Effect of seed moisture content and cooling rate in liquid nitrogen on legume seed germination and seedling vigour

The effects of seed moisture content and cooling rate (in liquid nitrogen) on seed germination and seedling vigour (germination × radicle length) were studied in single seed lots of four legume species: lucerne (Medicago sativa), pea (Pisum sativum), cowpea (Vigna unguiculata) and bean (Phaseolus vulgaris). Five moisture contents and four cooling rates (30, 130, 1650 and 2800°C/min) were studied for each species. The fastest cooling rate was achieved using subcooled liquid nitrogen (−210°C). All cooling treatments improved lucerne seed germination, probably due to breaking hard seed through scarification. Pea, cowpea and bean seeds humidified for four weeks in a saturated atmosphere (21.5, 18.0 and 16.8% moisture content f.w.b., respectively) showed a decrease in germination and seedling vigour when cooled at the fastest two rates. However, those seeds cooled at 130°C/min showed improved seedling vigour with respect to control seeds. Desiccation reduced germination and seedling vigour in bean seeds. A study performed only with non-cooled and cooled seeds at 130°C/min showed that germination and seedling vigour increased with humidification prior to sowing.