REPRODUCTIVE ECOLOGY OF Saraca asoca (Roxb). De Wilde: AN IMPORTANT THREATENED MEDICINAL TREE SPECIES.
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Date
2004
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UNIVERSITY OF AGRICULTURAL SCIENCES GKVK, DHARWAD
Abstract
"Saraca asoca (Roxb). De Wilde, is an economically important medicinal
tree species that has been identified as a flagship species for conservation in
India because of its threat status. A study was carried out on two natural
populations of S. asoca of Uttara Kannada district at Banavasi and Devimane
Ghat to understand its breeding system, regeneration and to standardize a
vegetative propagation protocol to aid its genetic improvement. S. asoca
predominantly blooms during summer and has a large time window of flowering
from January to May. This andromonoecious tree bears inflorescence with equal
frequency of normal bi-sexual flowers and functionally male flowers (with
rudimentary gynoecium), shows a self-incompatibility index of 0.12 and belongs to
""mostly-incompatible"" category. For the first time we have identified floral
polymorphism for floral colour (red and yellow morphs), stigma colour (red and
yellow morphs) and floral arrangement (compact and loose). These variations
may represent a case of balanced polymorphism and are useful as markers.
The floral syndrome of S. asoca is typical of ornithophilous species-brightly
coloured flowers with sweet fragrance and copious amount of nectar but flexible
enough to accommodate opportunistic pollinators such as butterflies. S. asoca
produces large recalcitrant seeds typical to wet evergreen forest tree species vv^ith
a critical moisture content around 35 per cent. The germination of S. asoca seeds
does not require any special pre-treatment. Propagation through non-leafy stem
cuttings treated with 2000 ppm Indol Butyric .Acid (IBA) in dust form and placing
them in coir pith media resulted in higher per cent rooting among the stem cuttings
apart from increasing the number of roots as well as longer lateral roots.
The reproductive success of S. asoca is constrained by lack of effective
pollinators, narrow anther dehiscence, poor pollen grain viability period, and high
level of seed predation by mammals / insects. This has resulted in very poor
natural regeneration through seeds (with 0.08 seedlings per adult) and may lead
to genetic bottlenecking of populations."
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