Varietal Differences in Light Requirements for Germination of Celery (Apium graveolens L.) Seeds and the Effects of Thermal and Solute Stress

Abstract

Seed germination in one wild and two cultivated varieties of celery (Apium graveolens L.) was found to be light-dependent and mediated through the phytochrome system. Seeds of cv. Florida at 20°C were very sensitive to light and germination could be promoted by green safe light as well as by short far-red irradiation of brief duration, while seeds of wild celery did not respond to far-red and were less responsive to green safe light. At the optimal temperature, continuous irradiation with white light caused maximal germination in all varieties. The need for light could be satisfied in cv. Florida by two daily short irradiations. In wild celery, more than six short irradiations were needed, while in cv. Alabaster short irradiations did not bring about the full light effect. Daily alternating temperatures also could replace the light requirement. Two varieties, cv. Florida and the wild, differ in their tolerance to high temperature. Seed germination of wild celery is more thermophilic than that of cv. Florida. Thermodormancy is induced by 35°C of shorter duration in seeds of cv. Florida than in those of wild celery. Light enhanced the induction of thermodormancy. Solute stress increased the number of short irradiations required for germination.