EFFECT OF TEMPERATURE ON GROWTH AND FLOWERING OF LYCHEE
SCIENTIFIC NAME: Litchi chinensis
FAMILY: Sapindaceae
This paper by C.M. Menzel and D.R. Simpson reports the effects of temperature on growth and flowering under the controlled environmental conditions of glasshouses. The cultivars chosen are: 'Tai So', 'Bengal', 'Souey Tung', 'Kwai May Pink', Kwai May Red', 'Salathiel' and 'Wai Chee'. Plants at 20/15°C and 15/10°C were harvested at completion of flower anthesis (the indices of flowering being the proportion of branches which flowered and shoot dry matter directed to the inflorescence) and these findings were related to the vigor (dry matter accumulation) of vegetative shoots at high temperatures (30-25°C and 25/20°C). Data were also collected on nutrient content of shoots.
The experiments showed that flowering of lychee is promoted after a short period (6 to 8 weeks) of low temperatures below 20°C. Flowering was greatest at 15/10°C and did not occur above 25/20°C. At 20/15°C the relative order for flowering percentages were: 'Wai Chee' > 'Salathiel' > 'Kwai May Pink' > 'Tai So' > 'Bengal' > 'Souey Tung' > 'Kwai May Red'. Flowers were absent for 'Kwai May Pink' at 20/15° - and 'Kwai May Red' at 15/10°C. Menzel et al. underscore that in subtropical Queensland there is a high correlation between flowering and fruit set providing "spring weather is sufficiently mild".
Confirming previous studies, the authors conclude that lychee trees require a period of low night temperature (below 7 to 15°C) to flower adequately, with a two-fold effect of temperature to induce both dormancy and flowering. They state that more experiments are required to determine what exactly is the minimum number of weeks and the inductive temperature necessary for flowering, but the main prerequisite is probably a combination of day and night temperatures that prevent shoot and root growth for a few weeks.
The results of the study also suggest that in "warm environments which receive heavy rain in Autumn", low-vigor cultivars were generally more reproductive than high-vigor cultivars and confirm the importance of selecting low-vigor cultivars in warmer, wetter areas.
This study also concurs with one by Nakata and Watanabe that the effect of temperature on growth and flowering does not appear to involve significant changes in water relations, inorganic nutrition, or carbohydrate status.
Also of interest, the study defines four types of successional flowers. First, a hermaphrodite with long stamens and abortive ovary (functionally male) followed by hermaphrodite with non-dehiscent anthers (functionally female); next, a hermaphrodite with short stamens and abortive ovary (functionally male); and finally, a hermaphrodite flower which did not open and contains very short stamens and abortive ovary (non-functional).
In regards to cultivars, the 'Salathiel' has the highest proportion of female flowers (37.5%) and 'Kwai May Red', the lowest (3.3%). Coincidently, in subtropical Australia, 'Salathiel' is known for having the most consistent fruit set, while the the 'Kwai May Red' is notorious for setting few fruit per panicle.
Menzel et al. noted from a previous study that applied gibberellin has been observed to inhibit flowering by counteracting the flower-inducing influence of low temperatures. Presumably, the converse would be that activities such as cincturing (girdling), root pruning and application of growth retardants would reverse the inhibitory effects of high temperatures. This suggests to the authors that the conversion of a vegetative bud to a panicle in lychee is dependent on changes in the content of endogenous growth substances. A similar conclusion has been drawn for citrus.
DATE: March 1992
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