Preliminary studies toward genetic improvement of annatto (Bixa orellana L.)

Annatto (Bixa orellana L.) is a native species of the Neotropics. It is commercially grown for the high apocarotenoid pigment content in its seed coat, particularly bixin (BXN) (9′Z-6,6′-diapocarotene-6,6′-dioate). Bixin is a natural orange-red pigment used primarily as a coloring agent in dairy products, baked goods, vegetable oils, and drinks. Large-scale propagation of annatto is problematic because it is cross-pollinated, highly heterozygous, and has heterogeneous bixin content. Another drawback is dehiscence in dry capsules in high bixin content varieties. Previous research on B. orellana does not address the biochemical or molecular aspects of apocarotenoid content or procedures for artificial pollination of Mexican variants. In an initial effort toward genetic improvement, preliminary studies were done to begin developing procedures for artificial pollination of annatto, understand its reproductive biology, and investigate the bixin and carotenoid content in the seeds of variants selected based on flower and fruit morphological traits. In the state of Yucatan, Mexico; annatto begins flowering in September, but the optimum period for artificial pollination and fruit set is October and November. Under natural conditions an average of 32 ± 5.3 seeds per fruit are produced. Pistil receptivity lasts approximately 4 h and peaks between 08:00 and 12:00 h. Based on in vitro germination, average pollen viability is about 86%, and pollen longevity declines by about 50% 24 h after release from anther. Significant differences in carotenoids and bixin contents in mature seeds were observed between the studied annatto variants. The pink flower variant had the highest contents of both pigments, and one of the white flower variants (‘peruana verde’) had the lowest.