Seed germination characteristics of some medicinally important desert plants from the Arabian Peninsula

Abstract

The arid climate of Saudi Arabia supports many medicinally important species. Germination behavior is crucial to their establishment in the face of low rainfall and high summer temperatures that produce high evapotranspiration and salt accumulation in the surface soil. We investigated the seed germination biology of three medicinal species from Wadi ad Dayqah in central Saudi Arabia: Salvia spinosa (Lamiaceae), Ochradenus arabicus, and Ochradenus baccatus (Resedaceae). We examined the responses of freshly collected seed to constant and alternating temperature, light, and salinity (NaCl). None of the species showed innate dormancy. All achieved high germination percentages over a wide range of diurnally alternating temperatures (5/15, 10/20, 15/25, 20/30 and 25/35 °C). However, the range of temperature for successful germination was narrower at constant temperature, especially for S. spinosa. The rates of germination suggested that all the temperatures examined were suboptimal. Basal temperatures for germination were 5–8 °C. Germination of all the species was promoted by light. All were tolerant of salinity up to 80–100 mM NaCl. Osmotically enforced failure to germinate with increasing salinity was reversible after transfer to fresh water. Understanding these adaptive characteristics will assist the development of effective strategies for the conservation of medicinally important species in arid environments.