Variation in the mating system of Bixa orellana L. (achiote) under three different agronomic systems

•Mating system (MS) varied between two phenotypes and among three agronomic systems.•A mixed MS in backyards and an outcrossing MS in mono- and poly-culture were found.•Maternal inbreeding coefficient varied from 0.18 to 0.49 (higher values in backyard).•Excepting the pink phenotype from polyculture, biparental inbreeding was ≈0.3.•Siring of seeds varied from 3 to 7, except the pink phenotype in polyculture (≈30).

Bixa orellana L. (achiote), is a tropical species that produces high amounts of bixin, used as a commercial food pigment. In Yucatan, B. orellana (achiote) is cultivated under three different agronomic systems: backyard (solar), polyculture (milpa), and monoculture. Two promising phenotypes affecting bixin production have been identified. The phenotypes differ in flower and fruit colour, fruit dehiscence and bixin contents. Reflecting differences in plant density, species diversity and management factors among agronomic systems and differences in flowering synchrony between phenotypes, mating system parameters might vary, such as outcrossing rates (tm and ts), biparental inbreeding (tm-ts;rpm- rps), the fixation index of maternal plants (F) and paternity correlation (rpm). To compare such parameters between different B. orellana phenotypes among agronomic systems, 10 offspring from 20 genetic families of B. orellana per agronomic system were amplified using sequence-related amplified polymorphism (SRAP) molecular markers. MLTR software was used assuming a mixed mating system. Plants sown in backyard showed a mixed mating system, while in poly- and monoculture, they showed predominantly an outcrossing system; biparental inbreeding was similar in backyard, poly- and monoculture; the maternal inbreeding coefficient was higher in backyards than in poly- and monoculture; and plants in backyards and monoculture are less promiscuous than plants in polyculture. Variations between phenotypes within each agronomic system were also recorded. B. orellana displays a mixed mating system affected by the agronomic system. Thus, the selection of offspring should consider variation in the mating system in the design of alternative breeding improvement programs.