Long-term salt stress influence on vegetative growth and foliar nutrient changes in mango (Mangifera indica L.) seedlings

Salinity is one of the main environmental threats for crop production worldwide, especially in arid and semi-arid lands. In general, mango species are considered sensitive to salinity stress. For instance, effects of salt stress on seedling growth inhibition, reduction of chlorophyll content, net CO2 assimilation and nutrient uptake have been previously reported. To characterize the magnitude of tolerance or susceptibility to salt stress, seedlings of two mango rootstocks ('13/1' and 'Gomera-3') were exposed to 50 mM NaCl in water solution during 175 days. Data showed that salt concentration differentially affected the functional leaf number in both rootstocks. Thus, while no effects of salt stress occurred in '13/1' rootstocks at least during the first four months after the beginning of salt treatment, 'Gomera-3' rootstocks suffered a reduction of their leaf number since the sixty-four day after the stress onset. Salt treatment reduced leaf fresh and dry weights in 'Gomera-3' seedlings; however, salt stress did not alter leaf biomass in '13/1' plants. In contrast, salinity induced an earlier and greater decrease of relative stem length growth (RSLG) in '13/1' than in 'Gomera-3' seedlings. Regarding plant nutritional status, salinity increased Na+ and Cl- concentrations in both rootstocks, and K+ only in '13/1'; however, salt stress did not alter many of the analyzed nutrients. In addition, salt stress induced proline production in the studied rootstocks, although irrespective of treatments, content was higher in 'Gomera-3' than in '13/1' plants. Both rootstocks exhibited an increase of MDA content induced by salinity stress. In conclusion, several observations, such as the delay of leaf abscission establishment, the pattern of increase of K+ and proline content induced by long-term salt stress, indicate that '13/1' rootstocks appear more tolerant to the applied salt stress conditions than 'Gomera-3'.