Effect of Neutralized Phosphorus Acid on Powdery Mildew and Fruit Quality of Muskmelon (Cucumis melo L.) in Greenhouse

Abstract

Greenhouse-grown muskmelon (Cucumis melo L.) is one of the most high value fruit crops in Taiwan. Powdery mildew, caused by Podosphaera xanthii, can infect leaves and vines of muskmelon and result in huge loss of quality and yield. In this study, the efficiency of two concentrations (1 and 2 g L^(-1)) of neutralized phosphorus acid (NPA) applied at two spraying schedules (7- and 14-day intervals) on controlling powdery mildew were compared with triflumizole and a water control in greenhouse. Disease severity of powdery mildew among different treatments were evaluated every 7-d after fruit set. The fresh weight of fruit, flesh thickness and total soluble solid content were evaluated as fruit quality index after harvest. When NPA was applied at a 7-d interval, the efficiency on controlling powdery mildew were not significantly different (P = 0.05) with triflumizole. In contrast, when NPA was applied at 1 g L^(-1) at 14-d interval, the disease severity was not significantly different with the non-treatment control. Overall, the 7-d spraying schedule has a better control on powdery mildew no matter what concentration of NPA was applied. In the fruit quality analysis, NPA sprayed at 2 g L^(-1) at 14 days and 1 g L^(-1) at 7 days significantly increased the fresh weight of fruits when compared with untreated control. However, there was no significant differences (P = 0.05) between treatments on the flesh thickness and total soluble solid content of muskmelon except for applying NPA at 2 g L^(-1)/14-d in the second trial.