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The effects of gibberellic acid (GA3), potassium nitrate (KNO3), prechilling, temperature, salt stress and osmotic potential on seed germination and sowing depth on seedling emergence and burial depth on seed viability of hoary cress (Cardaria draba (L.) Desv.), were studied in a series of laboratory, glasshouse and outdoor experiments. The optimal temperature for hoary cress seed germination was 20°C, both in light/dark and darkness regimes. Seed germination of hoary cress at 400 ppm concentration of GA 3 in a light/dark regime was maximal. Potassium nitrate concentrations increased the percentage of germination in comparison with the control treatment. Increasing the duration of dry prechilling to 30 and 45 days promoted the seed germination of hoary cress. Germination of hoary cress markedly decreased as salt and drought stress increased. Seed germination of hoary cress occurred at a range of pH from 3 to 11. Seedling emergence significantly decreased as planting depth increased. Total seed viability decreased with increasing burial depth. The maximum increase in mortality occurred in seeds that were buried at 5-cm depth.

Shepherd's purse (Capsella bursa-pastoris) is a problematic weed in citrus orchards and crop fields in northern Iran. In a series of laboratory and greenhouse experiments, we evaluated the effects that treatment with gibberellic acid (GA 3 ) and potassium nitrate (KNO 3 ), as well as environmental factors, including temperature, the duration of pre-chilling (wet and dry), drought stress, salt stress, pH, and sowing depth, have on seed dormancy breaking and germination in C. bursa-pastoris. Treatment with GA 3 strongly stimulated germination of C. bursa-pastoris in conditions of light/ dark and continuous darkness. The germination rate was highest (40.08%) for seeds treated with 400 ppm of GA 3 in the light/dark condition. Treatment with KNO 3 did not significantly influence seed germination. Longer wet pre--chilling promoted germination and was more successful in seed dormancy breaking than was dry pre-chilling. Seed germination occurred at 10-30°C and within a range of pH of 3-11. Drought and salt stress both strongly inhibited germination. Seedling emergence decreased in proportion to sowing depth. The rates of C. bursa-pastoris germination and seedling emergence were highest for seeds on the soil surface.

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Seed dormancy is a common strategy of many plants to survive in natural and agricultural ecosystems. This study examined the effects of some chemical factors, including gibberellic acid and potassium nitrate, the prechilling temperature, duration and conditions and the light regimes on the seed dormancy-breaking of Papaver rhoeas L. and Papaver dubium L. The results showed that all the tested seed dormancy-breaking treatments significantly stimulated the germination of the two Papaver species. The seed germination was significantly influenced in relation to the seeds that were treated with 0-1250 p.p.m. of gibberellic acid. The maximum germination was observed in P. rhoeas L. at 750 p.p.m. and in Pa. dubium L. at 500 p.p.m. in the light/dark regime. There was a significant increase in the germination with an increase in the potassium nitrate concentration. The greatest germination was achieved at the lowest potassium nitrate concentration (0.5 g L −1 ) in the light/dark regime. The wet prechilling was more effective than the dry prechilling in the dormancy-breaking of both P. rhoeas L. and Pa. dubium L. The highest germination percentage was found in the wet prechilling condition after 45 days' prechilling duration. The combination of gibberellic acid and potassium nitrate was more successful than their separate application in the stimulation of germination in both Papaver species. Among the combined treatments of prechilling and gibberellic acid, the highest germination of P. rhoeas L. was recorded in the seeds that were treated with wet prechilling for 45 days with 750 p.p.m. gibberellic acid, while in Pa. dubium L., the maximum germination was recorded with wet prechilling for 45 days with 500 p.p.m. of gibberellic acid.