Frances L. Bekele

Evaluation and utilisation of cacao (Theobroma cacao L.) germplasm at the International Cocoa Genebank, Trinidad

The aim of this study was to identify promising genotypes in the International Cocoa Gene bank, Trinidad (ICG,T) for use in cacao breeding. Subsets of the germ plasm collection were evaluated for bean number, bean weight, pod index (581 genotypes) and resistance to Phytophthora pod rot(500 genotypes). Among three groups of cacao assessed (For astero, Refractario and Trinitario), Trinitario had the highest percentage of genotypes (36.9%) with large bean weight (> 1.2 g), while For astero possessed the highest proportion of genotypes (22.6%) with a large number of beans (> 45). The ICS population had the highest percentage (44.1%) of genotypes with heavy beans, and IMC the highest percentage of genotypes with large bean number (68.6%). A low, but significant negative correlation (r = –0.19, p≤ 0.001) between bean number and bean weight suggests that an increase in bean number may repress an increase in bean weight and vice versa. However, inten genotypes good values of bean weight and number were combined demonstrating that selection for both large bean number and bean weight is possible. The highest percentage (28.1%) of genotypes with low pod index (< 20.1) was observed in the Trinitario group (mainly ICS). The Forastero group had the highest percentage of Phytophthora resistant accessions(18.0%). The PA population had the highest proportion of resistant (24.0%) and moderately resistant (38.0%)genotypes. Sixty-five and 99 genotypes were categorised with large bean weight and high bean number, respectively, and 60 genotypes were found with a low pod index. Seventy-eight genotypes were identified with resistance to Phytophthora podrot. A significant relationship was observed between resistance to Phytophthora pod rot (measured as the frequency of localised lesions) and bean number (r = –0.45, p ≤ 0.001)showing that the two traits may complement each other. The combination of low to intermediate pod index with moderate to high resistance to Phytophthora podrot was found in 87 genotypes, 12 of which were also reported to have resistance to witches’ broom disease. These genotypes are of high potential value in cacao breeding and their inclusion in working and corecollections would be justified.

Patterns of Morphological Variation in a Sample of Cacao (Theobroma Cacao L.) Germplasm from the International Cocoa Genebank, Trinidad

The International Cocoa Genebank, Trinidad (ICG,T) contains 2300 accessions representing a broad range of diversity and geographic origins. This study was undertaken to examine the phenotypic relationships in a diverse sample of 600 cacao accessions from the Genebank. The major objectives were to test the applicability of the accepted nomenclature, viz., the definition of classes, as well as to elucidate the relationships between wild and cultivated germplasm and among accession groups. This will facilitate efficient utilisation, management and improvement of cacao genetic resources through the identification of potentially heterotic groups. In addition, information on morphological variation may be considered along with allelic richness or gene frequencies in selecting core collections, and when formulating strategies for future collections in the wild. Considerable phenotypic variation (high coefficients of variation and Shannon Weaver Diversity Index values) in the germplasm studied was found, and the main groups of cacao were clearly separated. Wild cacao was differentiated from cultivated types by all of the quantitative descriptors except pod length. Recognised genetic groups (Trinitario and Forastero) were discriminated by several quantitative traits including sepal length, cotyledon weight, length and width, and pod index. Principal Component Analysis differentiated among 14 accession groups according to geographic origin and genetic grouping. Cotyledon weight, length and number, pedicel column colour, mature pod ridge colour, sepal length, pod basal constriction and surface texture, and ovule number accounted for most of the variation recorded. The observed improvement in the cultivated germplasm, in terms of agronomic traits such as seed weight and pod index, attests to the success of past selection activities. This apparent improvement (particularly among Refractario germplasm) appears to be accompanied by increased style length, a finding that warrants further study. The reduced diversity in sepal length, ligue width, ovule number, and cotyledon length in the cultivated compared to the wild germplasm is consistent with the narrowing of the genetic base in the former. These results have significance for cacao breeding programmes, conservation and future collecting strategies.

Cocoa agronomy, quality, nutritional, and health aspects.

