Mass Selection of Drought Tolerant Cacao in Bahia, Brazil: Morphological, Genetic Structure, and Diversity Analysis

Drought events in cacao production regions worldwide are causing plant mortality, decreasing productivity, and reduction in income for cacao farmers. Therefore, the selection and delivery of drought-tolerant cacao (DTC) plants for farmers to mitigate the negative effects of drought is particularly important. The objectives of this study were to register the use of mass selection to collect DTC plants from farmers' fields, describe the morphological aspects of 96 genotypes, and analyze genetic diversity using single nucleotide polymorphism (SNP) markers. A hundred and eight plants were selected and collected from farmers' fields in two regions of the state of Bahia, Brazil, where the plants have been strongly affected by droughts. We described the morphological features of the plants collected and used 143 polymorphic SNP markers for genotyping. The results have shown that DTC candidate plants can be collected by mass selection in the field. The plants collected had variations in fruit and plant vigor, and reactions in response to drought. We found DTC candidate plants with green and red fruits, indicating the presence of germplasm from the two main cacao groups (Criollo and Forastero). Bayesian and multivariate analysis have shown the presence of genetic structure and diversity among the germplasm collected. The plants were separated into six main groups: Amelonado (34 genotypes), Iquitos (2), Contamana-Iquitos mixed (7), Amelonado-Iquitos mixed (16), Amelonado-Contamana mixed (26), and Amelonado-Contamana-Iquitos mixed (11). Evidence of genetic diversity was supported by descriptive statistics (H-e, I, F). The Amelonado genotypes, as expected, had the lowest diversity because they are a homogeneous population. DTC genotypes have morphological and molecular genetic diversity that can be used for the selection of agronomically superior rootstocks for drought tolerance, as well as for breeding programs.