PREHARVEST FACTORS AND POSTHARVEST QUALITY DECLINE OF APPLES

Abstract

Two types of experiment were conducted to identify preharvest factors that might be correlated with fruit quality at harvest and rate of postharvest loss of quality. The research was planned as a first step towards predicting the loss of quality in terms of firmness, green ground colour, acid- and soluble solids concentration. The first, inventory experiment involved a large number of orchards of 'Cox's Orange Pippin', 'Elstar', 'Red Boskoop' and 'Jonagold', all on M9 rootstock. Samples for chemical fruit analysis were taken 3 weeks before harvest and at harvest. Fruit for quality measurements were collected at harvest and after storage and shelf life. In the second experiment, N, P, K, Ca and Mg were applied, each at 5 levels, in a new orchard planted with 'Elstar' on M.9 to create fruit with different concentrations of these nutrients in order to study the relationship with post-harvest quality development. Fruit firmness at harvest was negatively correlated with fruit nitrogen level in August and at harvest and (in 'Elstar') with leaf nitrogen level in June and July. Green ground colour was (at least in 'Elstar') correlated positively with leaf and fruit nitrogen level in June, July and August, but not in September. Acid concentration was highly correlated with fruit K and Mg levels and with fruit weight at harvest. In 'Elstar', total soluble solids content was correlated positively with leaf P level and % of dry matter. Following storage and shelf life, the level of fruit characteristics was generally best correlated with the level at harvest. To a smaller extent significant correlation was observed with nutrients that did not correlate significantly with the level at harvest (e.g. P and Mg with firmness). The correlation between acid concentration and fruit K and Mg concentration, already high at harvest, was even higher after storage. Multiple regression models explaining the loss of firmness during storage and shelf life had a better % of variance accounted for than those explaining the absolute level at any moment. These first results are discussed in physiological terms and with respect to their possible significance for cultural practice and for prediction of fruit quality.