Thinning Effect of Jasmonic Acid Derivative, n-Propyl Dihydrojasmonate on Japanese Pear ‘Hosui’

Abstract

The fruit thinning effect of Jasmonic acid derivative, n-propyl dihydrojasmonate (PDJ) on Japanese pear ‘Hosui’ was investigated. During the 1996 season, PDJ at 500, 1000, or 2000 ppm was applied to flower clusters at 17 or 12 days before full bloom (DBFB), at full bloom (FB), or at 7 days after full bloom (DAFB). During the 1998 season, PDJ at 500 or 750 ppm was applied to the whole tree at 18 or 14 DBFB. All PDJ treatments before full bloom induced fruit abscission and resulted in a thinning effect. The best results were obtained with 500 to 750 ppm PDJ applied at 17 or 18 DBFB. In these treatments, the proportion of clusters that had two or fewer fruits was about 64%, compared to the control which was 16%. In addition, the position of dropped fruit on the inflorescence axis in a cluster differed among treatments. In PDJ treatment, from the 1st to 3rd fruits from the base of the floral axis in the cluster tended to abscise easily. Abscission of the 1st and 2nd basal fruits was observed in about 90% of the clusters. There were no significant differences in fruit weight, flesh firmness, brix, and titratable acidity at harvest. PDJ did not inhibit pollen tube growth in the style of the pistil, but in flowers treated with PDJ there were many abnormal ovules at FB. These findings indicate that an application of PDJ at 500 or 750 ppm, 17–18 DBFB budbreak has a consistently good thinning effect. Histological examinations revealed that PDJ causes fruit thinning by preventing fertilization and/or causing seed abortion.