Search

Cocoa, Theobroma cacao, is an important tropical perennial crop grown widely in the humid\ud tropics. The exchange of cocoa germplasm between germplasm collections and breeding centres is\ud vital for varietal development. Intermediate quarantine facilities, such as the International Cocoa\ud Quarantine Centre, Reading UK (ICQC-R) play a vital role in ensuring the transfer of germplasm\ud whilst minimising the risk of spreading pests and diseases. Current screening procedures combine\ud visual inspection and molecular techniques, which are effective in detecting Cocoa swollen shoot\ud virus (CSSV), a badnavirus, which causes severe losses but are restricted to West Africa. However,\ud the detection of latent or mild virus infections that produce no visual symptoms has been a challenge.\ud Recently two badnavirus species of cocoa producing mild symptoms, cacao mild mosaic virus\ud (CaMMV) and cacao yellow vein-banding virus (CYVBV), have been sequenced. Here, we report\ud new assays for the detection of these two species, for the first time in non-symptomatic accessions.\ud Evolutionary and bioinformatic analyses of the viruses suggest their most recent source was from\ud Trinidad, though there is historic evidence that these viruses may have their origin in South America\ud and then become widespread globally over the last century. We also report a novel colorimetric\ud Loop-mediated isothermal amplification (LAMP) assay for the detection of CYVBV. This simple and\ud accurate method could be employed in field virus testing.

Cocoa mirids are the most important insect pests of cocoa in West Africa. This study investigated the effect of environmental parameters that are modulated by overhead shade, i.e. light intensity and temperature, on nutrient and phenolic concentrations in cocoa and their subsequent effect on mirid feeding. Eight-month-old cocoa seedlings were maintained for 50 days in two growth chambers set to day temperatures of 25oC or 30oC. Each chamber had sections with different light intensities (541, 365 and 181 µmolm-2s-1 PAR). For the field studies at Akim-Tafo in Ghana, eight-month-old plants of three cocoa clones were subjected to shaded (PAR= 180 µmol m-² s-1, between 11:00 and 12:00) and unshaded (PAR= 1767 µmol m-² s-1 between 11:00 and 12:00) treatments for 50 days after which nutrient measurements and mirid choice tests were carried out. No significant effect of environment was observed on the phenolic concentration of stems under controlled environment chamber conditions. However, in the field, the phenolic concentration of stems was significantly greater for unshaded compared with shaded plants (P=0.04). Under controlled conditions, the leaf nitrogen concentration increased slightly with light intensity (P=0.003). The same trend was seen in stems but only at 30oC. In the field, the impact of overhead shade on nitrogen varied between cocoa clones. The concentration of carbohydrates in both leaves and stems in the field was higher under unshaded conditions. When subjected to feeding tests, stems from unshaded cocoa had significantly more mirid feeding lesions (P=0.003) after 24 hours exposure to mirids compared to shaded cocoa. Mirid feeding therefore appears not to be deterred by the higher phenolic levels but rather there was a preference for cocoa tissue grown under unshaded conditions. These findings highlight the need to consider the growing environment of cocoa clones when screening for varieties with resistance to mirids.

Establishment of young cacao trees in West Africa can be severely impeded by the on-set of the dry season. To address this issue, a field experiment was conducted in Ghana to examine whether different mulch treatments and irrigation applied during the dry season combined with over-head shade could improve survival, early growth and yield of cacao. The mulch treatments used were polyethylene film and coffee husks placed around the young plants. Irrigation was used as a positive control and no mulching or irrigation was a negative control. Three shade regimes were provided through different arrangements of Gliricidia sepium and plantains. Four different cacao clones were used in the study in a replicated split-plot design. Early growth of cacao was stimulated under the irrigation and plastic mulch treatments. Higher rates of photosynthesis during the dry season appeared to underlie these increases. Significantly higher early yields were also observed under the irrigation and coffee mulch treatments compared to the control. Plant survival varied significantly between treatments; irrigation was associated with the highest plant survival (94%), followed by the plastic mulch treatment (91%), coffee husk (82%) and the control (70%). There was also an increase in survival when more intense shading was used. Under zero mulch conditions, differences in survival were observed between clones. The clones P 30 [POS] and SCA 6 were more sensitive to drought (in terms of survival) than PA 150 and T 79/501. It is concluded that relatively simple mulching techniques or controlled irrigation in conjunction with appropriate shade management can significantly improve early establishment and cropping of cacao.

