A study of the floral phenology of cocoa trees was carried out between 2006 and 2008 at Kubease in the Ashanti Region of Ghana, using one hundred cocoa trees from ten farm plots. The objective was to assess the contribution of floral phenology to the productivity of cocoa. Cocoa like all tropical tree species exhibited seasonally-related phenological patterns involving overlapping cycles under both intrinsic and extrinsic controls. However, unlike most tropical plants, flowering was in the rainy season. The production of new pods or cherelles increased during the major rainy season (June, July, and August), but was evenly distributed from the minor to the dry season. Production of small and medium pods peaked in August whereas production of large pods peaked in October. There was a positive correlation between new pod production and pods abortion (
Cocoa (
The study location called Kubease in the Ejisu-Juabeng District of the Ashanti Region of Ghana (Figure
Map of the study Area in the Ejisu-Juabeng District of the Ashanti Region of Ghana.
The climate is marked by high incidence of solar radiation and relatively little variation in day length.
Ten farmer-managed cocoa farms were used in the study. In each farm, ten adult cocoa trees within a 400 m2 dimension were randomly selected and tagged using red ribbon. The total number of adult cocoa trees used for the study therefore was one hundred.
For three consecutive flowering years (2006, 2007, and 2008) monthly examination was made on each tree for counts of flowers, buds, and fruit-set to determine their seasonality. The times of incidence of flower bud, flower opening, and fruit abortion were recorded as determinants of the final yield. Fifty cocoa trees on five study farms were studied each day, as this was the maximum number of trees that could be examined accurately within a single day for the relevant phenological data. For effective flower census on trees with height ranging from 5.42–11.52 m, the protocol developed by the Cocoa Research Institute of Ghana for such tall trees was adopted [
Data on temperature and relative humidity were measured by means of Data logger three times per habitat unit. The light intensity per study site was measured with Digital light meter (Extech model 401025) 0–2000 Foot Candle (Fc) range, under standardized conditions (i.e., on the ground and on sunny days, local time 09.00 am). The percent canopy cover of cocoa tree stands was estimated using a Spherical Densiometer (R.E. Lemmon Forest Densiometers, USA). Rainfall data, were taken from the meteorological station of the Forestry Research Institute of Ghana, Kumasi.
The count of flowers and other parameters taken were pooled together for all the ten farms. The flower count data were square-root
The overall phenological pattern of flowering of cocoa consisted of segmental flowering in repeated phases. Floral productions generally increased in the major rainy season which began in the month of April and peaked in July (Figure
Phenological patterns of flower and fruit production in relation to rainfall pattern at Kubease in the Ejisu-Juabeng District.
Flowering appeared to have been affected by the level of fruiting in the preceding year. About 40% of trees produced more fruits in the year 2006, leading to a good harvest by some farmers. In such situations there was late flowering of the trees in the ensuing year 2007 in spite of the onset of rains. Trees which had little fruiting in the previous year experienced early flowering. On the whole, the month with the most rain, was also the most productive month (Figure
Phenological patterns of mature flower buds, open flowers, new pods, and percentage fruit-set of cocoa trees (
Census | Mature floral buds | Open flowers | New pods | Estimated | |||
---|---|---|---|---|---|---|---|
Month | Total | Mean ± SE | Total | Mean ± SE | Total | Mean ± SE | fruit-set% |
April | 2573 | 131.15 ± 15.61 | 1511 | 75.61 ± 8.73 | 102 | 5.12 ± 0.71 | 2.4 |
May | 3289 | 186.4 ± 7.55 | 1307 | 65.35 ± 7.11 | 194 | 9.73 ± 1.12 | 3.7 |
June | 3313 | 165.65 ± 5.45 | 1480 | 74.21 ± 9.32 | 532 | 26.61 ± 3.14 | 10.1 |
July | 7246 | 362.30 ± 8.16 | 3818 | 190.70 ± 10.58 | 2061 | 103.05 ± 13.8 | 15.7 |
August | 2955 | 147.75 ± 6.08 | 2018 | 100.90 ± 8.60 | 1982 | 104.11 ± 11.61 | 28.5 |
September | 157 | 7.85 ± 3.26 | 94 | 4.70 ± 1.08 | 317 | 17.05 ± 2.37 | 173.6 |
October | 89 | 4.45 ± 0.51 | 51 | 2.55 ± 0.38 | 252 | 13.40 ± 2.37 | 64.3 |
November | 34 | 1.77 ± 0.16 | 40 | 2.01 ± 0.99 | 206 | 10.31 ± 3.06 | 55.8 |
December | 82 | 4.25 ± 0.11 | 44 | 2.24 ± 0.19 | 322 | 16.15 ± 3.80 | 71.9 |
There were many fluctuations in the floral abundance with peaks and declines in flower production. The production of new pods or cherelles increased during the major rainy season (June, July, and August), but was evenly distributed from the minor season through to the dry season (Figure
There was considerable tree-to-tree differences in the production of mature floral buds and open flowers (Table
There was highly significant (
Flower and fruit production and pod losses averaged over ten cocoa farms at Kubease, Ejisu-Juabeng, Ghana.
