COMPARISONS OF THE STORAGE POTENTIAL OF CULTIVARS OF COWPEA (VIGNA-UNGUICULATA) DIFFERING IN SEED COAT PIGMENTATION

Five cowpea cultivars differing in seed coat pigmentation were stored under simulated Ghanaian conditions (30 degrees C, 75.5% rh) for 6 mon ths and accelerated ageing conditions (40 degrees C 100% rh) for 6 d. Pigmented cultivars retained high germinations throughout the storage period whereas those of the unpigmented cultivars declined. All cultiv ars showed increased seed leachate conductivity and reduced staining o f the cotyledons with tetrazolium chloride as storage time increased a lthough in both storage conditions, the unpigmented cultivars deterior ated far more rapidly possibly due to the greater increase observed in their seed moisture content (mc) when held at the high relative humid ity. Unpigmented cultivars also deteriorated more rapidly during contr olled deterioration at a constant me (20%) and 40 degrees C indicating that they are also genetically more predisposed to rapid deterioratio n than are pigmented cultivars. Imbibition damage did not occur in uns tored seeds whereas the reduced vital staining of the cotyledons after rapid imbibition of stored i.e. aged seeds revealed the incidence of imbibition damage. In pigmented seeds the incidence of imbibition dama ge in seeds that had aged in store could have been partly due to the i ncrease in the rate of imbibition observed after storage. However the rate of imbibition of the unpigmented cultivars remained unchanged sug gesting an increased predisposition of the aged seeds to imbibition da mage. The interaction of seed ageing during storage and imbibition dam age in their influence on seed quality is discussed.