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 f or Aesculus hippocastanum L. seed. Seed harvested at the time of maxim um seed fall exhibited a dual response to drying: partial drying from near 50 % to 32-40 % moisture content progressively increased germinat ion percentage (at 16 degrees C) up to various peak values; further de siccation was detrimental, confirming that the seeds are 'recalcitrant '. The moisture content for optimum germination was increased by at le ast 10 % as the chilling period was raised from 0 to 9 weeks. A negati ve linear relationship was found between log(10) mean time to germinat e and probit final germination, regardless of pre-treatment, indicatin g that partial desiccation and chilling are interchangeable in promoti ng germination of hydrated seed. For nearly fully hydrated seeds, incr easing the chilling period from 6 to 26 weeks increased the viability- loss onset point for desiccation injury from near 40 % to about 48 % m oisture content without altering the drying rates of seed tissues. Ext ending moist chilling in various seed lots from 0 to 26 weeks decrease d subsequent longevity at 16 degrees C. For 26-Neek-chilled seeds long evity (the period to lose one probit of germination) differed above an d below a threshold moisture content of 48 %. It remained constant in the moisture-content range 48-38 %, but increased progressively as moi sture content was raised above 48 %. This threshold moisture content c oincided with the value above which chilled seed pre-germinated in sto rage. The results indicate that post-harvest desiccation and chilling alter the water relations of various physiological processes and a sch ematic summary is presented which relates the results to an axis water sorption isotherm. (C) 1998 Annals of Botany Company.