Climate change is likely to adversely affect production of cocoa around the world, but farmers are unprepared and more research is needed to help develop mitigation strategies and new varieties that can cope with drought
This article first appeared in the January ’18 issue of C&CI, click on subscribe now if you wish to read other informative articles in the January and future issues of C&CI.
November saw the first International Symposium of Cocoa Research (ISCR) take place in Lima, Peru, an event at which climate change – and its potential effects on the cocoa sector – were addressed in a number of papers. Those papers suggest that, despite the best efforts of the cocoa and chocolate industry, climate change could make deforestation more likely, and threaten farmers’ ability to sustain production.
Christian Bunn, Mark Lundy, Peter Läderach and Fabio Castro from the International Centre for Tropical Agriculture (CIAT) noted that global climate models project a continued increase in temperatures and changes in the spatial and temporal distribution of precipitation. These developments have been shown to potentially impact cocoa production in its most important origins. As they also noted, the prospect of reduced cocoa yields on existing plantations has led to renewed concern that producers could react by cutting down forest to create new areas in which to grow cocoa.
“We modelled the global distribution of suitable climates for cocoa production under historic and future conditions,” the CIAT scientists told the conference. “Model evaluation on historic data showed an ability to correctly identify current producing regions. We extrapolated climate data from multiple global climate models for mid- and end-of-century projections. Across all cocoa origins a reduction in climatic suitability for cocoa production were projected.
Area suitable for growing cocoa will diminish
“We found that the available area suitable for growing cocoa will diminish whilst areas with low suitability might be increasingly available. We also found that the projected impact of climate change is unlikely to make major cocoa producing regions altogether unsuitable in future.” Unfortunately, CIAT’s research also found that areas most likely to retain high suitability were found in the proximity of forest reserves where precipitation is most likely to remain sufficiently high.
“Climate change is likely to cause additional challenges to the sector at global scale,” said the CIAT scientists. “Research should focus on the impacts of high temperatures on quality and vitality of the plant, and the management of increased drought risk. The implications of changed climate conditions for regional pest and disease patterns remain uncertain.
“We conclude that cocoa production will continue to threaten biodiverse forests across tropical countries,” said the CIAT scientists. “Cocoa production is a primary beneficiary of ecosystem services provided by resilient landscapes. Deforestation will exacerbate the effects of climate change by resulting in locally reduced precipitation, additional emissions from land use change, and diminished barriers to pest and disease spread.” Efforts to make cocoa ‘deforestation free’ would, they argued, be particularly important.
How might climate change affect cocoa trees?
Scientist at Reading University in the UK described work they have been doing on the impact of climate change variables on vegetative and reproductive development in cocoa and the development of six genotypes of cacao.
They told delegates that, whilst climate change has the potential to affect cocoa production, limited research has been performed examining the impact these environmental changes are likely to have on cocoa physiology and yield, and the potential to identify genetic variation in responses. They presented data from the culmination of a five-year, greenhouse-based research project on the effects of elevated CO2 (ECO2) and water deficit stress in mature pod-bearing clones (CL 19/10, ICS 1, IMC 67, POUND 7/B, SCA 6, SPEC 54/1).
Trees were grown in pots for two years under CO2 enrichment (700 ppm) and limited soil moisture. Overall, water deficit caused a reduction in photosynthesis, stomatal conductance and various growth parameters, and an increase in water-use efficiency (WUE). Stem diameter increment, photosynthesis, quantum efficiency and WUE increased significantly in response to ECO2. The decline in quantum efficiency due to water stress was less severe in plants subject to elevated CO2 compared to the ambient CO2 treatment.
Water stress will be an issue
Similarly, the water deficit treatment resulted in a significant increase in WUE which was further enhanced under ECO2 in particular genotypes. In mature clones, the effects of ECO2 on pod development were not apparent until the second year of exposure. Pod size and the weight of certain pod components (husk, total and single bean weight) increased at ECO2. Water deficit caused a decrease in pod development in the first year of exposure but not the second, suggesting a potential adaptive response to water stress. Genetic differences in fatty acid responses to elevated CO2 were evident in SCA 6 and POUND 7/B. Genotypic variation in quantum efficiency, WUE and biomass partitioning between leaves and stems was also identified.
