Pg. 6-10 Effect of the time of bud-break in winter, as manipulated by the commencement of irrigation, on flowering intensity of ‘Mauritius’ litchi trees

In ‘Mauritius’ litchi, country yield and the tree flowering intensity are strongly correlated. General failure to flower is associated with poor years, and intense flowering, with exceptional years. Pronounced seasonal variability in cropping is recognized as a significant problem. It was observed that the time of the commencement of irrigation can markedly influence the time of bud development during the winter months in ‘Mauritius’ litchi. Timely release from a relative drought stress may therefore effect general bud-development when conditions are ideally inductive. The aim of the present study was to assess the effect of the release from drought stress on various dates during winter, after its early
imposition, on the intensity of flowering, as well as on fruit retention, in ‘Mauritius’.

Trees were pruned (30 to 40 cm heading back of all branches) on February 8, 9 and 10, 2005, at the time when general postharvest flushing was beginning. Pruning was effective in causing a uniform flush response, bud development having occurred generally by February, 2005, in the pruned trees. To determine the effect of release from drought stress after its imposition, the microsprinklers irrigating the trees were blocked on April 15, after the post-harvest flush had generally materialized. Irrigation was reinstated on a number of dates, namely, June 9 (L₂), July 4 (L₃ ), and July 15 (L₄, L₅ , L₆ ) 2005. Ethrel (150 ml Ethrel per 100 l water, dates April 15 and May 5) was sprayed on the trees in April and May, 2005, to prevent new flush from developing during these months.

Flowering intensity or percentage of inflorescences bearing fruits was not markedly affected by the treatments, flowering intensity being greatest in the untreated and trees released latest from drought stress (July 15, 2005). Drought imposition was apparently effective to an extent in delaying bud development. Trees pruned and released from drought stress on July 15, 2005, were generally as productive as, or more productive than, the untreated trees. Inflorescences developing later in the season tended to set fruits, whereas those developing earlier were prone to fruitlessness. Correlative analysis relating stage of growth and development in July or September 2005, to flowering intensity or inflorescence fruit setting ability as seen in late October 2005, confirms the supposition that the time of winter bud development as it relates to winter temperatures, directly determines whether inflorescences develop or not, as well as the ability of the inflorescences to set fruits. Future research is to be aimed at assessing the date of post-harvest pruning on flowering intensity and inflorescence fruit setting capacity in view of the effect of pruning on flushing time, and shoot maturation stage when conditions are maximally inductive for flowering.