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2, 4-DP(20∼45ppm) and 2, 4, 5-TP(20ppm) were applied to ´Tsugaru´ apple trees 25 days before harvest in order to compare the effects of the chemicals on the preharvest drop and softening of fruits. Both chemicals reduced preharvest drop significantly, and the effects were similar between two chemicals in the given concentrations. 2, 4-DP at 40∼45ppm and 2, 4, 5-TP at 20ppm decreased fruit firmness and total acidity, but the effects were small at 20∼30ppm of 2. 4-DP. 2, 4-DP at 20ppm and 2, 4, 5-TP at 20ppm increased red coloration of fruits slightly compared with control, but it was distinct at 40∼45ppm of 2, 4-DP. Addition of Ca(OH)₂ at 0.5∼2.0% suppressed fruit softening and red coloration remarkably, but decreased the effect of 2, 4-DP at 40ppm on preharvest drop.
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