Heat-Induced Inactivation of Seed Germination in Canola (Brassica napus), Grain Amaranth (Amaranthus caudatus), and Proso Millet (Panicum miliaceum)

Trade of grain crops across international borders where live seeds, especially weed seeds, present a problem in obtaining import permits from plant inspection services requires a simple, cost effective treatment to inactivate the problem seeds.  One potential method of inactivating weed seeds is through heat treatment. However, little information is available on temperatures that inactivate weed seed germination but do not affect the utility of the grains. We evaluated the influence of heat treatment on the germination of Canola (Brassica napus), Grain Amaranth (Amaranthus caudatus) and Proso Millet (Panicum miliaceum) seeds as a reference. Most seeds maintained good germination (70-90%) after they were exposed to 80-100 ^oC for up to 40 minutes inside drying ovens. When seeds were exposed to 110, 120, 130 ^oC for 5, 10, 15, and 20 min in the oven, percent seed germination varied from 82.8% to 0%, depending on the temperature and exposure time. When treated with the same range of temperature (110, 120, 130 ^oC) for up to 20 minutes, canola, grain amaranth, proso millet seeds lost germination completely after they were exposure to 110 ^oC for 10 min, 120 ^oC for 15 min, 110 ^oC for 15 min, and 110 ^oC for 5 min, respectively. When proso millet seeds were treated with a commercial flame burner (grain roaster) at seven different temperatures (82, 96, 99, 104, 110, 116, 118 ^oC) for one minute, they became completely incapable of germinating. Heat inactivation of weed seed germination appears to be a promising practice. For seed germination inactivation, the flame burner appears to be more efficient in term of treatment time and energy requirement especially for large volume handling than does an oven type of process.