Semi-commercial hot water treatments to control apple bull's eye rot (Neofabraea alba)

Bull’s eye rot (BER), caused by Neofabraea alba, is an important postharvest apple disease worldwide. Reduction of BER by application of hot water treatments (HWT) was demonstrated in laboratory studies on inoculated ‘Scilate’ apples. Application of a sanitiser (Tsunami) and UV-C did not provide significant reduction of bull’s eye rot, and did not improve HWT when used in combination. Warming fruit after 3 weeks coolstorage followed by replacing fruit in the coolstore reduced bull’s eye rot, but not as effectively as HWT. The feasibility of using HWT in a semi-commercial packing line was investigated. One bin of naturally infected ‘Scired’ fruit was harvested from an orchard with known high incidence of BER, then placed into a coolstore at 0.5±0.5°C for 1 week until treated. All fruit were passed through a high pressure water washer then air-dried. Half the bin’s fruit were packed into cardboard trays in apple boxes with a plastic polyliner. The other half were treated for 2 min with hot water at 51°C in a semi-commercial hot water bath, then air-dried before packing as before. After all treatments were conducted, fruit were placed in a coolstore at 0.5±0.5°C and assessed after 6, 12, 16 and 20 weeks. After 20 weeks of coolstorage, the hot water-treated fruit showed less lesion growth (identified by symptoms as BER) than untreated control fruit. HWT effectively reduced both lesion size and number of natural infections by Neofabraea alba by 93 and 84%, respectively, and shows promise for use in commercial packhouses.