GERMINATION OF SEMI-HARD SEEDS AND NON-SEMI-HARD SEEDS OF 'MAFFEI 15' LIMA BEAN IN RESPONSE TO MATRIC PRIMING

A commercial seedlot of fungicide-treated 'Maffei 15' lima bean (Phaseolus lunatus L.; ASI, Ordbend, CA) was separated into 3 seed air dry weight classes: light (275–325 mg, medium (375–425 mg), and heavy (475–525 mg). Seeds with little or no change in weight or size after soaking in water for 4 hours at 25 °C were considered to be semi-hard seeds (SHS). Light, medium and heavy seeds had 60, 42 and 13% SHS, respectively, SHS having lower initial moisture concentration than non-SHS. Relative to non-SHS, SHS had greater percentage germination (at constant 25 °C) and percentage emergence (of normal seedlings in a greenhouse), and higher shoot dry weights at 12 days after emergence. Shoot dry weights were positively related to seed weight. For seeds not separated into SHS or non-SHS, matric priming in fine exfoliated vermiculite (4d, 15°C, -0.5 MPa, 1:2.5 seed:vermiculite weight ratio) increased germination at constant 25°C to an average 96%, compared to 81%, 70% and 68% for light, medium and heavy seeds that were not primed. For seeds separated into SHS and non-SHS, matric priming failed to increase the already high germination percentage of SHS, and failed to increase the germination percentage of non-SHS. Thus, seeds determined to be non-SHS were injured in response to rapid imbibition during the 4-hour water soak. Non-SHS seeds not given the water soak exhibited improved germination, emergence and seedling growth in response to slowed imbibition resulting from matric priming.