Osmo-priming with seaweed extracts enhances yield of salt-stressed tomato plants

Salinization of agricultural land is an expanding phenomenon, which requires a multi-level strategy to counteract its deleterious effects on crop yield and quality. Plant biostimulants are increasingly used in agriculture with multiple purposes, including protection against abiotic stresses such as drought and salinity. The complex nature of plant biostimulants, however, makes it diffcult to establish a cause-effect relationship between the composition of the commercial product and its expected effects. Here, we demonstrate that field applications of two algal derivatives (Rygex, R and Super Fifty, SU) cause a 26% reduction in shoot biomass and a remodulation of the root-to-shoot ratio under moderately saline irrigation (6.3 dS m-1). Moreover, plants treated with the two algal derivatives showed lower leaf water potential and improved water use efficiency under control conditions, suggesting an osmo-priming effect by these two products. These pre-adaptation responses increased tomato yield by 49% (R) and 70% (SU) regardless of the salinity level, with a remarkable reallocation of the biomass toward the fruits. Overall, our results suggest that the application of these two biostimulants can be useful in the open field to protect tomato plants from osmotic stress due to seasonal salinization, a phenomenon that typically occurs in arid and semi-arid environments.