Andrew Daymond

Genotypic variation in photosynthesis in cacao is correlated with stomatal conductance and leaf nitrogen

Variation in photosynthetic parameters was observed between eight contrasting cacao (Theobroma cacao) genotypes. Net photosynthetic rate (PN) ranged from 3.4 to 5.7 μmol(CO2) m−2 s−1 for the genotypes IMC 47 and SCA 6, respectively. Furthermore, genotypic differences were detected in quantum efficiency ranging from 0.020 to 0.043 μmol(CO2) μmol−1(photon) for UF 676 and AMAZ 15/15, respectively. Differences in PN were correlated with both stomatal conductance (gs) and leaf nitrogen per unit area. Some variation in water use efficiency was observed between genotypes, both intrinsic (PN/gs) and instantaneous (PN/transpiration rate). Both measures of water use efficiency were a negative function of specific leaf area. Evidence was found for a trade-off mechanism between cacao genotypes in photosynthesis and leaf structure. High photosynthetic rate, expressed on a mass basis was associated with smaller leaves. Furthermore, thinner leaves were compensated for by a higher nitrogen content per unit mass.

PHOTOSYNTHETIC ACTIVITY AND EARLY GROWTH OF FOUR CACAO GENOTYPES AS INFLUENCED BY DIFFERENT SHADE REGIMES UNDER WEST AFRICAN DRY AND WET SEASON CONDITIONS

The physiological performance of four cacao clones was examined under three artificial shade regimes over the course of a year in Ghana. Plants under light shade had significantly higher photosynthetic rates in the rainy seasons whereas in the dry season there was a trend of higher photosynthetic rates under heavy shade. The results imply that during the wet seasons light was the main limiting factor to photosynthesis whereas in the dry season vapour pressure deficit was the major factor limiting photosynthesis through stomatal regulation. Leaf area was generally lower under heavier shade but the difference between shade treatments varied between clones. Such differences in leaf area allocation appeared to underlie genotypic differences in final biomass production in response to shade. The results suggest that shade for young cacao should be provided based on the current ambient environment and genotype.

CANOPY CHARACTERISTICS OF CONTRASTING CLONES OF CACAO ( THEOBROMA CACAO )

Canopy characteristics (leaf area index, fractional light interception, extinction coefficient) of mature trees of ten clonally propagated cacao cultivars were measured over a period of 14 months at an experiment site in Bahia, Brazil. Differences in leaf area index between clones became more pronounced over time. When an approximately constant leaf area index was reached (after about nine months), the leaf area index varied between clones from 2.8 to 4.5. Clonal differences in the relationship between leaf area index and fractional light interception implied differences in canopy architecture, as reflected by the range of extinction coefficients (mean values ranged from 0.63 for the clone TSH-565 to 0.82 for CC-10). The results demonstrate the potential for breeding more photosynthetically efficient cacao canopies.

Knowledge and perception of Ghanaian cocoa farmers on mirid control and their willingness to use forecasting systems

Annual losses of cocoa in Ghana from mirids are significant; therefore, accurate timing of insecticide application is critical to enhance yields. However, cocoa farmers often lack information on the expected mirid population for each season to enable them to optimize pesticide use. This study assessed farmers’ knowledge and perceptions of mirid control and their willingness to use forecasting systems informing them of the expected mirid peaks and the time of pesticide application. A total of 280 farmers were interviewed in the Eastern and Ashanti regions of Ghana with a structured open- and closed-ended questionnaire. Most farmers (87%) considered mirids the most important insect pest on cocoa, with 47% of them attributing 30–40% of annual crop losses to mirid damage. There was a wide variation in the timing of insecticide application as a result of farmers using different sources of information to guide the start of application. The majority of farmers (56%) did not have access to information about the type, frequency and timing of insecticide use. However, respondents who were members of farmer groups had better access to such information. Extension officers were the preferred channel for information transfer to farmers, with 72% of farmers preferring them to other available methods of communication. Almost all the respondents (99%) saw the need for a comprehensive forecasting system to help farmers manage cocoa mirids. The importance of the accurate timing of mirid control based on forecasted information to farmer groups and extension officers is discussed.

