Phosphoric acid-assisted constant relative humidity chambers utilized for controlled deterioration of rice seeds

Constant relative humidity (RH) chambers using phosphoric acid (PA) are useful for controlled desiccation of pollen and in vitro cultured materials for cool-dry storage or cryopreservation (Ishikawa et al., 2005, Ishikawa and Oda, 2008). Here we demonstrate that the chambers are also convenient for accelerated ageing of seeds. Rice seeds 3-11 years old (stored at 8-9°C) were artificially aged for 0-41 days in PA-assisted relative humidity (RH) chambers (RH 93%) placed in an incubator set at 37°C. At designated time periods during ageing, vigour and longevity of the seeds with different storage history were evaluated by monitoring germination timecourse and seedling shoot and root growth. Under these ageing conditions, seeds harvested in 2002 had half germinability (50% longevity) period of 33 days while older seeds (stored for longer periods) showed faster decline in germinability, longer lag time before germination, slower rates of germination and reduced shoot and root growth. Root growth was more sensitively affected by storage and accelerated ageing than shoot growth. PA-assisted system is simple, economical and safer than conventional RH chamber systems using saturated solutions or H2SO4 (Winston and Bates, 1960, Solomon, 1951). Various constant RH are available at desired temperatures using a single compound and convenient for realizing controlled deterioration of seeds at various RH and temperature regimes.