- P J Robbertse1, J Fivaz2 and CM Menzel3
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1Department of Crop Production and Soil Science, University of Pretoria, Pretoria 0002, South Africa
2lnstitute for Tropical and Subtropical Crops, Private Bag X11208, Nelspruit 1200, South Africa
3Maroochy Horticultural Research Station, Queensland Department of Primary Industries,
PO Box 5083, Sunshine Coast Mail Centre, Nambour, Queensland, Australia 4560 - 1995
The litchi tree has a rhythmic, modular growth pattern with terminal inflorescences. The inflorescence is a heterocladic pleiothyrsoid where the dichasia are the flower bearing units. Male and female flowers are borne on variable positions on the dichasia. The relation between the position and gender of the flowers on the dichasia is discussed.
Summary:
- The litchi tree exhibits rhythmic, modular growth with terminal inflorescences described as heterocladic pleiothyrsoids, where dichasia are the flower-bearing units.
- Male and female flowers are borne in variable positions on the dichasia, with a discussed relationship between flower position and gender.
- Traditional inflorescence terminology has been confusing; the litchi inflorescence is often called a panicle but is more accurately described as a pleiothyrsoid, a determinate compound thyrse.
- The inflorescence structure includes a main axis with primary flowers, lateral branches (paracladia), and dichasia as basic flower units, all subtended by minute bracteate prophylls.
- Flower sex and position on the dichasium vary: typically, the first flowers to open (position 1) are male (M1), followed by female flowers (position 2), then male flowers (M2) in position 3; position 4 flowers often remain undeveloped.
- Variation exists where female flowers occur in position 1 or 2, especially in late cultivars and young trees, affecting the sex ratio of flowers on the inflorescence.
- Flowering phases and sex expression influence fruit set, with more viable pollen from second male flowers (M2), suggesting potential horticultural manipulation for better fruit production.
- The study highlights the importance of understanding the spatial relation of flower sex on the inflorescence for improving litchi flowering and fruit set.
- Observations were made on various litchi cultivars in different environments, noting phenological patterns and inflorescence architecture.
- Practical implications include pruning techniques to manipulate flushes and improve flowering density and timing.