Enhancement of okra (Hibiscus esculentus) seedling growth and emergence by heat stress conditions

Abstract

SUMMARYSeeds of okra were sown in moist soil and subjected to heat stress of 45 °C for 10 h on day 0 (day of sowing), day 1 or day 2 after sowing. Stresses on day 0 and, to a lesser extent, on day 1 promoted hypocotyl elongation and accelerated seedling emergence. Stress on day 2 retarded hypocotyl elongation and did not accelerate emergence. The results were similar for seeds sown at depths of 1, 4 or 7·5 cm. For 10-h stresses on day 0, 40 °C was slightly less promotive than 45 °C; but 50 °C or above resulted in no emergence whatsoever. Subjecting dry seeds to 40–60 °C for 24 h before sowing gave no appreciable acceleration of emergence; instead, at 60 °C there was a 24-h delay in the onset of emergence. Seeds were also incubated for 1·5 h in water at temperatures ranging from 40 to 80 °C. Emergence was accelerated at 40 to 65 °C, with the greatest acceleration at 45 °C. It is suggested that incubating the seeds at 45 °C for 1·5 h before sowing could afford a practical means to accelerate field emergence of okra.