Watermelon seed germination. 2. Osmomanipulation of photosensitivity

Abstract

AbstractSeed germination of watermelon (Citrullus lanatus cv. Sugar Baby) was fully suppressed by intermittent far-red (FR) irradiation (1 min every 30 min). When the intervening dark period was increased, a linearly increasing final germination percentage was obtained. However, a 4-day intermittent FR treatment induced phytochrome-controlled dormancy and the longer the dark interval the deeper was the dormancy of the non-germinated seeds. When seeds were soaked in a fully inhibitory osmotic solution, no dormancy was imposed. However, a single FR pulse at the time of transfer induced partial, secondary dormancy; the kinetics of the imposition of dormancy followed a negative exponential curve (half-life 1.5 days; 3 days for the cultivar Crimson Sweet). Seeds osmotreated for 10 days in darkness and subsequently dehydrated (with and without a final FR pulse) acquired germination characteristics similar to those in light-requiring and dark-germinating achenes, respectively, of the lettuce cultivar Grand Rapids. In the light-requiring osmomanipulated seed population, the induction of germination was brought about by the low-energy reaction of phytochrome, chilling, dry storage and decoating. The transformation through osmomanipulation of the dark-germinating watermelon seeds (the inhibition of which required prolonged exposure to light) to positively or negatively photosensitive seeds (that responded to brief light pulses), might be attributed to the slow relaxation of existing meta-Fa and meta-Rb phytochrome intermediates to Pfr upon hydration.