- N J R Roets
- ARC-Institute for Tropical and Subtropical Crops, Private Bag Xtt208, Nelspruit 1200, South Africa
- 2003
It is known that the application of plant growth substances can effect fruit retention and fruit size, depending on the application time and the concentration used. Trials were undertaken in the Malelane and Nelspruit areas to determine the effect of the synthetic cytokinin, CPPU. and CPPU in combination with the gibberellins, ProGibb® (GA3) and Promalin® (GA4,7), on fruit size and retention of ‘HLH Mauritius’. Applications were made during early fruit development. With early treatments, two to seven days after full female bloom, fruit drop was significantly increased with CPPU and CPPU in combination with ProGibb® and Promalin®. No significant increase in fruit size was obtained. This caused a significant reduction in yield. With the later treatments, two to three weeks after full female bloom, no significant effect on fruit drop was observed. Although not significant, fruit size was slightly increased by the CPPU treatment alone. No significant increase in fruit size occurred, where CPPU was used in combination with ProGibb® and Promalin®.
Summary:
- The study investigated the effects of synthetic plant growth substances, particularly the cytokinin CPPU and gibberellins (ProGibb GA3 and Promalin GA4,7), on fruit retention and size in the litchi cultivar HLH Mauritius.
- Experiments were conducted in the Malelane and Nelspruit areas, with treatments applied at different times after full female bloom (FFB)—early (1-2 weeks) and later (2-3 weeks).
- Early applications of CPPU alone or in combination with gibberellins significantly increased fruit drop, leading to reduced yield.
- This suggests a fruit thinning effect by CPPU when applied early.
- No significant increase in fruit size was observed with early treatments, although there was a slight, non-significant increase in fruit size with CPPU alone.
- Later treatments (2-3 weeks after FFB) did not significantly influence fruit drop but showed a slight, not significant, increase in fruit size with CPPU alone, whereas combinations with gibberellins slightly decreased fruit size.
- Fruit retention and size were measured by fruit mass and percentage of fruit drop from 10 days after FFB until harvest, showing that early CPPU applications caused higher fruit drop.
- The study noted that CPPU’s fruit thinning effect is consistent with findings in other crops such as apples and muskmelons.
- It was concluded that early CPPU treatments reduce fruit retention but do not significantly increase fruit size, while later CPPU treatments may positively affect fruit size, warranting further research for optimal timing.
- The long-term effects of these growth substances on fruit size, retention, and off-year production in litchi also require further study.
- The research was supported financially by SALGA and benefited from donated fruit from Mr. Ian Johnson of Mauricedale.