Effect of hot wind on annual growth of longan (Dimocarpus longan Lour.)

Longan is one of the major off-season fruit crops at the alluvial plains of the central region in Thailand. Potassium chlorate (KClO3) application makes successful flowering and off-season production of longan possible. Changes in canopy microclimate and shoot growth performance of ‘Puang Thong’ cultivar grown at Ban Phaeo district, Samut Sakhon province was investigated. The studied site was divided into two plots corresponding with the two different times of KClO3 application; early May (plot 1) and late June (plot 2). The microclimate data showed logged events of “hot wind” which had distinct characters of high air temperature and low relative humidity. Shoots of longan trees in plot 1 showed a negative effect of “hot wind” while it caused dry-off in young flowers of plot 2. Growth rate decreased in both plots. Shoot length and the number of compound leaves in plot 2 were low and it showed incomplete flushing. The percentage of flowering was low leading to fruit yield reduction. The knowledge about the relationship between environment and tree performances will be useful for development of appropriate technology to increase off-season longan production efficiency.