The Effects of After-ripening, Heat and Nitric Acid on Seed Dormancy of Four Local Cultivars of Padi (Oryza sativa L.)

Four local cultivars of padi, namely MR 71, MR 73, MR 77 and IR 42, have more than 80% dormant seeds when freshly harvested. After-npening, especially in the air-conditioned room was effective in overcoming their dormancy and increasing germination to more than 80% and 90% after eight and sixteen weeks respectively. Heat and nitric acid treatments were less effective than afternpening. Except for MR 71 where dormancy was less severe, germination of only 78%, 72% and 69% was 0 btained for MR 77, MR 73 and IR 42 respectively with the best heat or nitric acid treatments. Exposure to 45°C for four days was best. The effect of nitric acid van'es between van'eties. For MR 71 and MR 73, soaking for 6 -12 hours in 0.3 M nitric acid was optimal. For MR 77 and IR 42, soak"" in 0.5 M nitric acid for 3 - 6 hours and 12 hours respectively was best. The practical implications of \ the study are discussed

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