Months | Census | |||||||
---|---|---|---|---|---|---|---|---|
Mature flower bud | Open flower | New pods | Small pods | Medium pods | Large pods | Diseased pods | Aborted pods | |
April | 1.6 | 0.7 | 0.5 | 0.8 | 0.3 | 0.3 | 0.4 | 1.1 |
May | 3.3 | 1.7 | 0.7 | 0.6 | 0.4 | 0.3 | 0.5 | 1.2 |
June | 4.3 | 2.5 | 1.1 | 0.8 | 0.4 | 0.3 | 0.5 | 1.4 |
July | 3.6 | 2.5 | 2.9 | 1.2 | 1.1 | 0.6 | 2.0 | 3.6 |
August | 2.1 | 1.6 | 2.6 | 1.8 | 1.3 | 0.6 | 2.6 | 3.9 |
September | 0.7 | 0.3 | 0.8 | 1.5 | 1.2 | 0.6 | 2.7 | 3.8 |
October | 0.8 | 0.4 | 1.1 | 1.6 | 1.1 | 0.6 | 2.6 | 3.8 |
November | 0.8 | 0.4 | 0.8 | 1.3 | 0.8 | 0.5 | 1.9 | 3.4 |
December | 0.8 | 0.4 | 1.2 | 0.8 | 0.5 | 0.5 | 0.6 | 1.7 |
|
0.001 | 0.001 | 0.001 | 0.001 | 0.001 | 0.001 | 0.001 | 0.001 |
LSD (0.05) | 0.61 | 0.51 | 0.16 | 0.31 | 0.21 | 0.14 | 0.33 | 0.51 |
Fruit (small, medium, and large pods) production started in April and peaked in August. Comparing the fruit pod sizes, there were significant (
Changes in pod sizes during the study period.
Small pods, which formed about 80% of the total fruits produced peaked in production in August. Except in July, small pods production formed the highest number in all the remaining months. Significant production of medium and large pods started in July with the medium pods being in greater numbers than the large pods. Whereas medium pods production peaked in August, that of large pods peaked in October. The rate of production of new pods and pod losses through abortion was similar between the months of April and June. However, the rate of pod abortion greatly exceeded the rate of new pods production from July to December (Figure
Levels of new pods and aborted fruits.
Between April and July, total fruit production and number of diseased pods were similar but deviated between August and October when the number of diseased pods exceeded total fruit production (Figure
Contrast in fruit production and diseased pods.
Significant relationships were found between flower production and climatic factors namely temperature, light intensity and rainfall. Temperature positively affected production of floral buds (
Relationship between temperature and the rate of mature floral buds, and open flowers. Data on the floral parts were square root transformed
Effect of Rainfall on production of mature floral buds and open flowers. Data on the floral parts were square root transformed
Effect of light intensity on production of mature floral buds and open flowers. Data on the floral parts were square root transformed
The present study has established that cocoa exhibits a season-related phenological pattern of flowering and fruit set involving overlapping cycles. Similar findings have been found in other tropical tree species [
The observation that fruit production and fruit abortion increased during the rainy season is corroborated by Valle et al. [
The tree-to-tree differences in the production of floral buds, opening of flowers, and formation of cherelles are consistent with the findings that cocoa flower initiation, shape and morphogenesis though dependent on the environment is regulated endogenously [
The observed levels of diseased pods in the area suggests that disease occurrence was a major determinant of final cocoa yield levels in commercial plantations, in spite of the fact that pollination successes largely determined the initial levels of fruit-set. This finding is in agreement with the observations made in La Lola, Costa Rica [
The Amazonia cocoa, the variety in the present study, has a longer spread of flowering due to the fact that the branches and trunks flower in turns, a phenomenon akin to the “manifold” (a term first used by [
Flowering of the cocoa trees in the study farms were affected by exogenous factors such as rainfall, temperature, and light. However, rainfall was found to be the most critical factor in the floral phenology of cocoa since it accounts for 78% and 75% of the variation in the production of mature floral buds and open lowers, respectively. All the ten study farms were exposed to the sunlight as there were no shade trees, though there was self-shading in the mature trees due to unbroken canopies, thus modifying the light intensity and temperature. Absence of shade cover may condition cocoa trees throughout the year to flower at irregular intervals, that is, a phenological pattern far less indicative of a response to seasonal changes in rainfall and other climatic conditions [
The fact that the cocoa flowered from the beginning of the raining season probably meant that cocoa reacts to the stimulus of water. This assertion was based on the observation that during the dry seasons (January through March) and before the onset of the rains in April there were no buds, flowers, or new pods on any of the tree trunks. It could be said generally that both genetic and physiological (intrinsic) factors are the primary factors responsible for basic timing of flowers whereas the environmental or extrinsic controls are the modifying factors. Ewusie [
The floral phenological patterns observed in the present study provide some advantage for cocoa reproduction and productivity. The main pollinators, biting midges (Ceratopogonidae), and gall midges (Cecidomyiidae), which are moisture-loving dipterans, are known to increase in population during the rainy months (May to July) when flower setting reaches a peak, and much less in the dry seasons [
The study has demonstrated that cocoa like all tropical tree species in general exhibit season-related phenological patterns of flowering but unlike most tropical plants, flowering is at the height of the long rainy season. In addition, fruit-set involved overlapping cycles (the phenophases of flowering, fruiting, and leaf-formation and leaf-fall more than once a year) under both intrinsic and extrinsic controls. Rainfall, as an extrinsic factor, was found to be the most critical in the floral phenology. The floral phenological pattern coincided with the activity of the main pollinators of cocoa which resulted in enhanced reproductive capacity for increased production of cocoa.