Introduction
Mango is a commercially important fruit crop of India with a
production of 12.54 million tonnes from 2.02 million hectares of
cultivation area. It exhibits wide variations in flowering and fruiting
habits due to varietal differences and diversity in agro-climatic conditions. However, availability of most of the commercial important
mango varieties in markets is restricted to April–June due to short
crop period and strong dependency of flowering on environment.
The short period during good yielding years considerably impacts
mango profitability due to price drop. One strategy to deal such
problems that showed some success in Philippines and Thailand is chemical manipulation of reproductive development for achieving
off-season mango production.
Mango induces flowering under tropical conditions during the
month of October–December due to its strong dependency on cool
winter temperature and the age of the flowering shoots. The physiological mechanism underlying mango flowering
suggested occurrence of constantly synthesizing florigenic promoter in leaves that moves to buds via phloem along with sugars,
during cold floral inductive conditions to facilitate floral induction
in growing shoots. Kulkarni suggested that the florigenic
promoter of mango is graft transmissible across the cultivars. Thus
success in chemical manipulations of flowering lies in altering the
effects of environmental conditions, particularly of low temperature required for flowering inductions.
Plant growth retardants induced manipulation in physiological
activity has been considered important determinant of productivity
enhancement in a number of fruit crops. Among the chemicals suggested, paclobutrazol is considered as one of important
plant growth retardant which restricts vegetative growth and
induce flowering in many fruit species including mango. Many investigators have reported beneficial effects of paclobutrazol in induction flowering in different mango cultivars. Inhibition in gibberellin activity following a check in the conversion of ent-kaurene to
ent-kauronoic
acid in the gibberellin biosynthetic pathway has been attributed as
the possible primary mechanism by which paclobutrazol restricts
the vegetative growth and promotes flowering. Considering that
plant growth and development are not only regulated by the cellu-
lar levels of one particular phytohormone, and mutual interactions
among phytohormones are well documented, the floral promotory
responses of paclobutrazol could also be dependent by its effects
on hormones other than gibberellins. There are enough evidences
to show that the isoprenoid pathway associated with gibberellin
biosynthesis also regulates partially the biosynthesis of other vital
phytohormones such as abscisic acid (ABA) and cytokinins. In the present investigation, we studied the
effects of paclobutrazol on C:N ratio, leaf water potential,ABA,
cytokinins and gibberellins at different durations of shoot growth
during inductive periods with an objective to elucidate their role
on mango flowering.