Further studies on graft-induced off-season flowering and fruiting in mango (Mangifera indica L.).
Kulkarni V. J.
Author Affiliation: Fruit Res. Sta., Sangareddy, (AP Agric. Univ.), 502 001 India.
Journal of Horticultural Science 63 : 361-367
Abstract : Defoliated shoots of the cultivars Alphonso, Dashehari, Totapari (receptors), could be induced to flower within 4 weeks during the off-season by veneer grafting them to leafy shoots of the off-season flowering cv. Royal Special (donor) during the non-flowering season. Experiments on defoliating the donor and receptor shoots revealed the crucial dual role of the leaves in flowering. In the floral cycle, leaves from the donor promoted flowering, whereas leaves on the receptors, in the vegetative phase, were inhibitory, and prevented graft-induction of the receptors. Thus, for graft induction, leafy donors and defoliation of receptors were essential. The inhibitory effect of the leaves on the receptors was localized and did not affect flowering of the donor shoots. The similarity between these findings and those reported elsewhere for various herbaceous, day-length sensitive species supported the view that flower formation is controlled in the same way in herbaceous and in woody perennial species. A minimum threshold of the floral stimulus appeared to be another requirement for an optimum flowering response. This was concluded from an experiment in which the leafy receptors were defoliated on different dates during the off-season flowering cycle. At the end of the cycle, the defoliated receptors produced small panicles, and finally only vegetative shoots, probably indicating sub-threshold levels of the stimulus. Bud activity at the apex in the receptor was also an important pre-requisite for graft-induction. Some veneer-grafted scions which remained dormant during the flowering cycle of the donor and which sprouted much later after the completion of off-season flowering, escaped the stimulus and invariably turned out to be vegetative. It is postulated that the cyclic synthesis of the floral stimulus in the leaves in an inductive cycle, and the gap between 2 such cycles, mainly decides the flowering behaviour of mango cultivars (biennial, annual and multiflowering). Two other requirements are the absence of non-induced leaves and the synchronization of meristematic activity in the bud with the inductive cycle. Juvenile shoots from 1- to 4-year-old seedlings could not be graft-induced, unlike the shoots from mature 6-year-old seedling trees. This juvenility effect continued into the 2nd year when defoliaton of the receptor shoots had no effect and failed to induce flowering.