Improving the Salt Tolerance of “Old Limachino Tomato” by Using a New Salt-Tolerant Rootstock

Salinity is a major constraint limiting the yield of tomatoes. However, grafting strategies may help to overcome the salt toxicity of this important horticultural species if appropriate rootstocks are identified. The present study aimed to test a new rootstock, JUPAFORT1, obtained by crossing the glycophyte Solanum lycopersicum (cv. Poncho Negro) with the halophyte wild-related species Solanum chilense to improve the salinity tolerance of the Chilean tomato landrace Old Limachino Tomato (OLT). Intact OLT plants were exposed to 0, 80, or 160 mM of NaCl for 21 days at the vegetative stage and compared with self-grafted (L/L) and Limachino plants grafted on JUPAFORT1 rootstock (L/R) under a completely randomized design. JUPAFORT1 increased OLT scion vigor in the absence of salt but did not significantly increase fresh weight under stress conditions. However, JUPAFORT1 confers to the scion an anisohydric behavior contrasting with the isohydric behavior of L and L/L plants as indicated by measurements of stomatal conductance; L/R plants were able to maintain their metabolic status despite a slight decrease in the leaf’s relative water content. JUPAFORT1 rootstock also enabled the maintenance of photosynthetic pigment concentrations in the scion in contrast to L and L/L plants, which exhibited a decrease in photosynthetic pigments under stress conditions. L/R plants encountered oxidative stress at the highest stress intensity (160 mM of NaCl) only, while L and L/L plants suffered from oxidative damage at a lower dose (80 mM of NaCl). L/R plants behaved as includer plants and did not sequester Na+ in the root system, in contrast to L and L/L, which behaved as excluder plants retaining Na+ in the root system to avoid its translocation to the shoots. The expression of genes coding for ion transporters (HKT1.1, HKT1.2, LKT1, SKOR, SOS2, and SOS3) in the root system was not modified by salinity in L/R. In contrast, their expression varied in response to salinity in L and L/L. Overall, L/R plants exhibited higher physiological stability than L/L or L plants in response to an increasing NaCl dose and did not require additional energy investment to trigger an adaptative response to salinity. This suggests that the constitutive salinity tolerance of the halophyte S. chilense was maintained in the interspecific rootstock. JUPAFORT1 issued from S. lycopersicum x S. chilense may thus improve salt-stress resilience in OLT tomatoes. Additional studies are required to identify the molecular components involved in the root-to-shoot signaling pathway in this promising material.