Grafting onto wild tomato species: A viable strategy against combined abiotic stress?

Wild tomato species (WTS) have long been attracting the attention of plant researchers due to their ability to tolerate harsh environmental conditions in their natural habitats. In this context, their use in grafting procedures, where they serve as rootstocks, has been proposed as a strategy to enhance the stress resilience of cultivated tomato. However, insights into the effectiveness of this approach are still needed to understand its real potential. Thus, this study evaluated whether grafting tomato plants (cv. Chico III) onto WTS rootstocks (Solanum habrochaites LA1223 and Solanum galapagense LA1403) could improve growth and physiological performance under combined drought (limited irrigation) and salinity (200 mM NaCl) stress. Biometrical and photosynthetic parameters were evaluated in grafted and non-grafted plants, before and after stress exposure, and stress-induced changes in biochemical endpoints were also assessed. Grafting onto WTS delayed scion growth and did not prevent the reductions in photosynthesis, growth, or reproductive output observed under stress conditions. Still, the use of wild rootstocks contributed to some physiological adjustments, including enhanced photosystem II efficiency under control conditions and improved antioxidant and osmotic regulation under stress, although these effects were insufficient to fully counteract the impact of combined drought and salinity. These findings indicate that, under severe yet relevant conditions of combined abiotic stress, grafting onto WTS alone is not enough to improve tomato plant resilience. Importantly, this study provides novel insights into rootstock-mediated physiological responses and highlights species-specific stress adjustments among WTS, offering valuable information for future integrated stress mitigation strategies.