Grafting typically offers a shortcut to breed tree orchards throughout a multidimensional space of traits. Despite an overwhelming spectrum of rootstock-mediated effects on scion traits observed across several species, the exact nature and mechanisms underlying the rootstock-mediated effects on scion traits in cacao (Theobroma cacaoL.) plants often remain overlooked. Therefore, we aimed to explicitly quantify rootstock-mediated genetic contributions in recombinant juvenile cacao plants across target traits, specifically cadmium (Cd) uptake, and its correlation with growth and physiological traits. Content of chloroplast pigments, fluorescence of chlorophylla, leaf gas exchange, nutrient uptake, and plant biomass were examined across ungrafted saplings and target rootstock × scion combinations in soils with contrasting levels of Cd. This panel considered a total of 320 progenies from open-pollinated half-sib families and reciprocal full-sib progenies (derived from controlled crosses between the reference genotypes IMC67 and PA121). Both family types were used as rootstocks in grafts with two commercial clones (ICS95 and CCN51) commonly grown in Colombia. A pedigree-based best linear unbiased prediction (A-BLUP) mixed model was implemented to quantify rootstock-mediated narrow-sense heritability (h²) for target traits. A Cd effect measured on rootstocks before grafting was observed in plant biomass, nutrient uptake, and content of chloroplast pigments. After grafting, damage to the Photosystem II (PSII) was also evident in some rootstock × scion combinations. Differences in the specific combining ability for Cd uptake were mostly detected in ungrafted rootstocks, or 2 months after grafting with the clonal CCN51 scion. Moderate rootstock effects (h²> 0.1) were detected before grafting for five growth traits, four nutrient uptake properties, and chlorophylls and carotenoids content (h²= 0.19, 95% CI 0.05–0.61,r= 0.7). Such rootstock effects faded (h²< 0.1) when rootstock genotypes were examined in soils without Cd, or 4 months after grafting. These results suggest a pervasive genetic conflict between the rootstock and the scion genotypes, involving the triple rootstock × scion × soil interaction when it refers to Cd and nutrient uptake, early growth, and photosynthetic process in juvenile cacao plants. Overall, deepening on these findings will harness early breeding schemes of cacao rootstock genotypes compatible with commercial clonal scions and adapted to soils enriched with toxic levels of Cd.

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.

The objective of this study was to determine Cd accumulation under water-deficit conditions by young cacao plants. The study was conducted under greenhouse conditions. Two full-sib families (IMC67 × PA121 and SCA6 × PA121), obtained through controlled crosses, and an open pollinated half-sib seedling family of IMC67, widely used as rootstock in Colombia, were employed. Plants were grown in Cd-contaminated soil (0.356 mg kg⁻¹) without external sources of the metal. They were subjected to water deficit by suspending irrigation for consecutive periods of 19 and 27 days (D19 and D27), followed by rehydration. Water stress reduced leaf water potential (Ψ_leaf) with values from −1.51 to −2.09 MPa, with full-sib family SCA6 × PA121 being the most tolerant to water deficit. Cd concentration was influenced by biomass reduction (observed in IMC67 × PA121 and SCA6 × PA121) and transpiration rate (evident in IMC67) caused by water deficit. Full-sib progenies IMC67 × PA121 and SCA6 × PA121 accumulated more Cd in the plants than open pollinated IMC67, with higher Cd accumulation in leaves. The translocation factor (TF) revealed that the aboveground organs of the progenies were enriched with Cd (TF > 4). Water deficit increased Cd translocation from roots to leaves in IMC67 × PA121 and IMC 67, while there were no significant changes in SCA6 × PA121. Full-sib family SCA6 × PA121 stood out as the most promising progenies due to their water-stress tolerance and Cd accumulation stability. This study introduces a discussion about the influence of water stress on Cd accumulation in Theobroma cacao.

Did you know that chocolate is obtained from beans extracted from the fruit of a tree called Theobroma cacao? The fruits are yellow or deep red pods that contain beans covered with a sweet-bitter pulp. Cacao originated in the Amazon region and, for this reason, South America has the highest genetic diversity of the species. The special flavor of each chocolate depends on genetics and the process of transforming cacao seeds into chocolate bars. Cacao cultivation has a fascinating story for which we have to travel through time. The story begins way back with ancient indigenous civilizations that consumed cacao as a drink, and for whom cacao beans were a symbol of power. After the Spanish colonization of the Americas, cacao pods were taken to Europe. In this article, we will learn about the history and importance of cacao for some civilizations, the genetic diversity of cacao species, and the transformation of cacao beans to chocolate.