| Abstract: | Studies of the relative magnitude of the various componentsof the water balance of developing apple fruits are described.Water entering the fruit can be used in growth, evaporationor, subsequently, a reverse flow to other tissues. Estimatesof evaporation were obtained from the weight loss by detachedfruit hanging in their natural positions in the orchard. Evaporationrates could be estimated with reasonable precision using themaximum daily vapour pressure deficit x fruit surface conductanceto water vapour. A method is described for the measurement offruit surface conductance in the laboratory or the field. Althoughthe conductance declined markedly during the season from ca.1.5 x 10–3 m s–1 in early May to less than 1.0 x10–4 m s–1 in September, the rate of water lossper fruit only declined slightly over this period. There weresignificant varietal differences in surface conductance, withBramley apples having the lowest conductances of those studied,and Egremont Russet the highest. Fruit diameter gauges wereused to provide continuous records of diurnal fluctuations insize of attached fruit. These records were used to estimatediurnal growth and shrinkage. The calculated volume shrinkageeach day averaged 31% of net growth in early August and waslargely accounted for by evaporation, with relatively littlewater flowing out of the fruit to other tissues. |
