PHYSIOLOGY OF FLOWERING IN MANGO STUDIED BY GRAFTING

Flowering in mango appears to be regulated by floral and vegetative cycles. Off-season flowering could be readily induced in single flowering cultivars such as Alphonso and Dashehari by veneer grafting their defoliated receptor shoots onto leafy donor shoots of multi-flowering cultivars such as Royal Special. Unexpectedly and inexplicably, the response to graft induction was weak in receptors of some regular flowering cultivars such as Banganapalli.

Leaves played a crucial role in flowering. In the floral cycle, they were the sites of synthesis of the floral stimulus in the donor whereas in the vegetative receptors, they inhibited flowering as evinced by the absolute necessity of timely defoliation of leafy receptors for graft induction. Darkening the leafy receptors simulated defoliation and caused flowering in them. The newly-emerged etiolated panicles 'greened' rapidly after exposure to sunlight. Darkening the donor shoots on the other hand, prevented flowering suggesting that the flower - promotory and -inhibitory roles of leaves are mediated through some light-induced effects.

In the years subsequent to first graft induction, the receptors which had grown into branches could be graft induced by receptor defoliation to synchronise with the off-season flowering cycle of the donor, but a certain degree of shoot autonomy had established as some shoots which remained dormant during the donor's floral cycle failed to flower in spite of total defoliation of the receptor. Such shoots could however be readily induced if detached and grafted separately on the donor. Receptor branches which did not flower in the main season or those which were deblossomed/defruited at early stage of fruit growth flowered in the off-season whereas those which had carried the main season's fruit load failed to flower again in the following off-season.