Physiological effects of seed coat darkening in Cowpea bean (Vigna unguiculata L. Walp): aging and water uptake.

José Oscar L. de Oliveira, Jr^1,2, Alfredo A. C. Alves^2,3, Christina Walters²

¹Embrapa Mid-North, Teresina, PI, Brazil

²USDA-ARS National Center for Genetic Resources Preservation, Fort Collins, CO

³Embrapa LABEX-USA, Fort Collins, CO

Cowpea bean (Vigna unguiculata L. Walp) is an important annual food crop in Northeast Brazil. Dry storage of these seeds leads to a slow and uneven darkening of the seed coat.  The mixture of seed colors creates an unacceptable product for consumers. The aim of this study was to determine the kinetics of seed color change and the physiological consequences to seed quality.   The study used two cowpea bean cultivars, BRS Rouxinol and BRS Pujante that were released by Embrapa for Northeast Brazil.  Differences in seed quality were assessed for water permeability and sensitivity to high moisture aging stress. Seeds were separated in two color classes -light and dark – and then assessed for water uptake and response to 75% RH and 45^oC conditions for up to 11 days. Water uptake was measured by placing individual seeds in a vial containing 1.5 ml of water and measuring fresh mass every 10 minutes. Seeds viability was tested using a standard germination assay. Lighter colored seeds imbibed water significantly slower than darker seeds, suggesting that seeds with light colored seed coats are hard-seeded. There were no measured differences among light and dark seeds following the brief high humidity and temperature treatment. Future work will investigate chemical changes to seed coats resulting in color change and investigate responses to longer high humidity exposure.