| dc.description.abstract | Vernofliagalamensis (Cass.) Less. is a potential industrial oil crop whose seeds contain 35-45%
of triglyceride oil rich in vernolic acid, a naturally epoxidized fatt~ acid with low viscosity.
Naturally epoxidized, vernolic acid is a potential useful raw material for manufacturing paints
and coatings. Exploitation of V galamensis as a crop is however hampered by poor seed retention
and ill understood seed dormancy characteristics. To address the issues of seed retention, seed
maturation studies were conducted with a view to establishing morphological markers of seed
maturity that shall enable determination of the optimum seed harvesting point. Changes in seed
colour were monitored during seed development. Seeds harvested at different maturity levels
were subjected to desiccation and germination evaluationto tease the onset of germinability
dormancy and storability. In addition, changes in seed water status and seed mass during seed
development were monitored to establish the point at which seeds acquired mass maturity. It was
found that a "scorched earth" (dark brown) achene colour largely denoted a common indicator of
mass maturity to the extent that no seed lot registered any appreciable increase in dry weight
subsequent to achievement of this colour. It thus appears reasonable to recommend that
harvesting of seeds be undertaken once the achene colour turns scorched earth in order to
minimise seed losses due to natural dispersal.
In regard to dormancy, seeds harvested at the point of natural dispersal and dried to
equilibrium water content at 20°C and 18 - 20% relative humidity were subjected to a variety of
dormancy release experiments namely: soaking, de-coating, chilling, alternating temperature
after-ripening and gibberellic acid & potassium nitrate treatments, to determine the nature of
dormancy and develop appropriate germination testing protocol. The percent germination data
were arcsine transformed and subjected to analysis of variance. The results showed that seeds of
v
MASENO UNIVERSITY
S.G. S. LIBRARY
the subsp nairobiensis were more dormant than those of the subsp afro montana var. gibbosa.
Similarly, seeds harvested from Muguga (with a cooler climate) were shown to be more dormant
than those harvested from Maseno (warmer climate). The observed significant positive
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germination response due to nipping, decoating and soaking implicate the role of the seed
pericarp in regulating dormancy and/or germination. However, the observed positive response
due to 2-weeks of cold chilling at SOC, alternating temperatures, after-ripening, light exposure,
potassium nitrate and gibberellic acid (GA3) treatment, point to the nature of dormancy as being
of the non-deep physiological type. Moreover, the results of the thermo-gradient plate experiment
confirm this non-deep physiological dormancy as being of type II, according to the classification
by Baskin and Baskin.
Seed soaking for at least 24 hours seems to be the most pragmatic protocol for use by
farmers to enhance seed germination in their fields. The same procedure may also be used in
laboratory seed germination testing. Alternatively, chilling for at least two weeks at SOC can be
used to overcome seed dormancy prior to incubating at 30/2S or 2SI17°C. | en_US |
