Hormonal changes in response to paclobutrazol induced early flowering in mango cv. Totapuri

Abstract

Paclobutrazol has been found predominantly effective in the induction of early flowering and thus finding scope for off-season production in mango. The precise physiological mechanism regulating early floral induction is meagerly understood. The objective of the study was to examine the hormonal relationships associated with floral induction in mango following paclobutrazol treatment. The paclobutrazol applied as soil drench, @ 3.0 ml/m canopy diameter during the 3rd week of August advanced fruit harvest period by 22 days as compared to untreated trees by promoting early flowering. The C:N ratio in shoots, leaf water potential (ψw) and ABA content in the paclobutrazol untreated and treated trees increased progressively as shoots approached bud break stage. There was increase in C:N ratio and leaf ψw, by the paclobutrazol with drastic increase at the bud break. C:N ratio in shoot was positively related to ABA content in buds. Cytokinins – zeatin (Z), zeatin riboside (ZR) and dihydrozeatin riboside (DHZR) in buds increased consistently from 30 days before bud break till floral bud initiation. In paclobutrazol treated trees, increase in ZR and DHZR contents in buds were positively related to leaf ψw. GA4, GA3, GA7 and GA1 were the prominent GAs in the leaves and buds. In buds, these gibberellins followed trends opposite to that of cytokinins. The paclobutrazol treatment declined GA4, GA3, GA7 and GA1 contents both in leaves and buds; with buds being more receptive to paclobutrazol treatment. These results implicated that paclobutrazol besides affecting gibberellins also increases ABA and cytokinin contents concomitant with C:N ratio and leaf ψw in mango buds to elicit flowering responses.