Background: This study is meant to evaluate the variability in the germination
pattern of the coconut types and the effect of climatic factors on their
germination.
Methods: Matured seed nuts from 124 genotypes of the Green Dwarf (GD), Orange
Dwarf (OD), Yellow Dwarf (YD) and Tall (T) ecotypes were sown in the nursery
over a period of two years.
Results: Among the coconut types evaluated, YD had fastest emergence in 54.5
days while OD had the shortest duration of 32.5 days between the commencement
and completion of emergence. Days to emergence was affected by the viability
of the embryo and the climatic factors except rainfall. Humidity was the most
important climatic factor required for the growth, and emergence of coconut
embryo. It positively affected Days to Emergence (DE), Emergence Interval
(EI), Twenty-five percent emergence (TFE) and Fifty percent emergence (FE)
with high positive significant correlation unlike sunshine hours and
temperature which had negative disposition to coconut emergence. With high
sunshine hours, EI, TFE and FE increased which indicated that at high
sunshine dominated periods, number of days to emergence increased as a result
of high evapo-transpiration. Temperature had negative disposition on DE, EI,
TFE and FE. At high temperature, emergence and germination depreciated and
this translated to prolonged number of days to achieve TFE and consequently
FE.
Conclusion: The YD and OD could be utilized to produce early germinating hybrid
varieties. The seed nuts meant for sowing should be allowed to mature before
harvesting. Seed nuts should preferably be under shade to maintain humid
environment and irrigation should be provided to maintain humidity during off
rain periods of planting.
Coconut is a recalcitrant seeded crop whose
embryo is peg-like or cylindrical and is embedded beneath the germ pore (the ‘soft
eye’) of the shell and it never really stops growing (Ibrahim et al., 2022). This effectively makes
the coconut viviparous (live-bearing). The embryo loses its viability if dried
for storage (as in copra), it is therefore classified as a recalcitrant seed
(Harris, 2012). The ripe fruit bunch, after harvesting does not germinate
immediately. It has to undergo the process of curing which prepares the embryo
for germination. It however loses viability if dried which is in contrast with
the bunches of fruit retained in the crown of the palm that may in certain
circumstances germinate to produce seedlings while still on the mother palm
(Harries, 2012). Matured fruit can be harvested from the palm at 11th - 13th
month after pollination and fertilization or when the skin of the husk begins
to change colour (Odufale et al.,
2021). The pericarp or outer most part of the seed nut covering the husk is
glossy which do no not permit express entry of water into the fruit until
certain level of biodegradation. Therefore, to increase the rate of moisture
absorption into the planted seed nuts, it is preferable to remove a thin slice
of the husk or create cavity in the husk to receive moisture (Ugba and Akpan,
2003).
The embryo and emerging organs rely
completely on the liquid and solid endosperm for moisture, food and energy
prior to shoot emergence and formation of leaves (Fernanda et al., 2022). Henderson 2006 identified three types of germination
and emergence pattern in palms which are: remote tubular, remote ligular and
adjacent ligular. Coconut embryos have an adjacent ligular-type of germination,
whereby the plumule emerges from the germ pore and continues to grow until it
emerges from the mesocarp while the haustorium continues to grow and fill the
endocarp cavity before the radicle eventually protrudes from the mesocarp.
Although emergence in coconut has been defined biologically to have taken place
when the embryo is stimulated and begins to grow to form haustorium. However,
coconut growers defined germination as the emergence of the integument of the
petiole (crow beak) from the husk (Fernanda et
al., 2022). Germination in coconut is affected by the fruit and nut traits.
Fruit weight, fruit length, volume of coconut water and polyphenol contents in
the husk have positive correlation with germination rate whereas, the total
soluble solvent (TSS) of nut water, husk thickness, husk weight and shell
thickness were negatively correlated with germination (Harris 1981).
Germination and emergence of seed cannot take
place devoid of the climatic factors. Crops, being active and important member
of the ecosystem are faced with the effect of climate change just like every
other members of the ecosystem. Countries especially in the sub-Saharan Africa
and the Caribbean are mostly detrimentally affected by the reduction of crops
suitable for cultivation as well as drop in yield. To minimize the impacts of
these climate and other environmental changes, it will be crucial to breed new
varieties for improved resistance to abiotic and biotic stresses Lane and
Jarvis 2007.
MATERIALS AND METHODS
This study was conducted at the coconut
nursery of the Nigerian Institute for oil palm research (NIFOR) Benin-City.
NIFOR, is a tropical environment located on longitude 050 37’ E,
latitude 060 33’ N and altitude of 149m above sea level. One hundred
and twenty-four genotypes of the Orange Dwarf (OD), Green Dwarf (GD), Yellow
Dwarf (YD) and Tall (T) varieties were involved. The study was conducted for
two years. The seed nuts were harvested from each of the genotypes when few of
the nuts in the bunches turn brown on the tree indicating maturity of the
entire fruit bunch (Odufale et al.,
2021) and were thereafter stored in the seed store and allowed to cure (Ugba
and Akpan 2003) before being transported to the nursery for sowing. Before
sowing, there was partial removal of the face (husk) close to the point of
attachment to the palm in order to increase the absorption of water and
nutrient for the embryo’s use (Fernando, 1993). The seed nuts were sown in
regular rows on ground seed bed devoid of shade using sandy soil as substrate.
