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Tropentag, October 7 - 9, 2008 in Hohenheim

"Competition for Resources in a Changing World:
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Effects of KClO3 and Water Deficit on Flowering and Growth Characteristics of Longan

Chiti Sritontip1,2, Patumporn Tiyayon2, Pittaya Sruamsiri3, Daruni Naphrom3, Pawin Manochai4, Martin Hegele2, Jens W√ľnsche2

1Rajamagala University of Technology, Lampang Agricultural Research and Training Center, Thailand
2University of Hohenheim, Institute of Special Crop Cultivation and Crop Physiology, Germany
3Chiang Mai University, Department of Horticulture, Thailand
4Mae Jo University, Department of Horticulture, Thailand


Longan (Dimocapus longan) is one of the most important subtropical fruit crops in Thailand, both in terms of crop yield and export volume. In 1998, Thai longan farmers began to apply potassium chlorate (KClO3) for inducing off-season flowering and soil drench is most effective method. Nowadays fresh longan fruits are available in domestic markets almost all year round. However, irrigation management is critical for off-season longan production that falls into the rainy season. Due to high relative humidity, high soil moisture and also low light intensity the percentage of flowering is greatly reduced when compared to on(dry)-season production.
The objective of this study was (1) to study the time-dependent hormonal changes in various plant tissues following the application of KClO3 and (2) to determine whether total carbohydrates may be limited under "off-season" fruit production system and by establishing three crops in two years. The experiment was carried out at the Lampang Agricultural Research and Training Center, northern Thailand, and consisted of 64 two-year-old longan trees (cv. Daw) randomly assigned to four treatments; well-watered ±KClO3 and water deficit ±KClO3. All trees were grown in lysimeter containers with a capacity of 150 L and treated with KClO3 in November 2007.
It was found that in water deficit and full irrigation treatments approximately 90% of all buds flowered at 25-27 days after the application with KClO3, whereas both treatments without KClO3 application did not flower. The efficiency of photosystem (Fv/Fm), leaf net CO2 assimilation rate, transpiration rate and stomata conductance were reduced in all treatments except when full irrigation was applied. Leaf chlorophyll content was not significantly different between the treatments.
The change of plant bioregulators such as indole-3-acetic acid (IAA), gibberellins (GA1,3,20 measured as GA3 equivalents), and the cytokinins isopentenyladenin/isopentenyladenosin (iP/[9R]iP) and trans-zeatin/t-zeatin riboside (Z/[9R]Z) were determined in leaves, bark, wood and terminal bud and results will be presented at the Conference. Treatment effects on carbohydrate concentration, dry matter production, fruit yield and quality in longan will be determined destructively at harvest in June 2008.

Keywords: Carbohydrate, Dimocapus longan L., leaf photosynthesis, Thailand, longan

Contact Address: Chiti Sritontip, Rajamagala University of Technology, Lampang Agricultural Research and Training Center, P.O. 89, 52000 Muang Lampang, Thailand, e-mail: chiti_s@hotmail.com

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