Condensed Tannin Accumulation during Seed Coat Development in Five Common Bean Genotypes

Condensed tannins (CT) are important determinants of the colorful seed coats characteristic of many dry bean (Phaseolus vulgaris L.) market classes. These compounds are also important for plant development and human nutrition. Understanding the dynamics of CT accumulation during seed development and the genetic basis of this trait will contribute to the development of more nutritionally beneficial bean cultivars. Differences in patterns of CT accumulation were evaluated in the seed coats of five dry bean genotypes, which had contrasting final CT concentrations. Seed coats were assayed in developing pods taken from 6 d after flowering (DAF) onward to maturity. Condensed tannins were already present at 6 DAF in all genotypes, regardless of their final concentration. Concentrations leveled off and stabilized earlier in low CT genotypes than in those genotypes that ultimately had moderate to high concentrations. In contrast, genotypes that contained moderate to high final CT concentrations accumulated CT throughout seed coat development. Our results indicate that seed coat CT concentration in the seeds harvested during the period from 12 to 18 DAF can serve to accurately predict final CT ranking of seeds.