Postharvest fruit rots of kiwifruit (Actinidia deliciosa) in Korea

Abstract

The overall disease incidence of postharvest fruit rots of kiwifruit (Actinidia deliciosa) in Korea averaged 32%, but the incidence ranged from 5% to 68% in the orchards surveyed. The percentage of kiwifruit showing internal and external symptoms were 21.9% and 4.9%, respectively, and an additional 5.2% of the kiwifruit showed both internal and external symptoms. Botryosphaeria dothidea and Diaporthe actinidiae cause ripe rot and stem‐end rot, respectively, and were identified as the major postharvest pathogens with average isolation rates of 83.3% and 11.9%. Incidence of the postharvest fruit rots was closely correlated with ripening temperatures favourable to the mycelial growth of the major pathogens. Postharvest fruit rots occurred at all ripening temperatures 11°C and maximum disease incidence was observed at 29°C. No mycelial growth of B. dothidea and D. actinidiae occurred on potato dextrose agar plates under 11°C and the optimum temperature ranges for mycelial growth of the pathogens were 26–35°C and 26–29°C, respectively. The optimum kiwifruit ripening conditions for minimising damage from the postharvest fruit rots were a 20‐day ripening at 17°C. Intensive application of fungicides just before or after the rainy season is conducted to control postharvest fruit rots in kiwifruit orchards of Korea. Benomyl WP and thiophanate‐methyl WP, registered as preventive fungicides against postharvest fruit rots, are usually applied 5–6 times at 10‐day intervals beginning in early June in the kiwifruit orchards. Tebuconazole WP, iprodione WP, and flusilazole WP were selected as alternative fungicides to prevent emergence of fungicide‐resistant strains and reduce the number of fungicide applications. The optimum spray programme for controlling postharvest fruit rots was four applications at 10‐day intervals from mid June for tebuconazole WP, iprodione WP, and flusilazole WP, compared with five applications for benomyl WP and thiophanate‐methyl WP.