Influence of root exudates of watermelon on fusarium oxysporum f. Sp. Niveum
Watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai var. lanatus] production in the same field without rotation of crops leads to disease buildup and poor yields. The purpose of this research was to evaluate the influences of root exudates produced by watermelon cultivars susceptible or resistant to the pathogen Fusarium oxysporum f. sp. niveum (FON). At low concentrations of root exudates (<50 mg L–1), the susceptible cultivar stimulated the growth of FON but the resistant cultivars inhibited FON at high concentration (200 mg L–1). Mycotoxin production was increased more in the presence of exudates from susceptible than resistant cultivars and after flowering than before flowering. Activities of enzymes (protease, pectinase, cellulose, and amylase) were stimulated more in resistant than susceptible cultivars by FON. Also, there were higher ratios of antifungal phenolic acids (p-hydroxybenzoic, phthalic, gallic, coumaric, cinnamic, ferulic, salicylic, and sinamic acids) to fungus-stimulating phenolic acids (vanillic and syringic acids) in resistant cultivars than in susceptible ones both before and after flowering. Breeding of resistant cultivars containing more antifungal agents is a strategy that, if pursued, could lead to a reduction in the occurrence of watermelon wilt disease, especially when rotation of crops is not possible.