EFFECTS OF AVG AND 2,4-DP ON PREHARVEST DROP AND FRUIT-QUALITY OF TSUGARU APPLES

The effects of aminoethoxyvinylglycine (AVG) and 2, 4-dichlorophenoxy-propionic acid (2, 4-DP) applications to apple cv. Tsugaru on 1) preharvest drop, 2) internal ethylene concentration, 3) 1-aminocyclopropane-1-carboxylic acid (ACC) content, 4) ACC oxidase activity, 5) abscisic acid (ABA) content and 6) fruit quality during storage at 1 degrees C were investigated. 1. Foliar applications of 90 or 180 ppm AVG were made on whole trees 96 or 109 days after full bloom (DAFB); a 45 ppm 2, 4-DP spray was applied 96 DAFB. Although the preharvest drop of the untreated control amounted to 32.1%, it was only 1.3% and 1.9 similar to 6.7% with 2, 4-DP and AVG applications, respectively. 2. Internal ethylene concentration and ACC content in the peel and pulp of fruits were higher with 2, 4-DP treatment, but were lower with AVG treatment compared to the untreated control. The 2, 4-DP-treated and untreated control apples had the highest internal ethylene concentration after 60 days in storage, while the ethylene concentration of AVG-treated fruits increased gradually during 120 days in storage. The ACC content in 2, 2-DP-treated and untreated control apples increased dramatically after 20 days in storage, and then sharply decreased to its initial level. On the other hand, that with AVG application, ACC level increased slightly. ACC oxidase activity with each treatment showed a continuous increase from after 20 days in storage. These results may indicate that ACC oxidase activity besides ACC content is related to the rate of ethylene production from fruits during storage at 1 degrees C. ABA content in the pulp of 2, 4-DP-treated and untreated control apples increased rapidly after 20 days in storage and then fell continuously. Thus, ABA content in the pulp did not show a pattern similar to the increase in the internal ethylene concentration but rather to that of the ACC trend. 3. Foliar applications of AVG not only reduced preharvest drop, but they also delayed the loss of chlorophyll in the peel and the softening of the fruit during storage, i.e., fruit senescence.