Water Relations of Seed Development and Germination in Muskmelon (Cucumis meloL.)

Abstract

The effects of storage conditions on the germination of developing muskmelon (Cucumis melo L.) seeds were tested to determine whether after-ripening is required to obtain maximum seed vigour. Seeds were harvested at 5 d intervals from 35 (immature) to 60 (fully mature) days after anthesis (DAA), washed, dried, and stored at water contents of 3-3 to 19% (dry weight basis) at 6, 20, or 30 °C for up to one year. Germination was tested in water and in polyethylene glycol 8000 solutions (-0-2 to — 1-2 MPa osmotic potential) at 15, 20, 25 or 30 °C. Germination percentages and rates (inverse of mean times to radicle emergence) were compared to those of newly harvested, washed and dried seeds. For 40 and 60 DAA seeds, one year of storage at < 20 °C and water contents <6-5% significantly increased germination percentages and rates at 20 °C, but had little effect on germination at 25 and 30 °C. Storage reduced the estimated base temperature (7'b) and mean base water potential (j/Tb) for germination of both 40 and 60 DAA seeds by approximately 5 °C and 0-3 MPa, respectively. Immature 35 DAA seeds showed the greatest benefit from storage at 3 to 5% water content and 30 °C, as germination percentages and rates increased at all water potentials (</i). Storage under these same conditions had little effect on the germination of mature seeds in water, but increased germination percentages and rates at reduced </i's. Accelerated ageing for one month at 30 °C and water contents from 15 to 19% increased germination rates and percentages of mature seeds at reduced i/i's, but longer durations resulted in sharp declines in both parameters. Immature seeds lost viability within one month under accelerated ageing conditions. An after-ripening period is required at all stages of muskmelon seed development to expand the temperature and water potential ranges allowing germination and to achieve maximum germinability and vigour. Post-harvest dormancy is deepest at the point of maximum seed dry weight accumulation and declines thereafter, both in situ within the ripening fruit and during dry storage.