Optimizing mirid control on cocoa farms through complementary monitoring systems

Mirids (Sahlbergella singularis and Distantiella theobroma) are the most important insect pests affecting cocoa production across West Africa. Understanding the population dynamics of mirids is key to their management; however, the current recommended hand‐height assessment method is labour intensive. The objective of the study was to compare recently developed mirid sex pheromone trapping and visual hand‐height assessment methods as monitoring tools on cocoa farms and to consider implications for a decision support system. Ten farms from the Eastern and Ashanti regions of Ghana were used for the study. Mirid numbers and damage were assessed fortnightly on twenty trees per farm, using both methods, from January 2012 to April 2013. The mirid population increased rapidly in June, reached a peak in September and began to decline in October. There was a significant linear relationship between numbers of mirids sampled to hand‐height and mirid damage. High numbers of male mirids were recorded in pheromone traps between January and April 2012 after which there was a gradual decline. There was a significant inverse relationship between numbers of trapped adult mirids and mirids sampled to hand‐height (predominantly nymphs). Higher temperatures and lower relative humidities in the first half of the year were associated with fewer mirids at hand‐height, but larger numbers of adult males were caught in pheromone traps. The study showed that relying solely on one method is not sufficient to provide accurate information on mirid population dynamics and a combination of the two methods is necessary.

The impact of elevated CO2 and water deficit stress on growth and photosynthesis of juvenile cacao (Theobroma cacao L.).

Atmospheric CO2 concentration continues to rise and is predicted to reach approximately 700 ppm by 2100. Some predictions suggest that the dry season in West Africa could be extended with climate change. This study examined the effects of elevated CO2 concentration and water deficit on growth and photosynthesis of juvenile cacao. Light-saturated photosynthesis (Pmax), quantum efficiency, and intrinsic water-use efficiency increased significantly in response to elevated CO2, as did a range of growth and development responses (e.g. leaf area and leaf number), but the magnitude of the increase was dependent on the water treatment. Stomatal index was significantly greater in the elevated CO2 treatment; an atypical response which may be a reflection of the environment in which cacao evolved. This study shows a positive effect of elevated CO2 on juvenile cacao which may help to alleviate some of the negative impacts of water deficit stress.

Farmers' perceptions of the effectiveness of the Cocoa Disease and Pest Control Programme (CODAPEC) in Ghana and its effects on poverty reduction.

The study examined the contribution of the Cocoa Disease and Pest Control Programme (CODAPEC), which is a cocoa production-enhancing government policy, to reducing poverty and raising the living standards of cocoa farmers in Ghana. One hundred and fifty (150) cocoa farmers were randomly selected from five communities in the Bibiani-Anhwiaso-Bekwai district of the Western Region of Ghana and interviewed using structured questionnaires. Just over half of the farmers (53%) perceived the CODAPEC programme as being effective in controlling pests and diseases, whilst 56.6% felt that their yields and hence livelihoods had improved. In some cases pesticides or fungicides were applied later in the season than recommended and this had a detrimental effect on yields. To determine the level of poverty amongst farmers, annual household consumption expenditure was used as a proxy indicator. The study found that 4.7% of cocoa farmers were extremely poor having a total annual household consumption expenditure of less than GH¢ 623.10 (

The influence of shade and organic fertilizer treatments on the physiology and establishment of Theobroma cacao clones

310.00) while 8.0% were poor with less than GH¢ 801.62 (

Postharvest sprouting of onion bulbs grown in different temperature and C02 environments in the UK

398.81). An amount of money ranging from GH¢ 20.00 (

The effects of temperature and light integral on early vegetative growth and chlorophyll fluorescence of four contrasting genotypes of cacao (Theobroma cacao)

9.95) to GH¢ 89.04 (