Cocoa (Theobroma cacao L.) originated in South America, but is now cultivated in various parts of the tropics. Movement of cocoa germplasm is often required in breeding programmes to increase the genetic diversity pool or to test clones/progeny in the field. However, such movement brings with it the risks of spread of pests and diseases, many of which are confined to particular geographical locations. Thus, it is critical that movement of germplasm is conducted within a quarantine framework. This chapter reviews the risks associated with the movement of cocoa germplasm. It considers international governance of plant movement and discusses the International Cocoa Quarantine Centre at the University of Reading (ICQC,R) as a hub for safe handling and movement of cocoa germplasm.

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 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 ($310.00) while 8.0% were poor with less than GH¢ 801.62 ($398.81). An amount of money ranging from GH¢ 20.00 ($9.95) to GH¢ 89.04 ($44.29) per annum was needed to lift the 4.7% of cocoa farmers out of extreme poverty, which could be achieved through modest increases in productivity. The study highlighted how agricultural intervention programmes, such as CODAPEC, have the potential to contribute to improved farmer livelihoods.

The future of the world cocoa economy depends on the availability of genetic diversity and the sustainable use of this broad genetic base to breed improved varieties. Decreasing cacao genetic diversity (in situ, on-farm and conserved in collections) is a serious problem and all its many causes need to be urgently addressed: the destruction of the Amazonian rainforests, changing patterns of land use, the spread of pests and diseases, sudden changes in climate, and threats from natural disasters and extreme weather. These factors are resulting in an irreversible loss of the cacao genetic diversity so essential for farmers, breeders, and consumers. Most of the countries involved in the improvement and production of cacao are highly dependent on genes and varieties characterized and conserved in other countries and regions. Effective management of cacao genetic resources can therefore only be carried out through international collaboration. A considerable portion of the global cacao diversity is in situ, in farmers' fields and held in genebanks around the world, including two international collections maintained at the Cocoa Research Centre of the University of the West Indies (CRC/UWI), Trinidad and Tobago, and at the Centro Agronómico Tropical de Investigación y Enseñanza (CATIE), Costa Rica. Unfortunately, much of the genetic resources maintained in national collections is under-used or at risk, and funding remains insufficient and unstable. The vision of the Global Strategy for the Conservation and Use of Cacao Genetic Resources is to improve the livelihoods of the 5-6 million farmers in developing countries across tropical Africa, Asia and Latin America and the 40-50 million people who depend upon cocoa for their livelihoods. The specific goal is to optimize the conservation and maximize the use of cacao genetic resources as the foundation of a sustainable cocoa economy. This it does by bringing together national and international players in public and private sectors. The expected outputs are: (1) the cacao genepool is conserved in situ and ex situ for the long term by a global network of partners, (2) the global system for the safe exchange of cacao germplasm is strengthened, (3) the use of cacao genetic diversity is optimized and (4) the effectiveness of global efforts to conserve and use cacao genetic resources is assured. To ensure these outputs are implemented, the first and urgent task will be to secure funding for the existing cacao genetic diversity currently maintained in ex situ collections and accessible in the public domain. CacaoNet will work towards the establishment of an endowment fund for the conservation and use of the most valuable resources in perpetuity. At the centre of the Global Strategy is the Global Strategic Cacao Collection (GSCC): a "virtual genebank" of accessions of highest priority for conservation, wherever they are physically located. The accessions will be selected to capture the greatest range of genetic (allelic) richness and key traits of interest to users. The inclusion of materials in the GSCC will be on the basis that governments concerned will be willing to place them in the public domain, and will take the necessary political and legal steps to do so and thus to make this material available to users worldwide. The Global Strategy, developed by the Global Network for Cacao Genetic Resources (CacaoNet), is the result of a consultation process that drew upon the global cocoa community's expertise in all aspects of cacao genetic resources. It provides a clear framework to secure funding for the most urgent needs to ensure that cacao diversity is conserved, used and provides direct benefits to the millions of small-scale cacao farmers around the world.

