APPLES AND KIWIFRUIT, CAN WE LEARN FROM EACH OTHER?

Although apples and kiwifruit are both perennial, deciduous fruit plants, they differ markedly in their growth habit and in their period of time in domestication. Nevertheless, both crops have to find a niche on the supermarket shelves, with the attendant discipline on fruit quality, both visual and internal. The current emphasis on fruit dry matter as a surrogate for taste in kiwifruit is an attempt to respond to customer preference – to fit the product to the market. The greater cultivar choice with apples inevitably provides the customer with a range of visual and taste options. In apple, the major emphasis has been on picking the fruit at the correct maturity for long-term storage and the maintenance of flesh firmness – the crisp texture of apples is a key marketing requirement. There has been far less emphasis on defining flavour and taste in apple. For kiwifruit, which are normally eaten soft, flavour becomes the dominant fruit quality attribute. Apple shares many similarities to kiwifruit in the overall pattern of starch accumulation, fruit dry matter content and fruit composition. However, both fruit dry matter content and size in apple appear to be more easily manipulated by environmental and management variation than in kiwifruit. Canopy structure, however, is very different in apple compared with kiwifruit - many apple fruit are exposed to the sunlight for long periods during the day, a necessity to develop good fruit size, colour and soluble solids; most of the fruit are borne on perennial rather than annual wood and, although there is competition between developing shoots and fruit after flowering, shoot growth normally ceases after two months compared with a fruit growth period of 4–6 months. Apple also has a higher harvest index than kiwifruit, with mature trees on dwarfing rootstocks achieving over 70% of the annual dry matter production in the harvested fruit. The high allocation of carbohydrate to the root system and the long period of vegetative growth in kiwifruit limit the possibility of increasing the harvest index. Suitable dwarfing rootstocks or major changes to the growth habit of the scion cultivar could increase both the harvest index and the fruit dry matter content.