Vol. 70 No: 4

Title:
Effect of Flower and Fruit Thinning on the Maturity of ‘Cox's Orange Pippin’ Apples at Harvest

Author:
D.S. JOHNSON

pp: 541-548

Abstract:
‘Cox’ apple trees were hand thinned to one flower or fruit per cluster at 5, 27 and 39 d after full-bloom (FB) and the rate of maturation of fruit on the tree was assessed by removing apple samples at weekly intervals before, during and after the anticipated commercial harvest date, and measuring internal ethylene concentration (IEC), firmness, soluble solids (SS) and starch content (starch iodine test). Respiratory behaviour and ethylene production by fruits removed from the trees and held at 12°C was also monitored. Background colour was measured on fruit at the final sampling date. Earlier maturation of fruits from trees thinned at FB + 5 d was indicated by increased IEC and respiration rate, and a shorter delay to ethylene production. These characteristics were not affected significantly by thinning at 27d or 39 d after FB. Although rate of starch and firmness decline and increase in SS are commonly used for predicting harvest date, these criteria are unsuitable to measure the effects of thinning on fruit maturation, since fruits from thinned trees are firmer and higher in SS than those from unthinned trees. The estimated maturity advance caused by early thinning varied according to the assessment criteria used with a maximum advance of 16 d suggested by IEC. Firmness improvement by thinning was reduced progressively with harvest delay and fruit from all thinning treatments were less green and more yellow than those from unthinned trees at the final harvest.

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