A range of physiological parameters (canopy light transmission, canopy shape, leaf size, flowering and flushing intensity) were measured from the International Clone Trial, typically over the course of two years. Data were collected from six locations, these being: Brazil, Ecuador, Trinidad, Venezuela, Côte d’Ivoire and Ghana. Canopy shape varied significantly between clones, although it showed little variation between locations. Genotypic variation in leaf size was differentially affected by the growth location; such differences appeared to underlie a genotype by environment interaction in relation to canopy light transmission. Flushing data were recorded at monthly intervals over the course of a year. Within each location, a significant interaction was observed between genotype and time of year, suggesting that some genotypes respond to a greater extent than others to environmental stimuli. A similar interaction was observed for flowering data, where significant correlations were found between flowering intensity and temperature in Brazil and flowering intensity and rainfall in Côte d’Ivoire. The results demonstrate the need for local evaluation of cocoa clones and also suggest that the management practices for particular planting material may need to be fine-tuned to the location in which they are cultivated.

Cocoa variety selection and breeding are necessarily long-term activities. Collaboration between research centres is needed to find durable solutions to global production constraints, such as losses due to spreading diseases and pests, and to bridge the gaps between the main cocoa germplasm collection centres, which are in the Americas, and the main areas of cocoa production that are currently in Africa and Asia. Farmer participatory approaches to selection of new cocoa varieties allow integration of farmers' knowledge in breeding programmes and are expected to enhance the adoption rate of new cocoa varieties. These were the main rationale behind the activities carried out in two successive CFC/ICCO/Bioversity projects called "Cocoa Germplasm Utilisation and Conservation, a Global Approach (1998-2004)" and "Cocoa Productivity and Quality Improvement, a Participatory Approach (2004-2010)". The projects were mainly funded by the CFC1, executed by Bioversity International, and implemented under the auspices of ICCO. They received substantial co-funding from BCCCA (now CRA), CIRAD, Guittard, Mars, USDA and WCF and significant counterpart contributions from all 14 collaborating institutions. An overview is presented of the activities carried out and results obtained. More than 120 ha of new cocoa variety trials were established on-station and 60 ha of on-farm observation plots. At all sites, numerous clone and hybrid varieties were selected and at some sites multiplication and/or distribution of these varieties to farmers has been initiated. Approximately 2000 promising farm selections are being compared with the best breeders' selections in on-station observation trials and in the on-farm variety trials. Genetic diversity of more than 2000 farm selections in Africa was analysed through co-financing arrangements and results published. Varieties with high levels of resistance to major diseases (Phytophthora pod rot or Ppr, witches' broom and moniliasis) were selected in the pre-breeding programmes carried out in the international cocoa germplasm collections held by CRU and CATIE as well as in cocoa producing countries. Transfer of selected germplasm to interested user countries, through intermediate quarantine at Reading University, is in an advanced stage. Rapid and/or early resistance screening methods have been validated and successfully adopted for Ppr, while screening for resistance to other diseases and pests continues to rely mainly on field evaluations. The International Clone Trial (ICT), planted at nine sites, is yielding important information on stability of all economically important traits. Preliminary results on flavour traits analysed for ten ICT clones show predominant country effects for basic flavour traits and significant interactions for fruity and floral flavour traits. The project has provided ample opportunities for training of young cocoa breeders and for exchange of information through regular regional and international workshops. The need is stressed for continuation of the collaborative efforts carried out with support from the 2 CFC/ICCO/Bioversity projects and for sustainable long-term funding of cocoa conservation, evaluation and breeding activities.

