Assessment of morphological, physiological and molecular characteristics of cocoa accessions from Central and South America in relation to drought tolerance

Eleven cocoa accessions, representing collections from five central and south American countries, were assessed for their morphological, molecular and physiological parameters. Growth characters were observed in three year old plants and initial pod yields were recorded. Photosynthesis, related parameters and chlorophyll indices, measured during two seasons, showed significant differences between non-stress and stress periods as well as among the genotypes. The transpirational water loss was reduced with increased stomatal closure, which is a favourable drought trait in crops. The results indicated that the genotypes showing higher water potential and Fv/Fm ratio can be considered as drought tolerant. The rank sums of these parameters showed that genotypes JA-1/19, POU-16/A and SC-4 were the most drought-tolerant. Microsatellite markers were used to assess the extent of genetic diversity between clones. The amplification of DNA from the 11 accessions using the 15 microsatellite loci revealed a total of 80 consistent and scorable alleles with an average of 5.33 alleles per locus and all the loci were 100 per cent polymorphic, the most polymorphic locus being mTcCIR33 with 8 alleles. The observed heterozygosity ranged from 0.36 to 0.63 with an average of 0.52. The inbreeding co-efficient (f) ranged from -0.22 (mTcCIR8) to 0.58 (mTcCIR40) with an average of 0.32. The microsatellite marker analysis revealed that the genotypes possess a wide genetic diversity. The drought tolerant types identified in this study viz., JA-1/19, POU-16/A and SC-4 could be used for cultivation in areas with moisture deficient stress and in selective cocoa breeding programs for drought tolerance

Assessment of morphological, physiological and molecular characteristics of cocoa accessions from Central and South America in relation to drought tolerance

Eleven cocoa accessions, representing collections from five central and south American countries, were assessed for their morphological, molecular and physiological parameters. Growth characters were observed in three year old plants and initial pod yields were recorded. Photosynthesis, related parameters and chlorophyll indices, measured during two seasons, showed significant differences between non-stress and stress periods as well as among the genotypes. The transpirational water loss was reduced with increased stomatal closure, which is a favourable drought trait in crops. The results indicated that the genotypes showing higher water potential and Fv/Fm ratio can be considered as drought tolerant. The rank sums of these parameters showed that genotypes JA-1/19, POU-16/A and SC-4 were the most drought-tolerant. Microsatellite markers were used to assess the extent of genetic diversity between clones. The amplification of DNA from the 11 accessions using the 15 microsatellite loci revealed a total of 80 consistent and scorable alleles with an average of 5.33 alleles per locus and all the loci were 100 per cent polymorphic, the most polymorphic locus being mTcCIR33 with 8 alleles. The observed heterozygosity ranged from 0.36 to 0.63 with an average of 0.52. The inbreeding co-efficient (f) ranged from -0.22 (mTcCIR8) to 0.58 (mTcCIR40) with an average of 0.32. The microsatellite marker analysis revealed that the genotypes possess a wide genetic diversity. The drought tolerant types identified in this study viz., JA-1/19, POU-16/A and SC-4 could be used for cultivation in areas with moisture deficient stress and in selective cocoa breeding programs for drought tolerance

The physiological responses of cacao to the environment and the implications for climate change resilience. A review

Cacao (Theobroma cacao L.) is a tropical perennial crop which is of great economic importance to the confectionary industry and to the economies of many countries of the humid tropics where it is grown. Some recent studies have suggested climate change could severely impact cacao production in West Africa. It is essential to incorporate our understanding of the physiology and genetic variation within cacao germplasm when discussing the implications of climate change on cacao productivity and developing strategies for climate resilience in cacao production. Here we review the current research on the physiological responses of cacao to various climate factors. Our main findings are 1) water limitation causes significant yield reduction in cacao but genotypic variation in sensitivity is evident, 2) in the field cacao experiences higher temperatures than is often reported in the literature, 3) the complexity of the cacao/ shade tree interaction can lead to contradictory results, 4) elevated CO2 may alleviate some negative effects of climate change 5) implementation of mitigation strategies can help reduce environmental stress, 6) significant gaps in the research need addressing to accelerate the development of climate resilience. Harnessing the significant genetic variation apparent within cacao germplasm is essential to develop modern varieties capable of high yields in non-optimal conditions. Mitigation strategies will also be essential but to use shading to best effect shade tree selection is crucial to avoid resource competition. Cacao is often described as being sensitive to climate change but genetic variation, adaptive responses, appropriate mitigation strategies and interactive climate effects should all be considered when predicting the future of cacao production. Incorporating these physiological responses to various environmental conditions and developing a deeper understanding of the processes underlying these responses will help to accelerate the development of a more resource use efficient tree ensuring sustainable production into the future

