Comparative Analysis of Tolerance to Salt Stress and Water Deficit in Two Invasive Weeds of the Genus (Asteraceae).

and are two noxious weeds present in many parts of the world. Their tolerance to salinity and water deficit was analysed at the seed germination stage and during vegetative development. Seed germination was tested in solutions with different concentrations of NaCl and polyethylene glycol (PEG). Growth parameters, photosynthetic pigments, ion accumulation, and antioxidant mechanisms were analysed in plants that were subjected to increasing NaCl solutions, or severe water deficit by completely restricting irrigation. Seed germination was mostly affected by NaCl, but less by PEG in both species. had a faster germination in all treatments and maintained a higher percentage of germination under the highest concentration of salt applied. Growth responses were similar in the two species, both being more affected by higher salt concentrations than by water deficit. The main differences in the responses of the two species to stress regard K and proline concentration. K in roots decreased under salt stress in , but remained constant in leaves, whereas in increased in roots and leaves in salt-stressed plants. Proline concentration increased in all plants under salt stress, but only in those under the highest salt concentration in . The results obtained indicate that the two species are relatively tolerant to water deficit and medium salinity but are susceptible to high NaCl concentrations.