Measurement and prediction of harvest maturity of Jonathan apples for storage

Abstract

Methods have been developed to measure the latest maturity at which Jonathan apples can be harvested for long term cold storage without unacceptable losses from disorders and softening. Maturity at harvest was measured by ethylene production rate, loss of green ground colour of the skin, and flesh firmness. The levels of these maturity measures were related by regression analysis to the levels of breakdown, brownheart (flesh browning) and softening which developed after storage. From these relationships, values of ethylene production, ground colour, and firmness, which measured the latest safe harvest maturity for storage without unacceptable losses, were calculated. Such values were determined for storage for seven months in controlled atmosphere and 3.5 months in air, for several orchards and for apples of different sizes. In addition, we determined methods to predict when the latest safe harvest maturity would occur. The time from the date of first appearance of the stem cavity (T-stage) was the most accurate index from which to predict the time of last safe harvest maturity. These times were 98- 119 d, depending on crop load, storage treatment, season and orchard. The date on which ripening started, as measured by increase in ethylene production rate, or loss of green ground colour of skin, could also be used to predict harvest. However, these latter changes often occurred too close to harvest date to be practically useful for prediction.