Floral induction (FI) in longan (Dimocarpus longan, Lour.) trees: Part I. Low temperature and potassium chlorate effects on FI and hormonal changes exerted in terminal buds and sub-apical tissue

Floral induction (FI) in longan (Dimocarpus longan, Lour.) trees was achieved in controlled greenhouse experiments by low temperature (LT) and by the application of potassium chlorate at high temperature (HT + KClO3) during two consecutive seasons. The latter treatment was successful also at temperatures above 20 °C. The present experiment was conducted to investigate possible alterations in the concentrations of plant hormones exerted by these two methods and to relate them to the floral induction process. The following hormones were examined by radioimmunoassay in the shoot apical buds (SAB), and in sub-apical bark and wood: the auxin indole-3-acetic acid (IAA); gibberellins (GAs); and the cytokinins zeatin/zeatin riboside (Z/ZR) and isopentenyl-adenine/isopentenyl-adenosine (iP/iPA).In apical buds, the LT treatments initially increased gibberellin and auxin (IAA) concentrations, which later declined significantly as compared to the non-inductive HT control treatment. Campared to the LT treatment the influence of HT + KClO3 on GA3 and IAA concentrations were less clear. On the other hand this treatment clearly increased the cytokinins Z/ZR and to some extend also the iP/iPA content in the apical bud. In both sub-apical wood and bark CKs were increased.The study found that hormonal changes induced by LT and HT + KClO3 in apical buds and in sub-apical tissue were different for GAs and IAA on the one hand and CKs on the other. It is speculated that LT and HT + KClO3 induce floral induction in longan at least partially by different hormonal reactions.