Ecophysiology of the cacao tree (original) (raw)
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Cacao breeding in Colombia, past, present and future
Breeding Science
Cacao (Theobroma cacao L.) is considered a key crop in Colombian social programs aiming at alleviating rural poverty, promoting peace in post-conflict regions and, replacing crops used for illicit purposes. Colombia is thought to be part of the center of origin of cacao; several germplasm collecting expeditions have been implemented, dating back to the 1940s. Despite that history, the first breeding program based on creating, selecting, and releasing full-sib progenies made extensive use of accessions introduced from other countries as parents. A new breeding strategy was adopted in the 1990s, based on mass selection of promising trees (high-yield and disease-resistant) in farmers' fields, resulting in the selection of clones released to farmers as planting material. In 2012, a new strategy, Recurrent Selection, was adopted by the Colombian Corporation for Agricultural Research, Agrosavia, based on the development of improved populations and allowing the selection of clones at the end of each cycle of recombination. The use of molecular markers is being integrated into this program in order to assist breeders in selecting material. This review provides details about the history and perspectives of the cacao breeding program in Colombia.
Upper Amazon Forastero (UAF) cacao clones account for approximately 60% of cacao cultivation globally, and are widely used in breeding. This study was undertaken at the International Cocoa Genebank, Trinidad to examine the phenotypic relationships among several UAF accession groups, viz., Iquitos Mixed Calabacillo (IMC), Morona (MO), Nanay (NA), Parinari (PA) and Scavina (SCA) and some of their known progenitors, POUND accessions using Cluster Analysis (CA) and Principal Component Analysis (PCA). Some of the IMC, NA and SCA clones clustered with their putative mother trees. The grouping of the IMC clones in a few almost homogeneous clusters suggested that this group was the least diverse phenotypically. More diversity was expressed within the POUND, MO, NA, PA, and SCA groups. The considerable phenotypic diversity in the SCA and MO groups, expressed for traits such as pod index, cotyledon weight and width and pod apex form, seems not to be explained by a single mother tree source for each group. Significant phenotypic diversity in this UAF germplasm sample, measured by the Shannon Weaver Diversity Index (values 0.5) and coefficients of variation (>10%), was observed for some of the traits studied including stamen filament pigmentation, pod apex form, pod index, cotyledon weight and style length. IMC 3 and 63 were among the most phenotypically distinct accessions based on the results of CA and PCA. These results, in conjunction with those from genetic diversity studies, should prove useful for future cacao breeding programmes and will facilitate the formulation of strategies to effectively manage cacao genetic resources -select core and working collections and plan future collections in the wild to increase the genetic diversity of cacao conserved ex situ.
Ecophysiology of the cacao tree BJPP 2007
Cacao, one of the world's most important perennial crops, is almost exclusively explored for chocolate manufacturing. Most cacao varieties belong to three groups: Criollo, Forastero and Trinitario that vary according to morphology, genetic and geographical origins. It is cropped under the shade of forest trees or as a monocrop without shade. Seedlings initially show an orthotropic growth with leaf emission relatively independent of climate. The maturity phase begins with the emission of plagiotropic branches that form the tree crown. At this stage environmental factors exert a large influence on plant development. Growth and development of cacao are highly dependent on temperature, which mainly affects vegetative growth, flowering and fruit development. Soil flooding decreases leaf area, stomatal conductance and photosynthetic rates in addition to inducing formation of lenticels and adventitious roots. For most genotypes drought resistance is associated with osmotic adjustment. Cacao produces caulescent flowers, which begin dehiscing in late afternoon and are completely open at the beginning of the following morning releasing pollen to a receptive stigma. Non pollinated flowers abscise 24-36 h after anthesis. The percentage of flowers setting pods is in the range 0.5-5%. The most important parameters determinants of yield are related to: (i) light interception, photosynthesis and capacity of photoassimilate distribution, (ii) maintenance respiration and (iii) pod morphology and seed fermentation, events that can be modified by abiotic factors. Cacao is a shade tolerant species, in which appropriate shading leads to relatively high photosynthetic rates, growth and seed yield. However, heavy shade reduces seed yield and increases incidence of diseases; in fact, cacao yields and light interception are tightly related when nutrient availability is not limiting. High production of non-shaded cacao requires high inputs in protection and nutrition of the crop. Annual radiation and rainfall during the dry season explains 70% of the variations in annual seed yields.
