Open access publications in the SLU publication database

Abstract

To increase apple production in Sweden and to improve apple quality and competitive edge on the market, solutions to negative problems such as bruising susceptibility, decay and weak storage potential have to be discovered. This thesis investigated problems relating to apple quality and storability, based on the results of field and laboratory experiments conducted in Kivik, Sweden, during a period of 12 years. Four cultivars (Aroma, Ingrid Marie, Cox’s Orange Pippin, and Katja) were predominantly used for the investigations. The cultivar Aroma showed the highest internal phenol content and was the most sensitive to bruising, followed by cv. Ingrid Marie. Enhancement of water loss and melting of skin wax by air pre-cooling or post-harvest heating decreased the incidence of bruising. A significant negative correlation between skin colour and bruise susceptibility was found in some cultivars. Decay caused by Pezicula malicorticis was the most difficult problem during storage, followed by decay due to Colletotrichum gloeosporioides and Penicillium expansum. Cvs. Aroma and Ingrid Marie were more susceptible to decay than Cox’s Orange Pippin and Katja. Post-harvest heating alone or in combination with ULO storage were possible alternatives to fungicides against these pathogens. Estimation of optimum nitrogen fertigation according to soil available nitrogen and fruit development phase not only increased tree yield but also improved fruit resistance to bruising and pathogens. Excess potassium increased yield and colouration, but declined fruit quality and storability. Aluminium foil or bark mulching improved fruit quality and increased storage potential. Apples from trees pruned in July or August showed a higher resistance to bruising and disorders and also better quality than apples from winter-pruned trees. Mulching and pruning solved the colouration problems present in cv. Aroma apples. Individual and twofold management models were not sufficient to improve the productivity of cv. Katja apples, whereas multi-practice management models improved yield, fruit quality and storability. The most positive effect was the reduction in quality decline during storage. The optimum harvest date was determined as the time when several fruit quality parameters changed similarly at a slow rate. ULO-stored apples (2% CO2 and 2% O2) showed less bruise sensitivity and decay, and also better quality than NA-stored apples. Fruit from young trees were less resistant to pathogens, had higher bruise sensitivity, showed better colouration and had a shorter storage life compared to fruit from older trees.