Activity of peroxidase and cucurbitacin D in melon genotypes following challenge by the fungal pathogen Fusarium oxysporum f. sp. melonis race 1

Abstract:Melon (Cucumis melo) production is significantly and economically affected by Fusarium wilt worldwide. Cucurbitacins are bitter tetracyclic triterpenoids that are toxic to most organisms and occur widely in wild and cultivated Cucurbitaceae. In order to study the effect of cucurbitacin D content and activity of peroxidase (POX) on the resistance of melon genotypes to Fusarium oxysporum, five susceptible and five resistant genotypes were inoculated with the race 1 of the causal agent. Root samples were taken daily from the inoculated plants for 8 days and were used for quantification of cucurbitacin D by High performance liquid chromatography. Analysis of variance showed that there was a direct relation between cucurbitacin D with resistance to the disease. No cucurbitacin D was found in susceptible genotypes in day 0 (no infection), but in resistant genotypes in the same period was higher than other days. Analysis of variance demonstrated a direct relation between cucurbitacin D with resistance to the pathogen. Although the POX activitiy in both groups increased in response to infection by the pathogen, this significant increase was more prominent in resistant genotypes. The enzyme activity approached to pick at 4 days after inoculation. The results suggested that the increased levels of POX activity in melon genotypes play an important role in the induction of resistance to this disease.