Does litchi flowering vary with cultivars: still an enigma?

Despite litchi (Litchi chinensis Sonn.) being exact in climatic requirement, 4-6 post-harvest flushes in year and recently high winter temperature hampered flowering in litchi in northern India and further advances in our understanding of the internal factors controlling flower bud initiation in litchi trees have been surprisingly limited. A number of newer molecules which have growth regulating properties in plants have been tested for promoting/inhibiting flower production in litchi in India, but their effects have been limited to certain cultivars and geographical locations with ambiguity. Moisture stress followed by low temperature or drought and branch girdling (before 90 days of bud break) is known to check vegetative growth and promote flowering in litchi trees. Such treatments also affect gas exchange capacity, carbohydrate level and chlorophyll content of leaves. The significance of this to flowering however, is presently unknown. Experimental evidence indicates that maturity of terminal shoots and accumulation of carbohydrate in the shoot apex are in some way associated with the synthesis of the floral stimulus, the absence of which can result in lack of flowering or irregular bearing especially in the ‘China’ cultivar. Paclobutrazol (PBZ) application during September has reduced gibberellin acid (GA₃) content almost by 20% with increased abscisic acid (ABA). Lower dose of PBZ (i.e., <2.0 g m^‑1 canopy diameter) retained higher indole-3-acetic acid (IAA) and the highest flowered shoots in ‘Shahi’ litchi was observed in tree with application of 2.0 g PBZ in year of low harvest. Further research is required to unravel the relationship between carbohydrate levels, shoot maturity, endogenous hormonal content (in ‘on’ and ‘off’ year) and the synthesis and nature of the floral stimulus in litchi leaves.