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The prolonged dry seasons result in cocoa seed mortality, whereas short dry seasons result in decreased pod filling, which affect the size of the beans. The fluctuations of weather may cause serious environmental hazards.
In this chapter mainly shows the recent research works on cocoa.
Seasonal temperature is an important climatic factor which can have thoughtful effects on the yield of crops. Changes in seasonal temperature affect the grain yield, mainly through phenological development processes.
Temperature will be the primary factor to control cocoa production ,the effect of weather may produce serious pest/pathogen attack (Christisnsen, 1986). In the tropical cocoa growing areas temperature lies maximum of 30-320C and minimum of 18-210C and absolute minimum of 150C, due to unfavourable conditions the plant will get into leaf defoliation, reduced yields and pest/pathogen attack (Wood and Lass .1985)…
The changes in temperature will affect the phenological process of plant, phenology is an indicator of Global warming (Chmielewski and Rotzer 2000).
The Black pod disease will be most destructive one, around 50% of the cocoa farm crops were affected by serious Black pod disease. The disease is very much associated to Weather and climatic conditions (Idachaba & Olayide, 1976; and MASDAR, 1998). The studies made by Green Wood and Posner (1950) in Ghana reported that leaf flushing will be controlled by temperature, and the weekly mean of daily maximum temperature must be at least 28.30C for flushing initiated.
Wood and Lass (1985) studied that in the West Africa temperature vary more than any other cocoa growing countries. Daily, seasonal,annual differences of climatic and weather parameters having greater importance to plant growth (Ayoade, 2004).
Sale(1968)is noticed that at constant temperature 23.30C very little flushes were produced and at 300C most of the flushes are produced,An increase in day or night temperature it increases the number of flushes.
A reduction in flowering is observed in cocoa as temperature drops below 230C (Boyer,1970). Daymond and Hadley (2004) were found that 25 °C will be the optimum temperature for cacao photosynthesis.
(White. et al.,1999;Kramer et al.,2000) reported that The changes on weather variables might influence net photosynthesis,pollination,flowering and yield.several reports indicating similar impacts on weather changes in several other crops. Harun and Hardwick(1988) found that rate of photosynthesis changed between 200C and 300C.
Alvim (1966) reported that the environmental factors like Rainfal,temperature having more significance in flowering and pod setting .
Wood and Lass (1985) observed that in Ivory Coast Rainfall vary from 1200mm in the cocoa growing areas, and nearly 3,000 mm in West Cameron and Nigera.the major cocoa cultivating areas lies in between 1250mm and 2800mm.the annual rainfall may excess of 2500mm will lead to Vascular streak die back and other fungal diseases. In the cost of Venezuela cocoa growing under irrigation, the annual rainfall is lies between 850-1000mm.
The studies made by Adams and Mc Kelvie(1955) in Ghana most of the cocoa cultivating areas having a short, mild, dry season, cocoa was limited in those areas received rainfall more than 250mm in between November and March.
Purseglove(1974) is studied about the rainfall on cocoa cultivating areas to be 1010 to 2540mm . The effect in soil moisture on seedling growth were studied at Cocoa Research Institute, Ghana(CRI,1972).
(Jose et al., 2008; CPCRI,2015) found that around 90% of the yield loss is due to fruit rot disease, heavy rainfall will be the reason for fruit rot disease. Wood and Lass (1985 ) studied that the cocoa grows satisfactory in West Africa where the annual rainfall total is 1300-1500mm, West coast of India and Kerala the annual rainfall is exceeds to 3000mm,during the last five months of dry season cocoa must needed irrigation.
Well distributed rainfall that means above 1200mm a year is the most suitable for growth Asopa and Narayanan(1990). The plant requires an annual rainfall of 1500-2000mmfora minimum of 90-100mmper month(ICAR,2002).
Wood and Lass (1985) had observed higher relative humidity in cocoa cultivating areas, often 100% at night that falls to 70-80% by day, and sometimes lowers in the dry season, and the spread of fungal diseases and difficulties of storage and drying was also observed due to relative humidity.
In tropical environments under daylight conditions the temperature and relative humidity in the top two thirds of the canopy are comparable with the conditions of the surrounding atmosphere whereas these properties of the air at the canopy base are strongly decoupled (Shuttleworth et al.,1985).
High photosynthetically active radiation, low relative humidity and moisture stress lessens stomatal conductance in cocoa (Balasimha and Rajagopal, 1988).