Overall, ECO2 had a positive effect on a number of growth and photosynthetic parameters in cocoa and it appears that ECO2 could play an important role mitigating against some of the negative impacts of water deficit stress through enhancement of WUE. A new project is now under way at the University of Reading which builds upon this research. It aims to identify the physiological basis for tolerance to water deficit and high temperature stress. The interactive effects of ECO2 and high temperature stress will be explored and screening tools developed to speed up the identification of more resilient germplasm. Using data from past and ongoing research, models will be developed to predict physiological and yield responses to varying climate conditions.
Making use of genetic diversity
Representatives of Bioversity International described work they have been doing on cocoa’s genetic diversity for resilience to climate change. Viviana Medina, Brigitte Laliberte, Stephan Weise and Jacob van Etten told delegates about models they have been using to evaluate the impact of climatic variations on cocoa production – the models acknowledge that decreased precipitation and increased temperatures will affect cocoa the most.
“While these models state with high degree of confidence a somewhat devastating future,” said Bioversity International, “many of the tolerance mechanisms and adaptation responses in the genetic diversity of cocoa are still little understood and have yet to be fully evaluated and included in breeding programmes.” Cultivation cannot just rely on increasing irrigation, or on moving to new areas and on deforestation, they said. “Maximizing current production areas by integrating climate ready management practices and resilient planting materials is a solution.”
Their paper presented the current status of research on cocoa and abiotic stresses focusing on increased drought, heat and CO2 tolerance, and the role of genetic diversity for greater resilience. It laid out model predictions of climate change on cocoa suitability and production, and discussed the importance of validating prediction models with physiological modelling. It identifies the gaps and proposes future collaborative research, new areas of modelling and research to be further explored towards identifying novel and tolerant genetic material, using big data analysis and crowd sourcing.
New varieties will need to be drought tolerant
“These approaches not only ensure the participation of farmers in the efforts of to identify resilient planting material, but also the opportunity to explore a wide range of genetic diversity exposed to contrasting climatic conditions in farmers’ fields. This is important given that the bulk of the data suggests that the extent of how drought or heat affects cocoa is determined by the individual genotype’s inherent traits that allow avoidance, tolerance or escape.
Potential for resilience
“If genetic diversity is fully exploited, for development of improved planting materials, both by research institutes and farmers, there is great potential for increased cocoa resilience through selective breeding, and identification of tolerant genotypes. The key lies in tapping the genetic potential of cocoa as a way to fully understand production limits and constraints,” they argued.
Virupax Baligar, Alex-Alan Almeida Dario Ahner, Enrique Arévalo-Gardini, Ricardo Goenaga and Zhenli He from the US Department of Agriculture’s Agricultural Research Centre also discussed the impact of drought on cocoa genotypes, in Brazil, Peru and Puerto Rico. They were in agreement with other speakers at the event that drought is potentially one of the most limiting abiotic stress factors for cocoa growth, development and production.
“Climatic changes that are occurring in the tropics, such as inconsistent and reduced rainfall patterns, and high temperatures in many cocoa growing regions has affected yields, raising major concerns for sustaining production,” they said. Echoing comments by other speakers, they said little is known about cocoa’s ability to adapt to drought.
Urgent need to identify genotypes
“There is an urgent need to identify genotypes with drought tolerance,” they told delegates, noting that most of the current cocoa germplasm has not been screened for either short or prolonged drought tolerance.
They described a series of greenhouse and growth chamber experiments undertaken to assess drought effects on early cacao morphological and physiological parameters and nutrient use efficiency of elite cocoa genotypes in Brazil, Peru and Puerto Rico.
Their findings showed that drought considerably affects the morphology (leaf, stem, and root parameters), physiology (photosynthesis, water use efficiency) and macro- nutrient use efficiency of cocoa. Genotypes showed various degrees of intra-specific variations for growth, physiology and nutrient use efficiency.
“Understanding plant growth, morphology, physiology and nutrient use efficiency traits influenced by drought will help in identification of genotypes that are tolerant to drought,” said the ARS researchers. “Such drought tolerant genotypes could be used in crop improvement programmes to evolve superior cultivars for any given drought stressed ecosystem.”■ C&CI
(photo: Neil Palmer, CIAT)