| The post-harvest life of apples is directly related to the physiological age at harvest. Present criteria for determining time to harvest such as calendar date, days after full bloom, degree-day accumulation, firmness of flesh, the percentage of ground or red color of the skin, the percentage of soluble solids, starch test, pH, and acidity are often conflicting and not satisfactory for determining physiological stages (maturity and ripening) of apples. The fact that a burst of ethylene (C(,2)H(,4)) in climacteric fruits presages ripening under natural conditions makes detection of this burst of C(,2)H(,4) an excellent indicator for the meaurement of physiological maturity.;In another study, fruits from ten 8-year-old modified central leader 'Starkcrimson' trees were analyzed during 10 sequential harvests from September 26 through October 27. Approximately 50 apples were picked from selected branches on one tree at each harvest date. Before harvest, the position of each apple on each tree was identified. Internal C(,2)H(,4), internal CO(,2), firmness, soluble solids, pH, and titratable acidity for each apple were determined 12 hours after harvest. After low pressure extraction under de-gassed distilled water the internal C(,2)H(,4) concentration revealed increases over 3500-fold during ripening. Apples located next to the bud scale scars are physiologically older than other apples on the same age wood and branch analyzed at the same time, as determined by the higher internal C(,2)H(,4) concentration, except the terminal fruit on the youngest bearing wood. Twin apples picked from the same fruiting spur did not necessarily have the same physiological age; the heavier fruit was physiologically older, as determined by the internal C(,2)H(,4) concentration, than the lighter fruit.;When compared to other criteria for determining time to harvest, measurement of internal C(,2)H(,4) concentration is the best maturity index in this study. As a result, two improved sampling techniques are suggested for future apple studies. By picking apples at the basal position next to the bud scale scar, an early detectable internal C(,2)H(,4) of the fruit may give the best prediction for the proper harvest date of the analyzed trees. By picking apples in the medial position of the same age wood, more uniform fruit samples can be obtained because the within-tree variation is minimized.;Using the C(,2)H(,4) burst as an indicator of physiological maturity, a study was undertaken to determine the differences of physiological age of apples located on different portions of three 'Wellspur' trees. Each tree was separated into four portions: high outer portion, high inner portion, low outer portion, and low inner portion. Variation of accumulated C(,2)H(,4) production due to different locations of fruit on the tree was similar to that of fruits from adjacent trees and smaller than variation between harvest dates as ripening progressed. |