Studies conducted by Harun and Hardwick (1988) regarding effect of temperature and water vapour deficits on photosynthesis and transpiration of cocoa leaves by using infrared analyzers observed a constant photosynthetic rate with low water vapour pressure deficit upto 10 m bar and also with an increasing water vapour pressure deficit. An increase in stomatal resistance was noted with increased water vapour pressure.
According to Dakwa (1977), the development of black pod disease (a highly infectious disease in cocoa,which can destroy a cocoa farm within eighteen to twenty-four (18-24) months which is caused by a fungus called phytophthora spp) in cocoa growing belt in West Africa was linked to relative humidity which was significantly correlated with the research conducted by him. However, the seemingly high number of farmers (91%) also agreed with the statement that the fact increasing black pod disease is highly aided by high rainfall (high humidity) into their farms.
Relative Humidity during morning and evening had a negative influence on flower production in cocoa plants and the maximum influence was noticed during the initial eight weeks prior to flowering (Prameela, 1997).
Alvim (1958) used the inﬁltration technique to display the degree of stomatal opening in cocoa, and showed, with cutting sand young plants, that the technique could be used as a practical indicator of water stress in cocoa. In a ﬁeld study with ﬁve-year-old plants, which were not suffering from water stress, stomatal opening increased as the light intensity increased with maximum opening in strong sunlight
Studies conducted by Soria(1970)in the two localities of tropical rainforest climatic conditions in Costa Rica regarding the annual flowering and pollination of cocoa. Couprie(1972) showed that the sunshine had a negative but non -significant result on fruit set and Cherelle wilt
The amount of sunlight that falls on cocoa tree will affect its growth and yield, a shade experiment is conducted in Trinidad show that 50% shade is optimum for young cocoa, but 50% of the shade in Trinidad allow quiet different amount of solar energy to fall on the tree as compared with 50% shade in Ghana (Wood and Lass ,1985)
Bright sunshine hours could enhanced flowering and maximum correlation noted seven weeks prior to flowering (Prameela,1997).
In cocoa the combined effect of solar radiation and wind could result in severe mechanical injuries at the pulvinous region (Alvim et al.,1972).
The violent wind and hurricane may reason for severe damage to basal chupon.in the case of young plants physical damages caused by wind blow in this case sensitivity of cocoa plant having greater importance,where suchwind occur should protected using wind breaks(Wood and Lass ,1985).
According to(Balasimha,2002) by varying intensity in different cocoa producing areas ,wind could cause undesirable effect on cocoa causing premature leaf fall. In west Africa harmattan-the dry wind which blows from the Sahara for a variable period between December and March causing Cherelle’s and flowers drop of in Ivory cost areas(WCF,2008).
Couprie (1972) observed the growth, flowering and fruiting characters of cocoa and found that the fruit set was negatively influenced by the cumulative maximum temperature of the proceeding two weeks. Boyer (1974) also reported a negative relation of fruit set to temperature.
Alvim et al. (1972) studied pod development in relation to temperature and concluded that the rate of pod development increased with increase in temperature.
Alvim (1981) reported that temperature played an important role in regions like Bahia where there is marked seasonal difference in temperature. Hassan et al. (1981) observed a significant positive correlation between the number of harvested pods and mean monthly maximum temperature five months before.
Alvim (1987) reported that in Bahia, the relatively low temperature from June to August was responsible for the lack of harvest from January to March, that is seven months after the cool period (mean temperature lower than 23oC)
Alvim (1965, 1968, 1981) reported that temperature affects the flowering intensity and lower than average temperature contributed to reduced flowering. Flowering was inhibited when the monthly mean temperature was below 23oC (Alvim, 1966).
Sale (1969) studied the flowering process of cocoa in relation to the temperature conditions in Trinidad, West Indies. It is observed that as compared to plants growing in regions with a day temperature of 23.3oC, plants in the regions with a day temperature of 26.6oC to 30oC had more active flowering cushions per plant and more number of flowers per cushion per week.
Couprie (1972) showed that flowering was greater when daily temperature variation was least. Mossu and Lotode (1977) found low temperature to be favourable for pollination.
Madhu (1984) noted that the mean monthly minimum and maximum temperature, one month previous to flowering affected the flower production.
Wood (1985) also reported the effect of temperature on flowering. He found that number of flowers increased as the temperature increased.
Flower production was positively correlated with maximum temperature and in the case of minimum temperature both positive and negative correlations were observed (Prameela, 1997).
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