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Title: Seed coat darkening in Cowpea bean

Author
item DE OLIVEIRA JR., JOSE OSCAR - Embrapa-Labex
item ALVES, ALFREDO - Embrapa-Labex
item Walters, Christina

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 11/4/2011
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Seed coat of cowpea bean (Vigna unguiculata L. Walp) slowly browns to a darker color during storage. High temperature and humidity during storage might contribute to this color change. Variation in browning rate among seeds in a lot leads to a mixture of seed colors creating 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. Seeds of 6 cowpea cultivars, ‘BRS Gurguéia’, ‘BRS Marataoã’, ‘BRS Rouxinol’, ‘BRS Pujante’, ‘BRS Pajeu’, and ‘BRS Pingo de Ouro 1-2’, were examined for variation in tendency for coat color to change during storage. Two additional cultivars, ‘BRS Gauriba’ and ‘BRS Xiquexique’ have white seed coats that do not change colors, and these were used as negative controls. Seed lots were harvested between 2008 and 2011from different locations to give a mulitfactorial experimental design. Seeds coat color classes were measured by computer software and seeds within lots were divided into subsets based on lightness and darkness. Individual seeds from each subset were assessed for water permeability by measuring fresh mass every 10 minutes after placing the dry seed in a vial containing 1.5 ml of water. Scarification treatments were used to confirm seed coat impermeability to water. Seeds were scarified by placing them in an air pressured mill and mixed for 1 or 2 minutes. Resistance of seed lots to deterioration under warm, humid conditions was assessed by viability losses in seeds stored at 75% RH and 45C conditions for up to two months. Relative humidity was controlled using saturated solutions of NaCl (75% RH). Germination was measured in scarified and unscarified seeds that had been rolled in wet paper towels and incubated for 11 days at 25C. Percent of normal and abnormal seedlings and radicle length was measured. Lighter colored seeds imbibed water significantly slower than darker seeds, but there were no measured differences in response to warm, humid conditions among light and dark seeds. Future work will investigate chemical changes to seed coats associated with the color change and responses to longer high humidity treatments. Knowledge gained from these experiments can lead to improve seeds quality and commercial marketability of seeds. The project implements a new partnership between USDA/ARS/NCGRP/PGPRU, Feira de Santana State University and Piaui Federal University.