PS 39-77 - Genetic diversity of Theobroma cacao in small and local farms in Latin America and the Caribbean Islands

Abstract: Theobroma cacao (Chocolate) likely originated in the Amazon Basin and became widespread throughout Latin America at least 5,000 years prior to European contact in the 16^th century. Today, 85% of cacao produced commercially comes from outside this region. Globally, nearly half of all cacao produced succumbs to diseases, predominately fungal pathogens. Widespread commercial cultivars are especially vulnerable to pathogens due to their low genetic diversity. Small farms using traditional agricultural practices are a potential reservoir of genetic diversity for cacao. Because cacao is an obligate outcrosser and can interbreed with wild crop relatives, traditional cultivation methods that involve growing cacao in close proximity to wild Theobroma spp. should help maintain higher genetic diversity. However, local farmers, like industrial farms, may inbreed their successful cacao crops to maintain the quality of their yield. We hypothesized that cacao would be more diverse on small farms in Latin America and the Caribbean islands than on large-scale commercial farms that have undergone genetic bottlenecks. We performed a systematic literature review of small and local farms in this region to determine the extent of crop inbreeding on these farms. Our search terms were “genetic diversity” AND “Indigenous” AND “cacao” AND “farm” OR “garden” –“pathogen,” and included papers that specified collecting leaf tissue from small and Indigenous farms in Latin America and the Caribbean Islands. Of the 10 farms included in our review and meta-analysis, 9 showed evidence of inbreeding. Notably, the inbreeding on these farms is similar to or greater than levels of inbreeding on commercial farms, raising concerns about whether these small farms are truly a source of genetic diversity for cacao. Concerningly, of the 24 countries that produce cacao in our study region, we only found studies from 10 countries, despite broadening our scope to include all small-scale farms, not just those using traditional Indigenous farming methods. Thus, there is a crucial need for further genetic diversity research on farms using traditional agriculture practices. Furthermore, use of the morphological classifications Trinitario, Forastero, and Criollo is still prevalent in cacao research, despite these categories lacking a genetic basis. A shift to genetically founded classifications is necessary for accurate identification of reservoirs of genetic diversity for cacao.