Philippe Lachenaud

Use of floral descriptors to study variability in wild cocoa trees (Theobroma cacao L.) in French Guiana

Abstract155 clones of wild cocoa trees (Theobroma cacao L.) in French Guiana, belonging to 16 populations identified by surveyors in two different river basins (three sub-basins), along with four international clones used as controls, were characterized with four floral descriptors: petal ligule width, sepal width, gynoecium length and number of ovules per ovary. The data underwent an analysis of variance and a factorial discriminant analysis, and the Mahalanobis distances between the populations were calculated. Significant differences existed between the populations for the four descriptors and the discriminant analysis revealed two main groups among the Guianan cocoa trees. It also isolated them from the controls. The populations in the two basins were not homogeneous, and the sub-basin of origin did not seem to be the main factor structuring the variability of the study populations. There proved to be substantial genotypic variability in the Guianan material for the floral descriptors. Variation within the same family (trees derived from the same pod) was low.

Genetic diversity and population structure in wild stands of cacao trees (Theobroma cacao L.) in French Guiana

The native cacao trees (Theobroma cacao L.) in south-eastern French Guiana represent a noteworthy fraction of the genetic diversity of this species. Several scientific surveys have led to the collection of numerous accessions, which provides an opportunity for investigating the pattern of genetic diversity in natural populations. Using a capillary electrophoresis genotyping system, we fingerprinted 189 wild trees in 18 natural populations. Based on the 15 loci SSR profiles, we analyzed the intra- and inter-population variation and their relationship with control clones. The global allelic richness was 4.87 alleles per locus, but was 2.4 on average within individual populations; gene diversity was 0.368 and observed heterozygosity was low (0.160). Major structuring was discovered in the metapopulation of French Guianan wild cacao trees (Fst = 0.20), which could be explained by the biological characteristics of the cacao tree and the climatic events that affected the Guianan forests in the Quaternary period.RésuméLes cacaoyers spontanés (Theobroma cacao L.) du sud-est de la Guyane française représentent une part notable de la diversité génétique de l’espèce. Plusieurs prospections ont permis la collection de nombreuses accessions, permettant l’étude de la structuration de la diversité dans les populations naturelles. Cent quatre-vingt-neuf cacaoyers spontanés, issus de 18 populations, ont été génotypes grâce à un séquenceur capillaire. Les profils obtenus avec 15 marqueurs SSR ont permis d’analyser les variations intra et inter populations, et leurs relations avec des clones témoins. La richesse allélique globale est de 4,87 allèles par locus, mais de 2,4 en moyenne dans les populations; la diversité génique est de 0,368 et l’hétérozygotie observée est faible (0,160). Une importante structuration existe dans la metapopulation de cacaoyers spontanés Guyanais, avec un Fst de 0,20, qui pourrait s’expliquer par les caractéristiques biologiques du cacaoyer et les événements climatiques ayant affecté les forêts guyanaises au Quaternaire.

Bean quality traits and sensory evaluation of wild Guianan cocoa populations (Theobroma cacao L.)

Naturalized cocoa populations originating from the Oyapok and Tanpok basins in French Guiana were studied for their technological characters (bean count, fat content, purine content) and sensory characters (overall aroma intensity, cocoa flavour, acidity, bitterness, astringency, fruity or floral tastes, aftertaste, etc.), along with three controls (Amelonado and Ecuadorian varieties). The bean count in Guianan cocoa was higher than that of the controls, but it generally remained acceptable (below 100). Caffeine content was much higher than that of the Amelonado control. The overall aroma intensity and cocoa flavour of the chocolates made with the dry cocoa beans from Guianan trees were statistically superior to those of the industrial reference, the West African Amelonado. The other criteria studied, particularly the fat content, did not reveal any significant differences from the controls.

Fruit trait variability in wild cocoa trees (Theobroma cacao L.) from the Camopi and Tanpok basins in French Guiana

Abstract Under conditions at Paracou—Combi (Sinnamary, French Guiana), pods from 76 ortets of local wild cocoa trees, belonging to nine populations from the Camopi and Tanpok river basins, were characterized ex situ. For each ortet, at least 35 pods from the main crop were characterized (2,690 pods). The seven primary traits studied were: pod length, maximum pod diameter, total weight of one pod, wet bean weight, wartiness, apex shape and basal constriction. Variability was large and differences between populations were generally significant. A discriminant analysis confirmed the existence of two morpho—geographic groups: one with large warty pods, the other with smaller, smoother and round pods. Indications are given to breeders for selection among these clones.

Le remplissage des cabosses des cacaoyers spontanés de Guyane (Theobroma cacao L.)

Abstract Under conditions at Paracou-Combi (Sinnamary, French Guiana), 77 ortets of local wild cocoa trees, belonging to nine populations from the Camopi and Tanpok river basins, were characterized for their average number of normal beans per pod, and their apparent fertility (ratio of the average number of normal beans per pod to the average number of ovules per ovary). The comparison with the Upper-Amazon Forastero clone NA 32 and various local Amelonado and Trinitario clones revealed general susceptibility among the Guianan wild cocoa trees to incomplete pod filling. For the set of Guianan clones, the average number of normal beans per pod was low (25.3), the coefficient of variation for the number of normal beans per pod was high (43%) and apparent fertility was low (0.57). Poor pod filling was not correlated to their compatibility rate.

The Guiana cacao genetic group (Theobroma cacao L.): a new core collection in French Guiana

Abstract Since 1985, CIRAD has been involved in surveying, collecting, studying and conserving ex situ wild cacao trees of French Guiana. Around 225 accessions of this genetic material (open progenies and clones), derived from 18 demes (sub-populations), are currently conserved in a collection at the Perennial Plants Biological Resource Centre (CRB-PPG) in French Guiana, at CIRAD’s Paracou-Combi station, in Sinnamary. In 2004, an initial “core collection” of clones was founded on a virtually exhaustive representation of the different demes collected, with some phenotypically well-described clones. Following the genotyping of 181 of those clones by GBS (Genotyping by Sequencing), the availability of a large number of SNP markers (Single Nucleotide Polymorphism) enabled us to modernize the “core collection”. Thus, of the 181 wild cacao trees clones, genotyped by 1953 SNPs (without missing data), a new core collection was obtained using COREFINDER software, comprising 41 clones representing 100% of the variability encountered.

The Criollo cacao tree (Theobroma cacao L.): a review

In commercial terms, Criollo cacao trees (Theobroma cacao L.) are reputed to be the source of the commercial product (fermented and dried cocoa beans), which sells for the best price on the market. Nevertheless, the term “Criollo” has numerous meanings and interpretations depending on if it is used by commercial users or botanists, growers or breeders. Our review aims to specify which cocoas can justifiably carry the Criollo name. “Criollo” is a botanical subspecies of Theobroma cacao, i.e. Theobroma cacao subsp. cacao; however, the true Criollos form just one of the ten currently accepted genetic groups in the species. We thus provide an overview of genetic studies on the subject (published or not), along with what is currently known about “True Criollo” or “Ancient Criollo” cacao trees. In fact, there are few representatives in collections that are duly acknowledged to be true Criollos, particularly in the two International Cocoa Genebanks, where only seven clones are available. It is nonetheless certain that some true Criollos do exist in other collections but have not been formally identified (by genetic studies) as members of the Criollo genetic group. Likewise, some true Criollos, be they cultivated or subspontaneous, exist in Mexico and Central and South America (Venezuela and Colombia). However, certain clones called “modern Criollos”, which are closely related to the true Criollos but arise from hybridization with other genetic groups, are more common.