- N J R Roets
- ARC-Institute for Tropical and Subtropical Crops Private Bag X11108, Nelspruit 1100, South Africa
- 2004
Flower initiation in the litchi cultivar ‘HLH Mauritius’ takes place during the drop in temperature in the beginning of winter. Trials were undertaken with different rest breaking agents in an attempt to stimulate growth when conditions were favourable for flower initiation. In Nelspruit branch treatments were made with KN03 (1%, 2% and 3%), LB urea (0.5% and 1.0%), Dormex® (0.5%, 1.0% and 2.0%), CPPU (5, 10, 20 and 40 mg/L), Kelpak® (0.4%), Promalin® (0.02%) and ProGibb® L) on their own or in combination. Treatment dates were 7 April, 21 April and 5 May 2003. Although none of the treatments improved all aspects investigated (flowering, fruit set, retention and fruit size), the 3% KNO3 0.5% LB urea and 0.4% Kelpak® treatments on 5 May showed the best results. Additionally, applications were made on trees in the Malelane area with 200 ml/tree Kelpak® and Ultra Hume® (mid March), 3% KN03 and 40 mg/L CPPU (beginning May), as well as tip pruning and tip pruning in combination with 3% KN03 (first and third week of April). Late flush was treated with 0. 05% Ethapon®. The 3% KN03 and 200 ml/tree Kelpak® gave the best results, while the tip pruning treatments gave negative results regarding flowering and production. All treatments except the 200 ml/tree Kelpak® significantly improved fruit size. These positive results are encouraging and it is important that research with rest breaking agents should continue.
Summary:
- Purpose: Investigates rest-breaking (bud-break) agents to stimulate litchi bud growth during the winter fall to improve flowering and subsequent yield in HLH Mauritius litchi trees in South Africa.
- Study sites and design: Two experiments in South Africa.
- Experiment 1: Whole-tree treatments on 12-year-old HLH Mauritius trees in Malelane area with various substances applied in March–May 2003; measured growth timing, flower vs. vegetative growth, fruit set, fruit size, yield, and climate data.
- Experiment 2: Branch treatments on 36-year-old HLH Mauritius trees in Nelspruit area with 20 branches per treatment, treated at four times (April–May 2003); assessed growth type, fruit set, fruit size, and climatic data.
- Rest-breaking agents tested: KN03 (potassium nitrate), LB urea, Dormex (hydrogen cyanamide), CPPU, Kelpak (seaweed extract), Promalin (GA4,7), and ProGibb (GA). Some combinations were explored.
- Key findings (Malelane, Experiment 1):
- Some treatments altered reaction time (time to first growth) relative to controls; mid-March applications of Ultra Hume affected reaction time; tip pruning generally delayed bud break.
- Dormancy levels (buds that did not start growth by Aug 31) were mostly unaffected, though pruning increased dormancy in some cases.
- Flowering was reduced by some pruning treatments, while several chemical treatments did not significantly differ from control in flowering.
- Fruit set: Tip-prune treatments often reduced fruit set; smaller panicles correlated with fewer fruits per panicle in some pruning scenarios. Ethapon® at 0.05% sometimes reduced fruit number per panicle, possibly due to abscission.
- Fruit retention: Generally not improved, except Ethapon® 0.05% which reduced fruit drop to 58%.
- Fruit size: Most treatments improved fruit size, with notable improvement using 3% KN03 and 200 mL/tree Kelpak®, and tip-prune + 3% KN03 combinations. Larger fruit tended to coincide with lower fruit per panicle.
- Yield: Overall yields were lower than control, except for 3% KN03 and 200 mL/tree Kelpak® which exceeded 10 t/ha, and a promising 9.5 t/ha from tip-prune + 3% KN03.
- Key findings (Nelspruit, Experiment 2):
- Reaction time: No significant change for 7 Apr applications; later applications (21 Apr and 5 May) showed some delays with higher Dormex concentrations due to phytotoxicity. CPPU caused 1–2 week delays, especially with combinations with ProGibb.
- Bud dormancy: No significant differences across treatments.
- Flowering: Most CPPU treatments improved flowering; 0.4% Kelpak® on 5 May also improved flowering. Dormex at higher concentrations near flowering time tended to reduce flowering due to phytotoxicity.
- Fruit set and fruit retention: CPPU generally reduced fruit set; some KN03 and Kelpak treatments improved flowering and/or retained fruit better when applied near normal flowering time. CPPU treatments tended to have higher fruit drop.
- Fruit size and yield: Mixed results; some KN03 and Kelpak treatments improved fruit size, and certain combinations yielded larger fruits, but CPPU did not consistently improve fruit size and sometimes reduced mass. Overall, no uniform improvement across treatments.
- Notable conclusions:
- Rest-breaking agents can influence flowering and fruiting in litchi, but timing and concentration are critical. End-of-April applications of 1% KN03, 3% KN03, 0.5% LB urea, and 0.4% Kelpak showed potential for improving flowering and related traits. Tip pruning generally had negative or mixed effects on flowering and production.
- Dormex and various growth regulators did not yield consistent benefits and may show phytotoxic effects at higher concentrations or inappropriate timing. Kelpak soil applications showed promise and warrant further investigation in combination with other products. The authors stopped short of broad recommendations, noting results are preliminary.