Effect of abiotic stresses on germination behaviour of Ruta chalepensis

This work aims to highlight the optimal temperature for the seed germination of Ruta chalepensis, an important threatened ethnomedicinal shrub, and assess its germination tolerance against salinity and water stresses as well. For this, the seeds were incubated firstly under different temperatures (5 to 30°C). After that, at 20°C, germination tests were performed under different sodium chloride (NaCl) concentrations (0 to 273.9 mM) and various polyethylene glycol solutions (PEG6000) (0 to -2.20 bar). Final germination percentage, velocity coefficient and latency time were subsequently the germination patterns determined and analysed. The optimum temperature for germination was 15°C, in which the maximum final germination percentage (85%) was noticed; germination fell steadily, however, above and below this temperature and completely ceased at 30°C. Germination behaviour of R. chalepensis seeds under osmotic stress conditions showed a significant effect of both NaCl and PEG6000. Germination decreased whether sodium chloride or polyethylene glycol was increased in the medium (p < 0.05). Moreover, the salinity tolerance threshold was 205.4 mM, equivalent to 16 g L-1 NaCl, while water stress was -1.16 bar, corresponding to 80 g L-1 PEG6000. Beyond these thresholds, germination stopped. Dropping in velocity coefficient and postponing in latency time with increasing both stresses were recorded either. The sensitivity of R. chalepensis seeds to environmental stresses should be taken into account for successful conservation programmes, which should be implemented by sowing seeds and planting seedlings in fresh habitats with sufficient annual rainfall.