龍眼 (Dimocarpus longan Lour.) 調節開花之研究

Abstract

Potassium chlorate (KClO3) is important for longan off-season production in many countries but its mechanism on floral induction is still unclear. Thus, the effect of KClO3 on off-season flowering in Fenker longan was investigated in this study. Result was shown that percentage of budbreak and flowering of KClO3 treated plants in normal season of winter were less effective and inconsistent. The percentage of budbreak in KClO3 treated tree was not significant difference but KClO3 treatment delayed flowering around 9-10 days compared to untreated tree. Flowering percentage after KClO3 treatment were 60% for trees (80 g/tree) and 100% for potted plants (2 g/plant). The inconsistent flowering and late flowering were may be because of low temperature (below 20 C) which was not suitable for floral induction by KClO3 treatment. Percentage of budbreak in KClO3 treated potted plants in off-season of summer (100%) and autumn (70%) which were higher than in untreated plants (70% in summer; 6.2% in autumn). The KClO3 treatment induced off-season flowering in both season, flowering percentages in summer and autumn were 72.5 % and 68.1 % in new shoots, respectively as compared to no flowering untreated plant. In addition, it was found that girdling inhibited vegetative flush and improved percentage of leafless panicle after KClO3 treatment. Supplying 67% of water requirement (low irrigation) showed the negative effect including the reduction of budbreak percentage and tended to reduce flowering percentage after KClO3 treatment in autumn. Well water irrigation is necessary for floral induction by KClO3 treatment in autumn. Total soluble sugar in shoots of KClO3 treated plant was significantly increased on 21st day after treatment in summer and autumn, while, root viability was decreased. The high correlation coefficient was observed between total soluble sugar content in shoots during floral induction period and flowering percentage in both summer (0.91**) and autumn (0.579*). It is considered that the increase of total soluble sugar in shoots and the reduction of root viability enhance the floral induction.