Seed development in the recalcitrant species Quercus robur L.: germinability and desiccation tolerance

Changes in germination and desiccation sensitivity were measured throughout the seed expansion phase of development in fruits of Quercus robur L. The onset of a reduction in sensitivity to desiccation during development on the tree coincided with acquisition of the capacity for seed germination on moist sand substrate. Tolerance of desiccation then increased throughout development to shedding, but viability was still lost at a relatively high moisture content, and seeds did not therefore pass through a fully desiccation-tolerant phase. These data suggest that desiccation sensitivity in Q. robur may have resulted from the premature termination of development. No desiccation was required to initiate germination in prematurely harvested fruits or seeds. Germination rate of seeds on moist sand increased at successive harvests during development, and was also increased by presoaking seeds in water. Variation in germination rate following shedding was not related to seed size or moisture content, but was affected by shedding date. This effect was not observed when the pericarp was removed