Enzymatic Activities and Secondary Metabolite Contents in Roots of Melon Genotypes Infected with Fusariumoxysporum f. sp. melonisRace 1

Melon (Cucumismelo) production is significantly affected by Fusarium wilt worldwide. The pathogen, Fusariumoxysporum f. sp. melonis race 1 (Fom1) causes serious economic losses in Iran. To find resistance sources of melon, 45 local genotypes and breeding lines, collected from different parts of Iran, were screened against race 1 of Fom. Seedlings were inoculated with a suspension of 1×106 conidia/ml at first true leaf stage. The severity of the disease was assessed on leaves using a rating scale from 0 to 4. Analysis of variance demonstrated highly significant differences between the genotypes. Five susceptible and five resistant genotypes were inoculated with the causal agent and root samples were taken for 8 days. The activity of polyphenoloxidase (PPO)enzyme, phenolic compounds (PCs) and cucurbitacins content of the samples were analyzed to identifypossible relations between resistance and enzymatic activities. PPO activity and PCs content inresistantgenotypes significantincreased in response to infection by the pathogen, but there were not significant differences in susceptible genotypes. Analysis of variance showed that there was a direct relation between cucurbitacins D with resistance to the disease, while there was no clear relation between the content of cucurbitacins E with disease resistance.