Seed desiccation tolerance and germination of seven important forest tree species in Ghana.
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Date
August, 2010.
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Abstract
Seed desiccation and germination studies were conducted on seven important tree
species in Ghana namely: Garcinia kola, Garcinia afzelii, Terminalia superba,
Terminalia ivorensis, Khaya anthotheca, Entandrophragma angolense and Mansonia
altissima. Seed desiccation was carried out using silica gel as well as drying under
shade and seed germination trials conducted at various moisture contents to assess the
effect of drying on seed viability. Drying was carried out on whole seeds of G. afzelii,
T superba, T. ivorensis, K. anthotheca, E. angolense and M. altissima. In the case of
G. kola whole seeds, and seed sections/fragments namely: the proximal section (PS) and
the distal sections (DS) were desiccated. Seeds of T. superba, T. ivorensis, K.
anthotheca, E. angolense and M. altissima survived desiccation to moisture contents
of approximately 4-5% with very little or no loss in viability. Seeds of G. afzelii
declined in viability as they were desiccated and viability drastically reduced below its
“critical moisture content” of 25%. Seeds and seed fragments of desiccated G. kola also
decreased in viability as they were desiccated and viability drastically reduced below
their ‘critical moisture contents’ of 30%. Germination of T. superba, T. ivorensis and
K. anthotheca were enhanced by alternating temperatures using the Grant 2-way
thermogradient plate. Seeds of K. anthotheca placed at alternating temperatures of
20/25ºC; 20/35ºC; 25/15ºC; 25/30ºC and 30/20ºC gave 100% germination. T. ivorensis
seeds set at 15/35ºC; 20/35ºC and 30/35ºC resulted in germination percentages above
73%. On the other hand seeds of T. ivorensis placed at a constant temperature of
30/30ºC gave 87% germination.
T. superba seeds incubated at alternating temperatures of 35/15ºC; 35/40ºC; 40/25ºC
and 40/30ºC gave germination percentages of 93% and beyond. Normal seedlings of
Garcinia kola could be raised from the proximal; half proximal; distal end chipped off
and proximal end chipped off sections of G. kola seed. Water sorption isotherm curves
of all the species exhibited the reversed sigmoidal shape. Electrical conductivity
measurements of leachates from Garcinia kola seeds increased as seeds were dried to
lower moisture content.
Description
A thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology (KNUST), Kumasi, in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Seed Science and Technology)