Contents lists available at ScienceDirect Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti Effect of light, temperature, and salinity and drought stresses on seed germination of Hypericum ericoides, a wild plant with ornamental potential María José Vicente ⁎ , Eulalia Martínez-Díaz, Juan José Martínez-Sánchez, José Antonio Franco, Sebastián Bañón, Encarnación Conesa Departamento de Producción Vegetal, Instituto de Biotecnología Vegetal, Universidad Politécnica de Cartagena, Paseo Alfonso XIII, 48, 30203 Cartagena, Spain ARTICLE INFO Keywords: Abiotic stresses Seed ecology Urban gardening Osmotic potential Germination recovery Ornamental species ABSTRACT Hypericum ericoides is a rock plant of potential ornamental use in sustainable gardening in Mediterranean urban environment. This study was carried out to investigate the effects of temperature, light, salinity and soil moisture at the stage of plant life most sensitive to abiotic stresses (seed germination). The results indicate that light is not a germination requirement, while temperature the main factor that regulates the germination process of this species. Seed germination was inhibited by warm temperatures of 25 and 30 °C. By contrast, intermediate temperatures of 10, 15 and 20 °C induced high germination percentages both in alternating light/darkness and continuous darkness. The alternating temperature of 12/20 °C led to germination percentages close to 100 % and the highest germination speed, making this the suggested optimal for germination. The germination values attained demonstrated the absence of dormancy in H. ericoides seeds. In general, salinity and drought stress (induced by NaCl and PEG solutes, respectively) caused similar effects, reducing and delaying seed germination as the osmotic potential decreased (from 0 to -1.68 MPa). However, while most non-germinated seeds remained viable during exposure to all the osmotic potentials induced by PEG and germinated when drought stress was alleviated, the highest levels of salt stress permanently inhibited germination, although not in all seeds. These results indicated that germination inhibition under both NaCl and PEG stress is mainly due to the low water potential caused by osmotic stress, while salt stress had the added toxic effect of specific ions at the highest concentrations of NaCl. So, H. ericoides seeds can germinate well under conditions of moderate salinity and high drought stress, making it a promising species for use in sustainable urban gardening, with a low input of irri- gation water of low quality. 1. Introduction The genus Hypericum L (Guttiferae) includes about 488 species of shrubs, perennial and annual herbs, and more infrequently, trees with a worldwide distribution (Robson, 2012). Many Hypericum species are medicinal plants used by traditional medicine systems in many coun- tries around the world, or are sold as ornamentals (Crockett and Robson, 2011). Among the wild species, Hypericum ericoides is a rock plant that can be considered of potential use as an ornamental species for sustainable gardening in Mediterranean urban environments, as we will justify later. It is an evergreen dwarf shrub (2-40 cm) that grows in a cracks in the calcareous rock or scree on calcareous soils in the east and south-east of the Iberian Peninsula (Castroviejo et al., 1993). Its stems are articulated and very branched, with 4 longitudinal lines at the internodes. The leaves range in size between 1–4.5 and 0.5-0.8 mm (length/width ratio: 3–7), are whorled in groups of four, densely imbricated, from linear to lanceolate and recurved in shape, papillose, with translucent glands. Its flowers, which start to bloom in May and continue to bloom throughout summer, are often yellow in colour, and have five petals 4-7 mm in length. The seeds are brown and 0.9-1 mm long. Mediterranean species of wild flora are of increasing interest for use in semi-arid climate garden designs because of their capacity to adapt to adverse environmental conditions: hot day and low night temperatures, drought and salinity (Franco et al., 2006). In addition, due to their endemic origin, Mediterranean species represent the most suitable ve- getation for tolerating the stresses of urban environments (Benvenuti et al., 2016). In this type of species, succulent leaves, compact twiggy growth, small evergreen leaves with a thick cuticle are all adaptations to water loss, necessary characteristics in plants exposed to the climatic conditions of semi-arid gardens (Dunnett and Kingsbury, 2004). Many of these characteristics are present in the rock plant H. ericoides, which https://doi.org/10.1016/j.scienta.2020.109433 Received 7 October 2019; Received in revised form 12 April 2020; Accepted 14 April 2020 ⁎ Corresponding author. E-mail address: maria.vicente@upct.es (M.J. Vicente). Scientia Horticulturae 270 (2020) 109433 0304-4238/ © 2020 Elsevier B.V. All rights reserved. T