The study was conducted with rain-fed irrigation as the primary source of water
for the sown seeds. However, whenever there is no rainfall for consecutive
eight days, the sown seeds were provided with water using hose-fed irrigation.
The date of germination was noted and recoded as when the crow beak was noticed
for each of the sown seed nut and this is regarded as the emergence date.
Climatic data for the duration of the study was retrieved from the Institute’s
weather station.
Parameters Evaluated
Days
to Emergence (DE): This was the number of days it took for the first crow beak
to emerge in each set of the sown seed nuts.
Emergence
Interval (EI): was the number of days between the first emergence and the last
seed nut emergence in each of the sets of the sown seed nuts.
Days
to Twenty-Five Percent Emergence (DTFE): is the number of days it took for
twenty five percent of the sown seed nuts to emerge in each set of the sown
seed nuts and
Days
to Fifty Percent Emergence (DFE): is the number of days it took for fifty
percent of the sown seed nuts to emerge in each set of the sown seed nuts.
Percentage
Emergence (PE): The number of seed nuts that emerged in each of the sown set of
seed nuts were expressed in terms of the total number of seed nuts sown per set
and is regarded as the percentage germination (PG).
Statistical Analysis
The data was subjected to Descriptive
Statistics and correlation analysis using SPSS Statistical software.
RESULTS AND DISCUSSION
Data evaluated for the descriptive statistics
of the four coconut ecotypes (Green Dwarf (GD), Orange Dwarf (OD), Yellow Dwarf
(YD) and NIFOR Tall (T)) indicated that YD had faster speed of emergence than
the other ecotypes considered in this study accomplishing emergence at 54.5
days after sowing (Table 1). The GD, OD and T germinated at 70.0, 65.5 and 80.8
days after sowing respectively. On the other hand, the OD had the least number
of days to complete and round up emergence after sowing.It took the OD 32.5 days to complete
emergence after the first seed nut had germinated while GD, YD and T had
complete emergence after 54.3, 41.3 and 34.7 days respectively from the
emergence of the first seed nut.
Results
from this study indicated that the dwarfs irrespective of the ecotype, emerged
much quicker than the tall which can be attributed to the thinner husk and
shell of the dwarf relative to the tall types. This result corroborates the
findings of Harris (2012) and Shareefa et
al., (2014) who stated in different studies that thinner husked coconut emerged
earlier than thicker husked types. However, the tall type, even though did not
commence emergence quick enough compared with the dwarfs, had the highest
emergence percentage (82.7%) among all the ecotypes (GD – 70.3, OD – 48, YD –
63.3) considered in this study (Table 1). This as well agrees with Fernando
1993 that tall coconut have higher germination percentage than the dwarf types
and this can be partially attributed to higher water content of the tall
coconut. In the Tall, desiccation of the nut and dehydration of the embryo is
less likely to be observed because of the larger content of the liquid
endosperm (coconut water) which nourishes and hydrates the embryo thus
elongating its period of viability.
Rainfall and adjoining climatic factors are
important factors to be considered when raising seedlings from coconut seed
nuts. The embryo need moisture to grow and complete physiological maturity
which was provided by the liquid endosperm. This was evident by the fact that
rainfall does not have significant correlation with the number of days to
germination (DE; r = 0.01, p=NS) but affects the germination
interval (EI; =0.32, p<0.01) (Table
2) i.e. the number of days it takes for the set of sown seed nuts to complete
germination, DTFE and DFE which were events that occur much longer after the
liquid and solid endosperm might have been used up were affected by rainfall
and are significantly positively correlated to rainfall (r=0.27, p<0.05) and
(r=0.40, p<0.01) respectively. However, humidity seems to be the most
important climatic factor required for the growth, development and germination
of coconut seed nut embryo. Its effect was immense on the DE (r=0.33,
p<0.01), EI (r=0.44, p<0.01), DTFE (r=0.63, p<0.01) and DFE (0.70,
p<0.01) with high positively significant correlation unlike rainfall whose
effect was only felt on DTFE and DFE (Table 2). At high humidity there would
have been reduced stress on the developing embryo which enhanced rapid growth
and development of the haustorium but low humidity caused the embryo to
shrivel, dry up, or get deformed which resulted in the die back of supposed
shoot (crow beak). This finding corroborates the results of Foale and Nair,
(1993) who observed that humidity had high positive significant correlation
with germination. He further stated that in as much as the humidity is 40%, and
the embryo is viable, coconut seed nut will germinate.
