Imbibition Period as the Critical Temperature Sensitive Stage in Germination of Lima Bean Seeds

Abstract

Sumiiimarv. Lima bean seeds (Phaseolus lutnatuts L.) and excised embryonic axes can be injured during imbibition at temperatures below 250. The early imbibitional stage is critical; imbibition at 250 followed by low temperature exposure does not cause injury. Sensitivity to chilling injury is conditioned by the pre-harvest seed history. Low vigor (bleached) seeds are most sensitive to injury, 'the effects of which can be intensified by restricted oxygen supply dulring early axis growth. The seed coat, by preventing water uptake, can permit the seed to avoid injury. This protective mechanism is most ef- fective at low temperature and high moisture stress. Immediately following low temper- ature imbibition, injured axes lose organic materials, probably nucleotides. This organic leachate is a potential influence on soil microorganisms and, together with the tempera- ture sensitivity, vigor, and seed coat effect undoubtedlv is important in controlling the potential variability in germination shown by a seed population.