Pg. 9-15 Flowering and fruit retention of Mauritius litchi as affected by post-harvest pruning and pre-flowering treatments to stimulate bud-development

Trees were subjected to light (30 cm) and more severe (45 cm) post-harvest heading in early March, the withdrawal of irrigation in late March followed by its reinstatement in mid-July, potassium nitrate/kelp extract spraying in early July, or soil paclobutrazol application in late March. The effects, where applicable, on shoot maturation stage on May 5, extent of bud activity on July 15, course of bud-development on October 8, advancement of inflorescence development on October 8, and fruit retention on November 31, were assessed. Terminal shoot maturation stage on May 5 was less advanced, active buds on July 15 were less prevalent, flowering intensity on October 8 was reduced, stage of inflorescence development on October 8 was less advanced, and number of fruit retained per inflorescence on November 31 was less, in the pruned as opposed to the un-pruned trees. In the un-pruned trees, the effects of the treatments on these aspects were either non-apparent or were unclear. A highly significant positive relationship was found between the percentage of terminal buds developing on a tree on July 15 and tree flowering intensity. Buds on terminal shoots having matured by May 5 were more inclined to be active on July 15 than buds on terminal shoots that were immature or were developing on May 5. Inflorescences development occurred on both terminal shoots that had matured by May 5, or were immature or developing on May 5. On November 31, the number of fruits retained per inflorescence strongly correlated with inflorescence stage of development on October 8, the more advanced inflorescences retaining more fruits. The study strongly supports the contentions that the level of bud activity when conditions are most inductive during the winter months determines the intensity of flowering, that the terminal shoots are required to be sufficiently mature during winter for the likelihood of good flowering to be maximized, and that the time of inflorescence development in spring, as influenced my shoot maturation stage when flowering commences, bears a strong bearing on the number of fruits retained by the inflorescences.

Summary:

• The study examined the effects of post-harvest pruning and pre-flowering treatments on flowering, bud development, shoot maturation, and fruit retention in Mauritius litchi trees.
• Treatments included light (30 cm) and severe (45 cm) branch heading in early March, irrigation withdrawal and reinstatement, potassium nitrate/kelp extract spray in early July, and paclobutrazol soil application in late March.
• Assessments were made on shoot maturation (early May), bud activity (mid-July), inflorescence development (early October), and fruit retention (end of November).
• Pruned trees showed less advanced shoot maturation, lower bud activity, reduced flowering intensity, and fewer fruits retained per inflorescence compared to unpruned trees.
• In unpruned trees, treatments showed little or unclear effect on these parameters.
• A strong positive correlation existed between the percentage of active terminal buds in July and flowering intensity in October.
• Buds on mature shoots in early May were more likely to become active in July and develop into inflorescences than buds on immature or developing shoots.
• Inflorescence development stage in October positively correlated with the number of fruits retained per inflorescence in November.
• Pruning generally synchronized flushing but resulted in more immature shoots and lower flowering and fruit retention.
• The timing of post-harvest flushing influences shoot maturity at the optimal flowering induction period, affecting flowering success.
• Treatments to hasten bud development in mid-winter (e.g., paclobutrazol, potassium nitrate spray, drought stress) did not consistently improve flowering.
• The study supports the idea that the winter period’s bud activity level determines flowering intensity and that mature terminal shoots during this period increase flowering likelihood.
• Deep pruning reduced flowering and fruit set, possibly due to reduced reserves or exposure to unfavorable environmental conditions causing inflorescence desiccation.
• Understanding post-harvest pruning timing and shoot maturity can help maximize Mauritius litchi flowering and yield.
• Literature cited supports findings on pruning effects, shoot maturity, and flowering regulation in litchi and related tropical fruit crops.