Pg. 26-30 Possible Pollination Factors Causing Fruit Drop in Litchi (Litchi Chinenesis Sonn)

This report supplies information about the competition between pollen tubes originating from different pollen donors and the effect it has on fertilisation. Results of fruit drop patterns between self- and open-pollinated and between self- and cross-pollinated flowers showed that two to three fruit drop waves occur in HLH Mauritius and Floridian litchi trees.

Summary:

• Litchi trees are monoecious, bearing male and female flowers in succession to promote cross-pollination but allowing some self-pollination due to overlapping flowering phases.
• Cross-pollination generally improves fruit set, yield, and quality, but monocultivar orchards capable of large yields suggest some self-compatibility.
• Fruit drop occurs in multiple waves (2-3), with patterns differing between self-pollinated and open-pollinated trees in cultivars studied (HLH Mauritius, Floridian, Bengal Madras).
• Causes of fruit drop include failure of fertilization, embryo abortion, nutritional/hormonal imbalances, and environmental factors.
• The study found competition between pollen tubes from different pollen donors on the same stigma, impacting fertilization success.
• Viability differences between pollen types (M1 and M2) affect pollen germination and tube growth, influencing fertilization and thus fruit retention.
• Fruit drop waves correspond to fertilization failure (early fruit drop) and embryo development stages (later fruit drop), especially in self-pollinated fruit due to possible inbreeding depression.
• No significant yield difference was found between self- and open-pollinated trees despite different fruit drop patterns, suggesting resource limitations in fruit retention.
• The study supports the hypothesis that fruit drop in litchi is mainly a physiological issue involving hormonal and nutritional competition among developing fruits, rather than a genetic problem.
• Further research into hormonal control and physiological processes is recommended to manage fruit growth and reduce fruit drop.
• The effects of pollen donor competition, pollen viability, and maternal resource limitations are key to understanding and potentially mitigating litchi fruit drop.
• Results were supported by detailed laboratory and field experiments in South Africa and Israel, involving hand and open pollination treatments and microscopy to track pollen tube growth.
• The study highlights the importance of pollen viability and competition for improving fruit set and yield in litchi cultivation.