Effects of Retain™ on fruit maturity and fruit set of pear cultivars Williams and Packham's Triumph

Abstract

ReTain™ (Aminoethoxyvinylglycine: AVG), a newly registered commercial product, is an ethylene biosynthesis inhibitor that delayed fruit maturation if applied before harvest and increased fruit set if applied after bloom in pears and apples. The present study was conducted to observe the effects of a preharvest application of ReTain™ on the maturity of pear cultivars Williams and to determine the effect of a spring application on fruit set of Packham's Triumph . Two weeks before harvest trees of Williams were sprayed in a complete randomized design with the following treatments: 1. AVG 180 mg/L + surfactant SilWet 100ml/100l; 2. AVG 125 mg/l + surfactant SilWet 100ml/100l; 3. AVG 125 mg/L + surfactant SilWet 50ml/100L; and 4. Unsprayed control. Preharvest fruit drop, internal ethylene concentration and other fruit maturity indices (weight, flesh firmness, starch index, soluble solids and titratable acidity) were evaluated at early harvest and at 3 more times every 7 days. ReTain™ did not control preharvest fruit drop. Treatments 1 and 2 reduced significantly fruit internal ethylene concentration. There was no difference in fruit maturity after keeping the fruits 100 days in cold storage at 0 °C. Trees of Packham's Triumph were sprayed with ReTain two weeks after full bloom at two concentrations: 200 and 400 mg/L a.i., both with a surfactant SilWet 100ml/100L and an unsprayed control. Evaluations were made for fruit set after June drop, number of fruits per limb cross sectional area, fruit size at harvest, fruit seed content and percentage of deformed fruits. Fruit set was increased on treated trees. The higher concentration gave the highest fruit set and number of fruits per limb cross sectional area. Smallest fruit diameters were found in treated fruits. Lateral and terminal shoot growth was reduced significantly by the treatments and this was more marked at 400 mg/L.