- J. Kift, R. Wittmann, and N.J.R. Roets
- ARC-Institute for Tropical and Subtropical Crops, Private Bag X 11208, Nelspruit 1200
- 2003
Synthetic auxins are known to affect fruit drop and size, depending on the application time and concentration used. A trial was thus undertaken to evaluate the effect of different synthetic auxins and girdling on fruit size and retention of ‘HLH Mauritius’. In this cultivar a second wave of fruit drop took place 7 to 9 weeks after full female bloom (FFB). Control trees in the Malelane area abscised 41.04% of the fruit that survived the initial fruit drop period while 24 % were abscised in the Nelspruit area. In the Male lane trial this fruit drop was reduced significantly by the 100 ppm TP, 100 ppm TP plus 20 ppm TPA and 67 ppm TP plus 20 ppm TPA treatments. These treatments had 9.86, 12.10 and 12.92 % fruit drop respectively and the reduced fruit drop resulted in higher yields of 130, 121. 7 and 117 kg/tree respectively in comparison to the 97.3 kg/tree of the control. The 100 ppm TP and the 100 ppm TP plus 20 ppm TPA treatments also had bigger fruit than the control. In the Nelspruit trial the 100 ppm TP plus 20 ppm TPA and the 67 ppm TP plus 20 ppm TPA treatments reduced fruit drop and the biggest fruit were obtained by the 100 ppm TP plus 20 ppm TPA and the SO ppm Quinmerac treatments. Both of these treatments produced average fruit of 20.S g in comparison to the 19 g of the control.
Summary:
The study evaluated the effects of synthetic auxins (2,4,5-trichlorophenoxypropionic acid – TP, and 3,5,6-trichloro-2-pyridyloxyacetic acid – TPA) and girdling on fruit size and retention of the litchi cultivar HLH Mauritius.
Litchi fruit experiences two distinct waves of fruit drop: an initial drop within two weeks after full female bloom (FFB), and a second wave 7 to 9 weeks after FFB coinciding with rapid embryo growth and endosperm depletion.
The second wave of fruit drop caused 24% to 41% fruit abscission in control trees, varying by location (Malelane and Nelspruit).
Treatments with 100 ppm TP, 100 ppm TP plus 20 ppm TPA, and 67 ppm TP plus 20 ppm TPA significantly reduced fruit drop during the second wave, resulting in higher yields (up to 130 kg/tree compared to 97.3 kg/tree in controls).
In the Malelane trial, these treatments also produced larger fruit compared to controls, with girdling at the 2 g fruit stage producing the largest fruit.
The Nelspruit trial showed different results, possibly due to different orchard management; only the combined TP and TPA treatments reduced fruit drop, and the 100 ppm TP alone did not reduce drop.
Fruit size was largest under the 100 ppm TP plus 20 ppm TPA and 50 ppm Quinmerac treatments in Nelspruit.
The study confirms synthetic auxins and girdling can effectively reduce fruit drop and increase yield in HLH Mauritius litchi, although responses may vary by location and orchard practices.
The application time critical for effectiveness was when fruitlets weighed about 2 g and embryos had a heart shape.
Girdling improved fruit retention and size by modifying phytohormone movement in the plant.
The research supports previous findings that endogenous auxin (IAA) inhibits abscission, and synthetic auxins can mimic this effect to improve fruit retention.
Overall, the combined use of TP and TPA, along with girdling, shows promise for enhancing litchi fruit size and yield.