Cacao domestication II: progenitor germplasm of the Trinitario cacao cultivar

Cacao (Theobroma cacao L.) has been cultivated in Central America since pre-Columbian times. The type of cacao cultivated in this region was called Criollo; cacao populations from the Amazon basin were called Forastero. The type of Forastero most commonly cultivated until 1950 was named Amelonado. Historical data show Trinitario cacao to have originated in Trinidad, resulting from natural hybridisation between Criollo and Amelonado Forastero. Doubts persist on the source of the Amelonado Forastero involved in the origin of Trinitario; the Amelonado parent may have come from the Lower Amazon, the Orinoco or the Guyanas. Most of the cacao cultivated worldwide until 1950 consisted of Criollo, Trinitario and Amelonado. From the early 1950s, Forastero material collected in the Upper Amazon region during the 1930s and 1940s began to be employed in breeding programmes. To gain a better understanding of the origin and the genetic basis of the cacao cultivars exploited before the utilisation of germplasm collected in the Upper Amazon, a study was carried out using restriction fragment length polymorphism and microsatellite markers. Trinitario samples from 17 countries were analysed. With molecular markers, it was possible to clearly identify three main genotypes (represented by clones SP1, MAT1-6 and SIAL70) implicated in the origin of most Trinitario clones.

Cacao domestication II: progenitor germplasm of the Trinitario cacao cultivar.

Cacao (Theobroma cacao L.) has been cultivated in Central America since pre-Columbian times. The type of cacao cultivated in this region was called Criollo; cacao populations from the Amazon basin were called Forastero. The type of Forastero most commonly cultivated until 1950 was named Amelonado. Historical data show Trinitario cacao to have originated in Trinidad, resulting from natural hybridisation between Criollo and Amelonado Forastero. Doubts persist on the source of the Amelonado Forastero involved in the origin of Trinitario; the Amelonado parent may have come from the Lower Amazon, the Orinoco or the Guyanas. Most of the cacao cultivated worldwide until 1950 consisted of Criollo, Trinitario and Amelonado. From the early 1950s, Forastero material collected in the Upper Amazon region during the 1930s and 1940s began to be employed in breeding programmes. To gain a better understanding of the origin and the genetic basis of the cacao cultivars exploited before the utilisation of germplasm collected in the Upper Amazon, a study was carried out using restriction fragment length polymorphism and microsatellite markers. Trinitario samples from 17 countries were analysed. With molecular markers, it was possible to clearly identify three main genotypes (represented by clones SP1, MAT1-6 and SIAL70) implicated in the origin of most Trinitario clones.

Cacao domestication I: the origin of the cacao cultivated by the Mayas.

Criollo cacao (Theobroma cacao ssp. cacao) was cultivated by the Mayas over 1500 years ago. It has been suggested that Criollo cacao originated in Central America and that it evolved independently from the cacao populations in the Amazon basin. Cacao populations from the Amazon basin are included in the second morphogeographic group: Forastero, and assigned to T. cacao ssp. sphaerocarpum. To gain further insight into the origin and genetic basis of Criollo cacao from Central America, RFLP and microsatellite analyses were performed on a sample that avoided mixing pure Criollo individuals with individuals classified as Criollo but which might have been introgressed with Forastero genes. We distinguished these two types of individuals as Ancient and Modern Criollo. In contrast to previous studies, Ancient Criollo individuals formerly classified as 'wild', were found to form a closely related group together with Ancient Criollo individuals from South America. The Ancient Criollo trees were also closer to Colombian-Ecuadorian Forastero individuals than these Colombian-Ecuadorian trees were to other South American Forastero individuals. RFLP and microsatellite analyses revealed a high level of homozygosity and significantly low genetic diversity within the Ancient Criollo group. The results suggest that the Ancient Criollo individuals represent the original Criollo group. The results also implies that this group does not represent a separate subspecies and that it probably originated from a few individuals in South America that may have been spread by man within Central America.

Genetic diversity among wild and cultivated populations of Hevea brasiliensis assessed by nuclear RFLP analysis.

Restriction fragment length polymorphism was assessed in wild and cultivated populations of Hevea brasiliensis using random probes from an Hevea nuclear library. One-hundred-and-sixty-four individuals were surveyed, and the results discussed in the light of previous work performed on isozyme variation. Both studies show that germplasm collections have led to an effective enrichment of the genetic resources available for Hevea breeding, and that cultivated clones have conserved a relatively high level of polymorphism, despite their narrow genetic base and their high level of inbreeding. An equivalent level of polymorphism is revealed by random nuclear probes and isozymes. However, the genetic structuring of the diversity appears more striking using RFLP markers. Wild accessions can be divided into three genetic groups according to their geographical origin. The present results are an essential guide to the incorporation of wild material in breeding schemes.

Ribosomal DNA variations in wild and cultivated rubber tree (Hevea brasiliensis).

Ribosomal DNA variations were surveyed to assess the genetic variability among Hevea brasiliensis genetic resources. One hundred and sixty-eight individuals, including 73 cultivated Wickham clones and 95 wild clones from a prospection, were analyzed. Restriction mapping of rDNA units showed that RFLP variations are the result of both length and site (EcoRI) variations in the intergenic spacer (IGS). These variations can be revealed between as well as within individuals. A total of 12 spacer length variants is scored in the whole population, as well as two different ribosomal units (refered as type I and type II), defined by the presence or absence of an EcoRI site. Particular associations between spacer length variants and unit types can be revealed, leading to complex RFLP patterns. Cultivated clones appear to be less variable than prospections but show, however, a relatively high level of variability despite their narrow genetic base. Furthermore, IGS variations allowed a structuring within wild clones to be drawn, based mainly on their geographical origin. Some interesting discrepancies with previous work on isozyme variations are discussed and show the interest of surveying different genetic markers for diversity studies.