Germination, growth and physiological responses of Senegalia senegal (L.) Britton, Vachellia seyal (Delile) P. Hurter and Prosopis juliflora (Swartz) DC to salinity stress in greenhouse conditions
Salinity is among the most widespread environmental threats to global plant production, especially in arid and semi-arid climates. Thus, the selection of salt tolerant species is necessary for sustainable plant productivity. The purpose of this study was to measure and understand the salt tolerance of three multipurpose trees used in reforestation programs in many Sahelian countries (Senegalia senegal, Syn. Acacia senegal; Vachellia seyal, Syn. A. seyal, and Prosopis juliflora). The effect of salinity was evaluated at seed germination stage on Petri dishes containing water agar (0.9%, w/v) with seven concentrations of NaCl (0, 86, 171, 257, 342, 428, and 514 mM). Our results showed that all the species had a germination rate higher than 85% at 257 mM. However, it decreased at 342 mM with a reduction of 70 and 20%, respectively for S. senegal and V. seyal. For plants growth and physiological responses, seedlings were individually cultivated in plastic bags (25×12 cm) containing non-sterile soil and watered with four salt solutions (0, 86, 171 and 257 mM NaCl). Four months after the plants’ cultivation, the results showed that for all species, the salinity reduced significantly the height, the collar diameter, the shoot and root dry biomass as well as the total chlorophyll, K+ and K+/Na+ ratio. In the meantime, proline content, Cl- and Na+ accumulation in leaves were increased. It was also found that S. senegal and V. seyal tolerated high concentrations of NaCl (257 mM) and developed physiological and molecular mechanisms, such as salt tolerance genes (NHX1), which allow them to be considered as moderated salt tolerant species and seemed to be potential species for the restoration of salt-affected land as P. juliflora.
Key words: Multipurpose leguminous trees, abiotic stress, salt tolerance, Senegal.