T. Jaroenkit, S. Ussahatanonta, S. Thamjumrat, C. Sritontip
The determination of longan (Dimocarpus longan Lour. ‘Daw’) baseline temperature in Thailand was investigated. Sixteen newly pruned one-year-old longan trees grown in black polyethylene bags were used in this study. Eight were transferred to a growth chamber initially set at 22°C. The temperature was then progressively reduced by 2°C weekly to a minimum of 8°C. Data collected included rate of leaf flushing, chlorophyll efficiency and photosynthetic rate. The data from the chamber grown trees were then compared with those grown at ambient temperature (23-32°C).
The results showed that leaf flushing of both ambient and chamber grown trees occurred in the third week after pruning. Leaf growth, as determined by leaf size, was not significantly smaller at the lower (in the growth chamber) than at the higher (ambient) temperature. Chlorophyll efficiency as determined by Fv/Fm decreased with temperature and became highly variable at temperatures below 16°C. Photosynthetic rate of longan trees grown at ambient temperature was relatively steady at about 4.72 µmol m-2 s-1. However, the rate decreased significantly with decreasing temperature. The effect of temperature (X) on photosynthetic rate (Y) was well expressed as Y=0.651(X)-7.006 with R2=0.90. From the model, baseline temperature for longan (‘Daw’) grown in Thailand was found to be 10.8°C when the photosynthetic rate reached zero.
Jaroenkit, T., Ussahatanonta, S., Thamjumrat, S. and Sritontip, C. (2014). DETERMINATION OF LONGAN (DIMOCARPUS LONGAN 'DAW') BASELINE TEMPERATURE IN THAILAND. Acta Hortic. 1029, 163-168
DOI: 10.17660/ActaHortic.2014.1029.18
baseline temperature, heat sum, harvesting index

Acta Horticulturae