Response of coconut seedlings to elevated CO2 and high temperature in drought and high nutrient conditions

The interaction effect of climate change variables elevated CO2 and elevated temperature (ET) with drought and nutrients on growth and development of coconut seedlings was studied in an open top chamber (OTC) at Central Plantation Crops Research Institute (CPCRI), Kasaragod. Seedlings were exposed to ambient (normal CO2 and temperature), elevated CO2 (550 and 700 ppm), ET (3 °C above ambient) and ET + elevated CO2 (550 ppm CO2 + 3 °C). In each OTC, a set of seedlings were subjected to drought (50% FC) and another set was maintained at 150 per cent recommended dose of fertilizer (RDF). Seedlings in elevated CO2 treatments accumulated significantly higher biomass. It was 1.13 and 1.98 kg seedling-1 with 550 and 700 ppm CO2 respectively as against 1.10 in ambient treatment. It was the least in ET treatment (0.91). The stomatal conductance (gs) and transpiration (Tr) of plants grown under elevated CO2 was reduced without affecting the photosynthesis. As a consequence, the whole plant WUE of coconut seedlings grown under elevated CO2 was high both under control and drought condition. The WUE significantly reduced both in high temperature and drought stressed plants. Elevated CO2 to certain extent compensated for water stress and high temperature induced reduction in growth of coconut

Response of coconut seedlings to elevated CO2 and high temperature in drought and high nutrient conditions

The interaction effect of climate change variables elevated CO2 and elevated temperature (ET) with drought and nutrients on growth and development of coconut seedlings was studied in an open top chamber (OTC) at Central Plantation Crops Research Institute (CPCRI), Kasaragod. Seedlings were exposed to ambient (normal CO2 and temperature), elevated CO2 (550 and 700 ppm), ET (3 °C above ambient) and ET + elevated CO2 (550 ppm CO2 + 3 °C). In each OTC, a set of seedlings were subjected to drought (50% FC) and another set was maintained at 150 per cent recommended dose of fertilizer (RDF). Seedlings in elevated CO2 treatments accumulated significantly higher biomass. It was 1.13 and 1.98 kg seedling-1 with 550 and 700 ppm CO2 respectively as against 1.10 in ambient treatment. It was the least in ET treatment (0.91). The stomatal conductance (gs) and transpiration (Tr) of plants grown under elevated CO2 was reduced without affecting the photosynthesis. As a consequence, the whole plant WUE of coconut seedlings grown under elevated CO2 was high both under control and drought condition. The WUE significantly reduced both in high temperature and drought stressed plants. Elevated CO2 to certain extent compensated for water stress and high temperature induced reduction in growth of coconut

Net primary productivity, carbon sequestration and carbon stocks in areca-cocoa mixed crop system

Carbon sequestration by terrestrial biomass is one of the mitigation strategies reducing GHGs in the atmosphere. The areca-cocoa mixed crop not only ensures a sustainable crop production, but also serves as a good system for biomass production and carbon accumulation. Arecanut is grown either as mono-plantation or intercropped with other plantations like cocoa, banana, etc, whereas, cocoa is grown only as an intercrop of either coconut or arecanut. Areca-cocoa system had a standing biomass of 23.15, 54.09, 87.10 and 121.93 t ha-1 in 5th, 8th, 15th and 20th years of growth, respectively. Annual increments in biomass or net primary productivity ranged from 1.38-2.66 t ha-1 in cocoa and 3.34-7.11 t ha-1 in areca. Parallel to these, CO2 sequestration ranged from 2.02-3.89 and 5.14-10.94 in cocoa and areca respectively. The standing biomass increased over time indicating accumulation of biomass in stem and also due to increase in yield by arecanut and cocoa plants an age up to 20th year of planting. The study has thus revealed that the biomass and primary productivity is considerable with areca-cocoa mixed crop and comparable to any agro-forestry systems involving cocoa. Arecanut cocoa based cropping systems produce abundant biomass to qualify for carbon sequestration. In this paper, the net primary productivity in an arecanut-cocoa system in terms of biomass production, calculation by biomass models and carbon sequestration are discussed