CANOLA SEED-GERMINATION AND SEEDLING EMERGENCE FROM PRE-HYDRATED AND RE-DRIED SEEDS SUBJECTED TO SALT AND WATER STRESSES AT LOW-TEMPERATURES

Low soil temperatures and low water potentials reduce and delay the se ed germination of canola (Brassica rapa L., B. napus L.) in western Ca nada. Germination is also very sensitive to the salinity effects of ni trogen fertiliser placed with the seed, especially when the seed bed i s relatively dry. The effects of pre-hydration and re-drying treatment on canola (Brassica rapa L. cv. Tobin) seed germination and seedling emergence at 10 degrees C subjected to either a water or salt stress w ere determined. Low water potentials, induced by polyethylene glycol ( PEG 8000), low soil moisture, or high concentrations of salts, reduced both germination and seedling emergence, and increased the time to 50 % germination and emergence of seeds at 10 degrees C. At equal osmotic potentials, Na2SO4 was less inhibitory on low temperature germination than either NaCl or PEG, suggesting that the sulphate ion partially a lleviated the inhibitory effects of low water potential. Solutions of NaCl produced more abnormal seedlings compared to Na2SO4, suggesting t hat NaCl was more toxic than Na2SO4 during seedling development. Pre-h ydration and re-drying partially overcame the inhibitory effects of bo th low water potential and salts on seed germination and seedling emer gence at 10 degrees C. The seed treatment increased the germination ra te in Petri dishes and seedling emergence from a sandy loam soil. Wate r potentials or soil water contents required to inhibit 50% germinatio n or emergence at 10 degrees C were lower for treated seeds compared t o control seeds. Salt concentrations inhibiting 50% emergence were hig her for treated seeds than control seeds. Neither treated nor control seeds produced seedlings which emerged if the soil water content was l ower than 9% or when the soil was continuously irrigated with salt sol utions of 100 mmol kg(-1) of NaCl or 50 mmol kg(-1) of Na2SO4. These r esults suggest that the pre-hydration and re-drying treatment did not lower the base water potentials at which seedling emergence could occu r. Abnormal seedlings were observed in both treated and control seeds, particularly if the soil was watered with NaCl solutions; however, th e seed treatment reduced the number of abnormal seedlings.