Somsiri Sangchote and Araya Chaidee
Disease incidence of fruit rot, caused by Bipolaris cactivora, on dragon fruits obtained from Nakorn Ratchasima and Samut Sakorn provinces was at 4 and 14.7%, respectively. This pathogen was identified by its morphological characteristics and confirmed by molecular sequencing. It infected the fruit directly and through wounds. Conidia germinated and produced appressoria within 3 hours after inoculation under the moist condition at 25°C. Infection mycelia penetrated through cell junctions and stomatal openings. After three days, hypha had extended both intracellular and intercellular. Later, conidiophores and conidia were formed on the infected area. Dipping conidia of B. cactivora in hot water at 55°C for five minutes reduced conidial germination by 97.4%. Postharvest treatments by dipping in hot water at 51, 53 and 55°C for one minute showed fruit rot at 53.5, 49.1 and 44.8%, respectively. In vitro, PDA amended with difenoconazole at 37.5 ppm showed completed inhibition of mycelial growth of B. cactivora. Dipping the fruit in this chemical at the same concentration for one minute at ambient temperature showed complete control of fruit rot. The chemical residue in the fruits treated with difenoconazole at 37.5 ppm for 1 min was 0.07 mg/kg after stored at 25°C for five days.