Enzymatic activities in roots of melon genotypes infected with Fusarium oxysporum f. sp melonis race 1

Melon (Cucumis melo) production is significantly and economically affected by Fusarium wilt worldwide. The pathogen, Fusarium oxysporum 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 x 10(6) 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 peroxidase (POX, EC 1.11.1.7), and polyphenoloxidase (PPO. EC 1.10.3.2), enzymes, and phenolic compounds (PCs) content of the samples were analyzed to identify possible relations between resistance and enzymatic activities. Although the POX and PPO activities and PCs content in both groups increased in response to infection by the pathogen, this significant increase was more prominent in resistant genotypes. The enzymes activity and phenolics content approached to pick at 4 and 6 days after inoculation, respectively. The results suggested that the increased activities of POX and PPO and PCs in melon genotypes play an important role in the induction of resistance to this disease. (C) 2011 Elsevier B.V. All rights reserved.