Morphoanatomical characteristics of fruits in Bixa orellana L. accessions with contrasting dehiscence phenotypes

The main source of bixin is the Bixa orellana L. plant, known as achiote. Bixin, a red apocarotenoid, accumulated mainly in the seeds. The major genetic improvement goal in B. orellana plants is to increase their bixin content. In the search for the most relevant trait associated with bixin production, one of the significant features was the fruit's dehiscence. To generate insight into this characteristic, three variants of B. orellana were selected with different fruit phenotypes related to the dehiscent phenomenon level (dehiscent, indehiscent, and partially dehiscent) and bixin content. Detailed analysis of the anatomical structures of the fruits reveals differences in the dehiscence zone, which is important for seed release, the endocarp glands and vascular bundles vary widely between the three phenotypes. The distribution and number of the endocarp gland vary according to dehiscent phenomena. The dehiscent fruits have smaller cells and a well-defined dehiscence zone with enzymatic degradation. The partially dehiscent fruits combine characteristics of both fruit of the other phenotypes. Lignin deposition was accessed through phloroglucinol-HCl and autofluorescence. Dehiscent fruits showed low lignin deposition, while indehiscent fruits exhibited a clear lignin accumulation in several structures but not in the dehiscence zone. Partially dehiscent fruits showed an intermediate pattern that reinforces their dehiscent or non-dehiscent character. This detailed analysis shows how lignification patterns are associated with each fruit phenotype’s functionality and opening capacity. Lignification and dehiscent phenomena may be important traits in characterizing the B. orellana variants.