The effect of chilling and moisture status on the germination, desiccation tolerance and longevity of Aesculus hippocastanum L. seed

Effects of 2 degrees C chilling on the threshold moisture contents and water potentials for various physiological processes were estimated for Aesculus hippocastanum L. seed. Seed harvested at the time of maximum seed fall exhibited a dual response to drying: partial drying from near 50% to 32-40% moisture content progressively increased germination percentage (at 16 degrees C) up to various peak values; further desiccation was detrimental, confirming that the seeds are 'recalcitrant'. The moisture content for optimum germination was increased by at least 10% as the chilling period was raised from 0 to 9 weeks. A negative linear relationship was found between log10 mean time to germinate and probit final germination, regardless of pre-treatment, indicating that partial desiccation and chilling are interchangeable in promoting germination of hydrated seed. For nearly fully hydrated seeds, increasing the chilling period from 6 to 26 weeks increased the viability-loss onset point for desiccation injury from near 40% to about 48% moisture content without altering the drying rates of seed tissues. Extending moist chilling in various seed lots from 0 to 26 weeks decreased subsequent longevity at 16 degrees C. For 26-week-chilled seeds longevity (the period to lose one probit of germination) differed above and below a threshold moisture content of 48%. It remained constant in the moisture-content range 48-38%, but increased progressively as moisture content was raised above 48%. This threshold moisture content coincided with the value above which chilled seed pre-germinated in storage. The results indicate that post-harvest desiccation and chilling alter the water relations of various physiological processes and a schematic summary is presented which relates the results to an axis water sorption isotherm.