The importance of genetically determined seed coat characteristics to seed quality in grain legumes

Comparisons of five pairs of isogenk lines of peas, differing only in the A gene for seed coat colour showed that white seeds (genotype aa) imbibed more rapidly than coloured seeds (AA), suffered greater imbibition damage revealed by dead tissue on the cotyledons, and higher solute leakage. Seed-coat pigmentation was closely associated with slow water uptake, since when expression of the A gene was suppressed by the recessive pollens gene, the resulting white seeds {palpal AA) imbibed rapidly. The slow water uptake by coloured seeds was not due to the restriction of water entry by the seed coat since the differences in imbibition rate were maintained when a portion of the seed coat was removed and seeds were imbibed with the exposed cotyledon in contact with moist filter paper. Imbibition of similarly treated seeds by immersion in polyethylene glycol solutions (1–4%) which increased the seed/solution wettability, had little effect on the water uptake of coloured seeds compared to imbibition in water whereas that of white seeds increased in the first 10 mins imbibition. Poor wettability of the inner surface of coloured seed coats did not therefore explain the slow imbibition of these seeds. The white seed coats loosened rapidly during imbibition whilst the coloured seed coats remained closely associated with the cotyledons suggesting that the adherence of the seed coat to the cotyledons and therefore the ease of access of water between the testa and cotyledons determines the rate of imbibition. The rapid water uptake by white-coated seeds and the subsequent imbibition damage may explain the high incidence of infection of these seeds by the soil-bome fungus Pythhan after 2 d in soil. Improved seed quality and emergence may therefore be achieved by breeding for seed coat characteristics leading to reduced rates of imbibition.