The history of cocoa and chocolate including the birth and the expansion of the chocolate industry was described. Recent developments in the industry and cocoa economy were briefly depicted. An overview of the classification of cacao as well as studies on phenotypic and genetic diversity was presented. Cocoa agronomic practices including traditional and modern propagation techniques were reviewed. Nutrition-related health benefits derived from cocoa consumption were listed and widely reviewed. The specific action of cocoa antioxidants was compared to those of teas and wines. Effects of adding milk to chocolate and chocolate drinks versus bioavailability of cocoa polyphenols were discussed. Finally, flavor, sensory, microbiological, and toxicological aspects of cocoa consumption were presented.

Prediction of Soil Cadmium Bioavailability to Cacao (Theobroma cacao L.) using Single-Step Extraction Procedures

In this study, complexation extractants ammonium bicarbonate diethylene triamine pentaacetic acid (AB-DTPA), diethylene triamine pentaacetic acid (DTPA), and ethylene diamine tetraacetic acid (EDTA) and mild cation-exchange extractants calcium chloride (CaCl2) and ammonium nitrate (NH4NO3) were used to evaluate the bioavailability of soil cadmium (Cd) to cacao in the field. Among the five extractants, the extractable Cd generally followed the order EDTA > DTPA > AB-DTPA > CaCl2 > NH4NO3. Correlation analysis was done between the extractable Cd in soil and total Cd content of cacao tissues (nibs, shells, leaves, and pods). The Cd extracted by CaCl2 and NH4NO3 was significantly (P < 0.05) correlated with some of the tissues but their Pearson correlation coefficients were weak. In contrast, extractants AB-DTPA, DTPA, and EDTA showed stronger, significant correlations to the Cd concentration in all four tissues. Overall, regression analysis demonstrated that AB-DTPA, DTPA, or EDTA can be used to predict bioavailable Cd in soils for cacao. Of these, AB-DTPA and DTPA both showed the strongest correlations compared to EDTA. However, the ease of preparation and the superior shelf-life of DTPA over AB-DPTA make it the preferred reagent for Cd bioavailability extractions from cacao soils and is currently being used to develop cost-effective soil treatments to reduce bioavailable Cd to cacao plants.

Variability of butterfat content in cacao ( Theobroma cacao L.): combination and correlation with other seed-derived traits at the International Cocoa Genebank, Trinidad

Cocoa butterfat and cocoa powder are key economic products from the seeds of the cacao tree (Theobroma cacao L.). In this study, 323 accessions (comprised mainly of Upper Amazon Forasteros and Refractarios) from the International Cocoa Genebank, Trinidad were characterized for one biochemical and five morphological seed-derived traits. The data were analysed using non-parametric statistics including correlation analysis to identify promising parental candidates for future cacao breeding programmes. The Upper Amazon Forastero group had the greatest proportion of accessions with high butterfat content in cotyledons, whereas Refractario and Trinitario groups tended to contain more accessions with high butterfat content per fruit. The correlation of butterfat content of cotyledons with the dry mass of cotyledons was inconsistent in significance and direction. However, consistent significant positive correlations between butterfat content per fruit, cotyledon size and dry mass of cotyledons were found. The results suggested that butterfat content is a likely trait for independent selection but that selection for increased cotyledon size could lead to the selection of genotypes for high butterfat yield. Several promising accessions exhibited favourable levels of multiple traits and MATINA 1/7, CRU 51, AM 2/91 [POU], CRU 133, EET 58 [ECU] and POUND 18/A [POU] could be recommended as good choices for parental stock in breeding programmes for improving cacao butterfat content.

The Effect of Liming on the Availability of Cadmium in Soils and Its Uptake in Cacao (Theobroma c acao L.) In Trinidad & Tobago

ABSTRACT Cadmium (Cd) is absorbed and bio-accumulated by cacao (Theobroma cacao L.) trees, resulting in unacceptably elevated levels in cocoa beans, necessitating measures to reduce its uptake from soils. A field experiment, lasting 18 months, was carried out to assess the effectiveness of liming on pH, bioavailability of Cd in soils and its uptake in cacao tissues. The treatments were: (a) control (untreated) and (b) lime-treated trees. Results demonstrated a significant (P < 0.05) increase in the soil pH (lime treated) and a natural fluctuation in pH for the control. For the lime-treated trees, bioavailable Cd levels generally stabilized with no significant change (P > 0.05) compared to the significant (P < 0.05) increase showed by control trees. The Cd levels in the leaves of both treatments decreased, however, the rate of decline in leaf Cd concentrations for lime-treated trees (−0.1378) was 3x faster than control (−0.0497) trees demonstrating the effectiveness of liming.