First report of soft rot of wax gourd caused by Pectobacterium carotovorum subsp. brasiliense in Japan and control effect of copper bactericides

A severe postharvest rot of wax gourd fruit shipped from Miyakojima, Okinawa Prefecture was reported in 2006. Although the fruit was healthy at the time of harvest, the disease caused its insides to liquefy during storage, and subsequently, the fruit softened and rotted. Entire colonies of white circular hygrophilous bacteria were isolated from nutrient agar containing the rotten section of the fruit. The rotting symptoms could be reproduced on wounding the fruit prior to inoculation of the isolated bacteria, and their pathogenicity was observed against sixteen plants across four families, including squash, eggplant and cabbage. Based on bacteriological characteristics and result of PCR analysis using specific primer pairs, all bacterial isolates were identified as Pectobacterium carotovorum subsp. brasiliense. This is the first report of wax gourd soft rot disease in Japan. Seedling inoculation of the isolated bacteria was assessed and preventive effects of copper bactericide against this disease were analyzed. The results of these analyses showed that copper (II) hydroxide wettable powders exerted a greater preventive effect than basic copper sulfate wettable powders. Further, inoculation test in the field showed that two rounds of spraying of the former during the fruit enlargement period resulted in significant preventive effects against post-harvest outbreak.