No abstract

No 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.

Pseudomonas syringae pv. actinidiae causes bacterial canker disease in kiwifruit. Owing to the prohibition of agricultural antibiotic use in major kiwifruit-cultivating countries, alternative methods need to be developed to manage this disease. Bacteriophages are viruses that specifically infect target bacteria and have recently been reconsidered as potential biological control agents for bacterial pathogens owing to their specificity in terms of host range. In this study, we isolated bacteriophages against P. syringae pv. actinidiae from soils collected from kiwifruit orchards in Korea and selected seven bacteriophages for further characterization based on restriction enzyme digestion patterns of genomic DNA. Among the studied bacteriophages, two belong to the Myoviridae family and three belong to the Podoviridae family, based on morphology observed by transmission electron microscopy. The host range of the selected bacteriophages was confirmed using 18 strains of P. syringae pv. actinidiae, including the Psa2 and Psa3 groups, and some were also effective against other P. syringae pathovars. Lytic activity of the selected bacteriophages was sustained in vitro until 80 h, and their activity remained stable up to 50°C, at pH 11, and under UV-B light. These results indicate that the isolated bacteriophages are specific to P. syringae species and are resistant to various environmental factors, implying their potential use in control of bacterial canker disease in kiwifruits.

No abstract