Seed enhancements such as seed priming can be used to improve germination uniformity and accelerate the rate of germination. The study focused on evaluating the interaction between light and temperature effects on germination percentages of osmoprimed tobacco seeds (Nicotiana tabacum L.) of eight flue-cured varieties namely K RK26, K RK28, T29, T64, T65, T66, T71 and T72. Seeds were osmoprimed for a maximum period of five days in different solutions of phytohormones (6-Benzylaminopurine (BA) and Gibberellic Acid (GA3) and a salt (KNO3). The lower water potential of these solutions was achieved by adding an osmoticum (Polyethylene Glycol 8000). The influence of osmotic priming was evaluated by incubating the treated seeds under light and dark conditions at optimal (20/30°C) and supra-optimal (33±2°C) temperatures. The experiment revealed that the eight tobacco varieties, gave lower germination percentages in total darkness at high temperatures (33±2°C) than when imbibed under light at 20/30°C. The non-primed seeds exhibited the least germination performance throughout the entire experiment. Osmopriming T64 and T29, in KNO3+ PEG 8000 was superior in enhancing their germination percentages under dark conditions at 33±2°C. Response of the different varieties was different. K RK26, T65, T71 and K RK28 treated with BA+PEG 8000 recorded the highest germination performance for all the germination attributes used in this study whereas, T66 and T72 had a positive response to GA+KNO3+PEG 8000 and BA+ KNO3+PEG 8000 respectively. Osmotic priming resulted in increased germination percentages, rate of germination and improved germination uniformity of the different tobacco cultivars under supra-optimal conditions. Whereas under these conditions, the non-primed seeds of all the varieties exhibited poor germination performances. Therefore, osmotic priming can be used as a method of enhancing tobacco seed germination under stressful environmental conditions.
Key words: Osmotic priming, germination rate, germination uniformity, germination percentage, Nicotiana tabacum L., BA (6-Benzylaminopurine), GA3 (Gibberellic acid), Potassium (KNO3), Polyethylene Glycol (PEG 8000).
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