It can thus be suggested that rather
than wetting once in the day in the coconut nursery especially when indoor or
covered nursery is not practiced, wetting or irrigation of the seed nuts should
be done more than once in a day in order to maintain high humidity and thus
indoor or covered nursery will be preferable to open air or outdoor coconut
nursery especially during the off rain period. The percentage of seed nut that
germinated was not affected by any of the climatic factors evaluated. It was
rather influenced by other internal factors of the seed nut, probably the
viability of the embryo at the time of planting which is in line with the
findings of Ranasinghe et. al. (2010)
who stated that meiosis is sensitive to high temperature and could affect the
growth and development of the embryo. Also, Harris (1983) stated that coconut
embryo continues to develop even after harvesting and as such, seed nuts should
be allowed time to cure before sowing. Hence it is important to always allow
seed nuts meant for propagation to mature properly before harvesting to reduce
wastage of seed nut.However, the significant
negative correlation coefficient between the PE and both of DTFE (r = -0.32,
p<0.01) and DFE (r = -0.41, 0.01) indicated that the percentage of seed nut
germination affected the number of days to achieve twenty-five percent and
fifty percent seed nut germination. i.e. if the embryo in the seed nuts are
allowed to mature properly, it will increase the PE and as well shorten the
number of days to achieve DTFE and DFE which will reduce cost of irrigation
during the off rain period and also improve the chances of embryo survival and
number of seedling that can be raised.
On the other hand, unlike humidity that
promoted and supported emergence and germination in coconut, sunshine hours and
temperature had negative disposition to coconut germination. Sunshine hours had
positive significant correlation with the DE (r = 0.41, p<o.01), DTFE (r =
0.52, p<0.01) and the DFE (r = 0.53, p<0.01). With high sunshine hours,
DE, DTFE and DFE increases which indicated that at high sunshine dominated
periods, number of days to achieve germination increases as a result of high
evapo-transpiration and reduced available moisture affects number of days to
germination spread among the sown seed nuts per lot which reflects in the DTFE
and DFE. Similarly, temperature had negative disposition on DE (r = -0.26, p<0.05),
GI (0.29, p<0.05), TFP (-0.27, p<0.05) and FP (-0.26, p<0.05). At high
temperature, days to emergence increased and this translated to prolonged
number of days to achieve DTFE and consequently DFE (Table 2).
Table 1: Mean and
Standard Error of Germination Parameters of the Ecotypes
Type
DE
EI
DTFE
DFE
PE
GD
70.0±3.9
54.3±4.9
80.1±2.9
99.5±2.9
70.3±3.4
OD
65.5±7.5
32.5±9.5
72.5±14.5
106±10
48.0±4.0
YD
54.5±5.9
41.3±8.1
77.0±4.04
91.3±4.0
63.3±10.5
T
80.8±7.9
34.7±5.2
88.7±5.4
102.2±5.2
82.7±4.9
GD
= Green Dwarf, OD = Orange Dwarf, YD = Yellow Dwarf, T = Tall, DE = Days to
Emergence, EI = Emergence interval, DTFE = Days to twenty- five Percent
Emergence, DFE = Days to fifty percent emergence, PE = Percentage emergence
Table 2: Correlation
Analysis of the Germination Parameters and Climatic factors
DE
EI
DTFE
DFE
PE
Rain
Sun
Hum
Tmp
DE
1
EI
-0.50**
1
DTFE
0.77**
-0.09
1
DFE
0.60**
0.01
0.87**
1
PE
-0.04
0.01
-0.32**
-0.41**
1
Rain
0.01
0.32**
0.27*
0.40**
-0.08
1
Sun
0.41**
0.19
0.52**
0.53**
0.04
-0.05
1
Hum
0.33**
0.44**
0.63**
0.70**
-0.02
0.66**
0.58**
1
Tmp
-0.26*
0.29*
-0.27*
-0.26*
0.19
-0.14
-0.07
0.06
1
*, **: Significant
at 0.05 and 0.01 level of probability respectively
DE
= Days to Emergence, EI = Emergence interval, DTFE = Days to twenty- five
Percent Emergence, DFE = Days to fifty percent emergence, PE = Percentage
emergence, Rain = Rainfall, Sun = Sunshine Hours, Hum = Humidity, Tmp =
Temperature
CONCLUSION
The YD which showed prospect of early
germination can be suggested to be included in early germination population improvement
collections. Also, it should be adopted as base material in producing early
germinating and early fruiting hybrid varieties. The fruit bunch meant for
sowing should be allowed to mature before harvesting. Seed nuts when sown,
should be sown preferably under shade to maintain humid environment and wetting
in the off rain period should be done in the morning and noon to maintain
humidity which is required for effective emergence and subsequently germination
of seedlings.
Conflict of Interest
There is no conflict of interest in procedure
or process during the period of this study
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Cite this
Article: Odufale, OO; Koloche, MI; Ahanon, MJ; Nwite, AP (2024). Evaluating the
Variability of Germination Pattern of Coconut Types. Greener Journal of Agricultural Sciences, 14(2): 123-127.
