Genetic Diversity and Structure of Bixa orellana var. urucurana, the Wild Ancestor of Annatto, in Brazilian Amazonia

The genus Bixa belongs to the Bixaceae family and includes five species (B. orellana, B. arborea, B. excelsa, B. platycarpa and B. urucurana). A recent analysis suggests that B. urucurana is the wild ancestor of cultivated annatto (B. orellana), and should be considered a variety of this species. This variety occurs in open forests or anthropogenic landscapes, although never cultivated, and is always associated with riparian environments. The aim of this study was to evaluate the genetic diversity and structure of Bixa orellana var. urucurana in Brazilian Amazonia. We evaluated 170 accessions from 10 municipalities in the states of Rondônia, Pará and Roraima in Brazil, using 16 microsatellite loci developed for annatto. A total of 194 alleles was observed, with an average of 12.12 alleles per locus. Higher levels of expected (H_E) than observed (H_O) heterozygosities for all populations were found. Bayesian analysis, Neighbor-Joining dendrograms and PCAs suggest the existence of three structured groups among the accessions. F-statistics (F_IS = 0.360; F_ST = 0.201; F_IT = 0.489) also confirmed high levels of genetic structure. Low levels of gene flow among populations (N_m = 0.545) were observed. A strong and positive correlation between genetic and geographic distance (r = 0.860, P = 0.003) was found, suggesting that genetic differentiation might be caused by geographic isolation due to distance. These results will provide information to understand domestication and dispersal of annatto in Amazonia.

Financial support: FAPESP and CNPq