Germination of semi-hard seeds and non-semi-hard seeds of 'Maffei 15' limabean 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 clas ses: 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 hou rs at 25 degrees C were considered to be semi-hard seeds (SHS). Light, medi um and heavy seeds had 60, 42 and 13% SHS, respectively, SHS having lower i nitial moisture concentration than non-SHS. Relative to non-SHS, SHS had gr eater percentage germination (at constant 25 degrees C) and percentage emer gence (of normal seedlings in a greenhouse), and higher shoot dry weights a t 12 days after emergence. Shoot dry weights were positively related to see d weight. For seeds not separated into SHS or non-SHS, matric priming in fi ne exfoliated vermiculite (4d, 15 degrees C, -0.5 MPa, 1:2.5 seed:vermiculi te weight ratio) increased germination at constant 25 degrees C to an avera ge 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 fail ed to increase the germination percentage of non-SHS. Thus, seeds determine d to be non-SHS were injured in response to rapid imbibition during the 4-h our water soak. Non-SHS seeds not given the water soak exhibited improved g ermination, emergence and seedling growth in response to slowed imbibition resulting from matric priming.