Exploring X-ray treatments for disinfesting apples

Access for fruit to international markets is becoming increasingly challenging. The New Zealand pipfruit export industry relies on effective and accepted methods of disinfestation to maintain market access. High pressure washing during packing removes many surface pests, and development of rotary washers has significantly improved removal of more challenging pests. However, having additional treatments available would be beneficial, particularly for difficult to control pests such as apple leaf curling midge (ALCM) and internal codling moth (CM). X-ray generating technologies are currently recognized as disinfestation treatments, with accepted standards outlined by the International Plant Protection Convention (IPPC). We examined the response of four New Zealand-grown cultivars (‘Royal Gala’, ‘Fuji’, ‘Scired’ and ‘Scifresh’) to a wide range of X-ray treatments (150-1400 Gy) at a commercial Hawaiian X-ray unit. Fruit were stored for a further eight weeks, and fruit quality examined. The only cultivar that showed significant damage was ‘Royal Gala’, which exhibited internal browning symptoms. While some characteristics such as fruit firmness and particularly acidity showed some reduction, these effects were generally at high doses (>≈800 Gy). Overall, fruit appear to be tolerant to doses that will control CM, although the effect of storage time before treatment requires further examination.