Pg. 8-11 The Application of Plant Growth Substances can Increase Litchi Fruit Size and Yield

The occurrence of a significant and heavy fruitlet drop is typical of the litchi and is one of the main reasons for poor productivity. Synthetic auxins have been used for more than 50 years to reduce fruitlet drop in many fruit crops, including citrus, apple, pear and peach. The concentration and time of application of these synthetic auxins are extremely important. In addition to reducing fruitlet drop synthetic auxins have also been used to increase citrus fruit size without reducing the fruit number. During the past five years Israeli researchers have had great success with reducing litchi fruit drop and increasing fruit size through the proper application of the auxins Tipimon^® and Maxim^®. In addition to these products good results have also been obtained with a third product, Bonus^®. Bonus^® increased litchi fruit size, yield and fruit colour. This article is a summary of available literature and also covers the initial layout for trials under South African conditions.

Summary:

• Litchi typically suffers from heavy fruitlet drop, leading to poor productivity; synthetic auxins have been used for decades to reduce fruit drop in various fruit crops.
• Israeli research over five years showed success in reducing litchi fruit drop and increasing fruit size using synthetic auxins Tipimon^® (2,4,5-trichloro-phenoxypropionic acid) and Maxim^® (3,5,6-trichloro-2-pyridyloxyacetic acid), as well as Bonus^® (Quinmerac), which also improved fruit color and yield.
• Low litchi yields worldwide are mainly due to poor flowering and heavy fruitlet abscission; under South African conditions, vegetative growth inhibition in April/May via fertilizer, water stress, and growth inhibitors enhanced flowering.
• A typical litchi inflorescence bears 100-250 female flowers, but only 5-10% develop into fruitlets due to natural abscission, mostly fertilization failure.
• Auxins play multiple roles including cell enlargement, cell division stimulation, fruit set and growth, abscission control, and development timing.
• Cytokinins and gibberellins also contribute by promoting cell division, fruit growth, and flowering.
• The timing and concentration of synthetic hormone application are critical for effectiveness.
• Applications of TP and TPA at optimal fruit weight stages significantly reduce fruit drop and increase yield in cultivars like HLH Mauritius, Floridian, and Kaimana.
• Application of TP followed by TPA one week later further boosts yield beyond solo applications.
• Bonus^® applied at 10-15 mm fruit diameter increased fruit size, yield, and color in trials conducted in Taiwan.
• Girdling, an ancient practice removing bark rings to disrupt sap flow, is used to promote flowering, fruit set, retention, size, color, sugar content, and early ripening; it is effective when performed properly without damaging the xylem.
• Field trials under South African conditions tested various plant growth substances including NAA, CPPU, Kelpak, Promalin, and girdling, with promising preliminary results showing increased fruit size and potential for yield improvements.
• The article emphasizes integrating plant growth substances with good orchard management (including water stress and fertilization) to combat fruitlet drop and enhance yield and fruit quality in litchis.