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Research Article
ScienceAsia 29 (2003): 189-196 |doi: 10.2306/scienceasia1513-1874.2003.29.189
A More Efficient Transplanting System for
Thai Neem (Azadirachta siamensis Val.)
by Reducing Relative Humidity
Suriyan Cha-uma,b,*, Kriengkrai Mosaleeyanona, Kanyaratt Supaibulwatanab and
Chalermpol Kirdmaneea
ABSTRACT: The objective of this study was to develop an in-vitro acclimatization technique through relative
humidity reduction for direct transplanting of woody species to ex-vitro. The survival percentage, growth
efficiency and physiological characteristics of in-vitro acclimatized plantlets and ex-vitro adaptation were
then evaluated. Thai neem (Azadirachta siamensis Val.) was selected for this research as it is a species with
high potential for regenerating soils with high salt content. Twenty-eight day-old plantlets were transferred
to environmental control chambers under controlled relative humidity (RH), which are 65 5% and 955%
for low and high RH respectively, in order to acclimatize plantlets for 42 days. It was found that leaf water
content, chlorophyll content and net photosynthetic rate (NPR) of plantlets acclimatized under low RH
conditions were significantly higher than those acclimatized under high RH conditions (control). The
relationship of leaf water content and chlorophyll content with NPR directly affects growth efficiency, leaf
area and dry weight, of plantlets. After transplanting, the water relation system [water use efficiency (WUE),
stomatal conductance (G) and transpiration rate (E)] and photosynthetic system [NPR, maximum quantum
yield (Fv/Fm) and quantum efficiency of photosystem II (
 PSII)] were measured at days 0, 1, 3 and 5. The
plantlets acclimatized under low RH conditions showed higher physiological adaptation in G, NPR, Fv/Fm and
PSII, except E, than those acclimatized under high RH conditions. The plantlets acclimatized under low RH
conditions protected water loss through the leaf tissues by the function of stomata closure as indicated by low
E values. Consequently, the survival percentage of plantlets acclimatized under low RH conditions was
higher by a factor of 2.3 than those acclimatized under high RH conditions. In-vitro plantlets acclimatized by reducing RH produced vigorous plantlets and directly transplanted to ex-vitro with a high survival rate of
87.5%.
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a National Center for Genetic Engineering and Biotechnology, National Science and Technology, Development Agency, 113 Thailand Science Park, Pathumthani 12120, Thailand.
b Department of Biotechnology, Faculty of Science, Mahidol University, Bangkok 10400, Thailand.
* Corresponding author, Email: suriyanc@biotec.or.th
Received 18 Sep 2002, Accepted 26 Mar 2003
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