Effect of Light, Temperature, Salinity, and Halopriming on Seed Germination and Seedling Growth of Hibiscus sabdariffa under Salinity Stress

Salt stress is a serious and current global problem for crops. Due to climate change, the soil today has higher salinity levels than in past decades. Identifying temperature, light, and salinity that allow plants to germinate and grow is an ambitious challenge for the future. Hibiscus sabdariffa (H. sabdariffa) is a plant that undergoes abiotic stress during all stages of growth. The aim of this work was to identify the best conditions in terms of light, temperature, and salinity during the germination and growth phases of H. sabdariffa. To improve the germination of H. sabdariffa seed, the effects of abiotic stress were investigated in three experiments. In the first experiment, the factors included light at two levels (light and dark cycles) and temperature at eight levels (5, 10, 15, 20, 25, 30, 35, and 40 °C). In the second experiment, the effect of salinity was examined at seven levels (0, 30, 60, 90, 120, 150, and 180 mM NaCl). In the third experiment, the factors consisted of seed halopriming at two levels (0 and 180 mM NaCl for 24 h) and salinity at seven levels (0, 30, 60, 90, 120, 150, and 180 mM NaCl). The highest germination rate (GR), seedling dry weight, and uniformity of germination were obtained at 30 °C in dark conditions, as reported by one-way Anova analysis. Germination was restricted by temperatures lower and higher than 5 and 30 °C, respectively. By increasing the salinity, all the germination characteristics were decreased, but these effects were less pronounced by halopriming. The most suitable planting date was in the spring, when the temperature was in the range of 25–35 °C. During the germination stage, Hibiscus tea is sensitive to low salinity soils. Halopriming can be performed for enhancing GR and emergence percentage.