A range of physiological parameters (canopy light transmission, canopy shape, leaf size, flowering and flushing intensity) were measured from the International Clone Trial, typically over the course of two years. Data were collected from six locations, these being: Brazil, Ecuador, Trinidad, Venezuela, Côte d’Ivoire and Ghana. Canopy shape varied significantly between clones, although it showed little variation between locations. Genotypic variation in leaf size was differentially affected by the growth location; such differences appeared to underlie a genotype by environment interaction in relation to canopy light transmission. Flushing data were recorded at monthly intervals over the course of a year. Within each location, a significant interaction was observed between genotype and time of year, suggesting that some genotypes respond to a greater extent than others to environmental stimuli. A similar interaction was observed for flowering data, where significant correlations were found between flowering intensity and temperature in Brazil and flowering intensity and rainfall in Côte d’Ivoire. The results demonstrate the need for local evaluation of cocoa clones and also suggest that the management practices for particular planting material may need to be fine-tuned to the location in which they are cultivated.

The level of mislabelling of cocoa clones in germplasm collections is fairly high. Although not a new problem, the availability of genetic fingerprinting technologies has allowed projects to be developed that use microsatellite markers to compare clones. However, it is important that when clones with the same name are found to have different profiles, one is determined to be the true type (with reference to the most original material). Off-types should be kept for their potential agronomic value, but with a unique new name. We have proposed a format for renaming that highlights the mislabelling event and which includes references to the source germplasm collection and the name originally given to the clone.

The CacaoNet Technical Guidelines for the Safe Movement of Cacao Germplasm provide updated information on the precautions and quarantine measures that can be taken to minimise the risk of spread of pests and diseases when cacao genetic resources are being moved for research, crop improvement, plant breeding, exploration or conservation. These Guidelines are based on those last published by FAO/IPGRI in 1999 but have been revised and expanded by a group of experts set up within CacaoNet (the Global Cacao Genetic Resources Network coordinated by Bioversity International), to take account of new knowledge of the pests and diseases, including their current distribution, and advances in detection techniques. These CacaoNet Guidelines were first published on-line in 2012 but have been revised in 2014, in 2017 and now in 2021 to take account of new information received. The document includes general advice regarding safe procedures to use when moving cacao germplasm, whether as seed, vegetative and tissue cultured materials, and summarised information on the geographical spread and risks posed by significant pests and diseases of cacao. In addition, experts have contributed sections giving detailed information on the following: Virus diseases (Cacao necrosis virus, Cacao swollen shoot virus (CSSV), Cacao Yellow mosaic virus), Fungal diseases (Witches’ broom disease, Moniliophthora pod rot, Phytophthora pod rot, Vascular streak die-back, Verticillium wilt, Ceratocystis wilt, Rosellinia root rot), Insect pests (Cocoa pod borer, mirids/capsids, mosquito bug, other insect pests) and nematodes. Each section contains information on physical symptoms, geographical distribution, biology of the pest or disease and recommended quarantine measures. The publication of these Guidelines has been supported by financial and in-kind contributions from Bioversity International, the CGIAR Research Programme on Forests, Trees and Agroforestry, the Cocoa Research Association Ltd., UK (CRA Ltd., a UK-based organization managing scientific cocoa research on behalf of Mars Mondelēz International and the London Cocoa Trade NYSE-Liffe) and the University of Reading. CacaoNet has received additional financial support from Mars, the U.S. Department of Agriculture, Agricultural Research Service (USDA/ARS) and the World Cocoa Foundation (WCF).