Maturity stages, variation within bunch and dormancy breaking treatments in relation to germination of oil palm (Elaeis guineensis Jacq.) D × P seeds
Oil palm is mainly propagated through dura × pisifera hybrid (D × P) seeds. In natural environment, oil palm seeds require more than eight months of storage to achieve 25% germination due to seed dormancy. Currently, commercial seed producers adopt heat treatment to alleviate dormancy in D × P...
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Format: | Thesis |
Language: | English |
Published: |
2020
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Subjects: | |
Online Access: | http://psasir.upm.edu.my/id/eprint/99376/1/FP%202021%2013%20IR.pdf |
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Summary: | Oil palm is mainly propagated through dura × pisifera hybrid (D × P) seeds. In
natural environment, oil palm seeds require more than eight months of storage
to achieve 25% germination due to seed dormancy. Currently, commercial seed
producers adopt heat treatment to alleviate dormancy in D × P seeds with
monthly germination ranging from 62.2% to 72.0% within four months after
being harvested. Since the demand for oil palm is increasing, there is a need to
increase the supply of pre-germinated D × P seeds. Therefore, improvement in
percentage of germination, uniformity, and reduction in time to germination
will benefit the industry tremendously. This thesis focuses on both the pre- and
post-harvest factors in improving the germination of oil palm D × P seeds. In the
first experiment, the effect of harvesting at three maturity stages (18, 20 and 22
weeks after pollination or WAP) and six seed positions within a bunch
(Proximal-Base, Proximal-Apex, Middle-Base, Middle-Apex, Distal-Apex and
Distal-Base) on seed qualities were evaluated in a split-plot design. Seeds
harvested at 20 WAP had 80% black coloured seeds, 19% moisture content with
highest germination of 85.1%, compared with 70.5% and 80.9% for 18 and 22
WAP, respectively. Increasing seed maturity from 18 to 20 WAP showed more
seeds shifting from semi-white and white to black (up to 40% more). Seeds
located at the base region of the spikelets were smaller in size and were
predominantly white with no differences in germination capacity. In the second
experiment, the morphological and physiological performance of oil palm D × P
seeds varying in colour were evaluated. Four replicates of 10 and 100 seeds, laid
out in Completely Randomised Design (CRD) were used for seed
characterisation and germination test, respectively. Thirty pre-germinated D × P
seeds from each replicate were then transferred to the nursery for morphological, physiological and growth assessment. Germination test showed
that all the seed types indicated similar germination percentage (more than 78%)
and speed (13- 15 days of mean germination time). The nursery assessment
showed that seedlings from the black seeds have higher growth (biomass, total
leaf area, stem diameter) for the first 3 months due to the relatively larger size of
the seed. No differences in growth were observed from 6 until 12 months after
sowing. Physiological evaluation including net photosynthesis (5.30 to 18.13
µmol CO2 m-2 s
-1
), chlorophyll contents (5.70 to 9.68 mg cm-2
), stomatal
conductance, transpiration rate as well as the intercellular CO2 concentration
showed different seed colour produces physiologically similar normal
seedlings. The third experiment was designed to elucidate the effect of eight
dormancy breaking methods (operculum removal, 60 days storage, 60 days heat
treatment, 120 days storage, 60 days storage + heat treatment, 180 days storage,
120 days storage + heat treatment and control) on seed germination based on
physical, morphological, and physiological dormancy characteristics. The
imbibition test indicated that less than 7% mass increment was recorded in all
treatments after 240 hours of imbibition, while the embryo showed 10 to 20%
increase in moisture after imbibition. Final germination of more than 82% was
obtained for heat treated seeds, and seeds stored prior to heat treatments, along
with less than 13 days of mean germination time. Morphological dormancy
evaluation indicated that the embryo was fully developed at 20 WAP, but
application of heat treatment was able to accelerate the growth after being
imbibed. The physiological dormancy aspect was found to be associated with
reduction in peroxidase (POD) and catalase (CAT) activities, along with increase
in α-amylase production in the endosperm and embryo tissues. The heat and
storage treatments cause up to 36 % reduction in POD and 13% in CAT activity
levels, with 9% (endosperm) and 26% (embryo) increment of α-amylase. Based
on these results, it can be suggested that oil palm seeds exhibit non-deep
physiological dormancy (PD), with heat treatment of 40 °C as the most effective
and practical dormancy-breaking method for commercial seed production. In
the fourth experiment, the efficacy of fluctuating temperature in comparison to
constant 30 °C condition on oil palm D × P seed germination was assessed. D ×
P seed samples from similar sources were placed in two locations (Banting and
Renggam), as a nested design. Oil palm seeds recorded higher germination
percentages and speed at fluctuating temperature (70 to 85%) in comparison
with the constant 30 °C (55 to 65%). Results indicated that higher temperature
amplitude at Renggam showed 15% higher germination than at Banting. In
addition, it was found that higher α-amylase activity (209.0 to 223.7 units/ ul)
was observed for seed that was germinated under fluctuating temperature
condition. From this study, harvesting oil palm D × P fruit bunch at 20 WAP,
and application of heat-treatment (40 ±2 °C) prior to germination at ambient
fluctuating temperature condition are recommended to obtain 85% final
germination within 17 days. |
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