Variation and its distribution in wild cacao populations from the Brazilian Amazon
Brazilian Archives of Biology and Technology, 2003
A sample of 64 progenies (320 cacao trees as a whole) from four Brazilian Amazon basins was collected and evaluated on the basis of 15 fruit and seed traits. Nested univariate analyses of variance showed significant variation across progenies and basins. However, most of the variability appeared to be due to among trees and basins differences. The multivariate analysis showed that the differentiation in cacao populations occurred among basins. Since cacao diversity was predominantly found in trees within basins and among basins, one should optimize the collecting process by taking as many trees as possible starting from few progenies and many river basins. These findings seemed to validate gene conservation efforts made to date to preserve the cacao genetic resources and provide insight into the cacao genetic structure aiming cacao collection, management and improvement.
Cacao breeding in Bahia, Brazil: strategies and results
Crop Breeding and Applied Biotechnology, 2011
Cacao was introduced in Bahia in 1756, becoming later the largest producer state in the country. In order to support the planting of cacao in the region, a breeding program was established by CEPEC at the beginning of the 1970s. For a long time, the program consisted in testing new hybrids (full-sibs) and releasing a mixture of the best ones to farmers. Lately, particularly after the witches´ broom arrival in the region, in 1989, recurrent breeding strategies were implemented, aiming mainly the development of clones. From 1993 to 2010, more than 500 progenies, accumulating 30 thousand trees, were developed by crossing many parents with resistance to witches´ broom, high yield and other traits. In this period, more than 500 clones were put in trials and 39 clones and 3 hybrids were released to farmers. In this paper the strategies and results achieved by the program are reviewed. Overall the program has good interface with pathology and genomic programs.
Genetic Resources and Crop Evolution, 2019
Cacao (Theobroma cacao L.) accessions conserved at the International Cocoa Genebank Trinidad (ICGT) are routinely characterised and evaluated in terms of traits of taxonomic and economic interest. The resulting data are crucial for selecting suitable candidates for future germplasm utilisation and breeding. In this study, the distribution of traits of taxonomic and economic interest was examined among Trinitario accession groups, represented by 260 accessions, and compared to what pertains for the 1900 genotypes characterised at the ICGT. Among the 1900 accessions studied, the Pod Index, an indicator of yield potential, ranged from 13.9 to 92.8. Twentythree percent of the accessions with superior yield potential (Pod Index of 21 or lower) were 'Trinitarios', including the best. Despite a significantly negative correlation (r =-0.162, P \ 0.0001) between seed mass and seed number of the accessions studied, several Trinitarios combined large seed number (44 or more) with large seed (cotyledon) mass (1.2 g or more). The Trinitarios selected in Trinidad were observed to be phenotypically closely related. Trinitarios with high yield potential, large seed size and other favourable traits were identified. They are potentially useful sources of genes for introgression into Trinitario planting material in fine or flavour cocoa producing countries, which provide premium cocoa to an ever expanding global niche market. The resulting economic and social benefits of improvement in Trinitario cacao planting material should be significant.
Morphological characterization of elite cacao trees (Theobroma cacao L.) in Tumaco, Nariño, Colombia
Revista Colombiana de Ciencias Hortícolas, 2016
The cacao has become an essential part of the fight against the effects of illegal crops and rural poverty in Colombia. Because of their bromatological characteristics, cocoa beans are preferred in markets. However, there are few studies on the variability of the regional genotypes. The goal of this study was to characterize the cacao trees in Tumaco, Nariño (Colombia) and establish their morpho-agronomic variability. Plant collections were conducted in five production zones of the municipality between 0 to 270 m. On each farm, the productivity and plant health variables were recorded for the outstanding plants. The characterization was carried out using a Principal Component Analysis (PCA), Multiple Correspondence Analysis (MCA) and Cluster analysis. In the PCA, the first five components explained 70.2% of the variation. The first three components were characterized by productivity, while the last two components showed a low pod and grain index. In the MCA, the first three factors ...