6-Benzylamino purine (BA) の散布がウンシュウミカン (<i>Citrus unshiu</i> Marc.) のえき芽に及ぼす発芽促進効果

Abstract

Effects of foliar spray of 6-Benzylamino purine (BA) on the acceleration of axillary bud sprouting in satsuma (Citrus unshiu Marc. ) trees were examined to establish feasible citrus production systems necessary for year-round fruit shipment. The results obtained are as follows:1. Meteorological conditions, i.e., duration and intensity of illumination, ambient temperature and relative humidity of the air, were regulated within the regimes favorable to shoot growth in phytotrons. Under such conditions, two successive applications of aqueous BA solutions (pH 6.8) to satsuma trees at concentrations of 100 and 200ppm at an interval of four days resulted in consistent acceleration of axillary bud sprouting.2. The lower the ambient temperature, the greater the time lag in axillary bud sprouting, and also the slower the elongation of sprouted shoots.3. The effect of BA on the axillary bud burst was greater when applied during naturally quiescent periods than when applied during growth flushes. It was also greater in spring than in summer. In particular, sprouting percent of BA-treated buds was about six times that of untreated buds when BA was applied at a scheduled time of heating in plastic greenhouses for early fruit shipment.4. BA application did not induce sprouting of immature axillary buds located at basal node positions of the shoot.5. When axillary buds sprouted luxuriantly on each shoot of the tree, some of them abscised. This may be caused by severe competition for nutrient between laterals. The abscission of such devitalized shoots implies the importance of suitable distribution of nutritive substances in a tree.