Exploring the potential of Solanum pennellii and Solanum peruvianum as rootstocks for enhancing thermotolerance of tomato plants

Drought-tolerant tomato wild relatives Solanum pennellii and S. peruvianum show heat-tolerant responses, but their use as rootstocks to enhance thermotolerance has not been examined. This study investigated the effects of heat stress on tomato plants grafted onto commercial ‘Maxifort’ and wild relatives S. pennellii and S. peruvianum rootstocks in high tunnel, open-field and growth chamber experiments. Heat-tolerant ‘Celebrity’ and heat-sensitive ‘Arkansas Traveler’ cultivars were used as scions, and non-grafted (high tunnel, open-field) or self-grafted plants (growth chamber) were used as controls. The high tunnel and open-field experiments were conducted in the spring (March – June) and summer (June – September) for control and heat treatment, respectively, with daily high/low average temperatures of 27.5/19.0 °C and 33.2/22.5 °C in the high tunnel and 28.2/17.5 °C and 33.8/23.1 °C in the open-field. The growth chamber experiment was conducted at 38/30 °C (day/night) and 26/19 °C for the heat and control treatments, respectively, for 21 days. The shoot and root growth of S. peruvianum and S. pennellii-grafted tomato plants were adversely affected by potential low graft compatibility resulting from interspecific grafting and their limited adaptability to the open-field soil environment, regardless of stress conditions. S. pennellii-grafted plants showed heat-sensitive responses in root biomass and architecture, leaf chlorophyll fluorescence, electrolyte leakage and relative water content depending on the environment, indicating its unsuitability as a rootstock under heat stress. On the other hand, plants grafted onto S. peruvianum exhibited heat-tolerant responses in physiological aspects, including the gas exchange, leaf chlorophyll, carotenoid and amino acid in the growth chamber, fruit yield in the high tunnel, and chlorophyll fluorescence in both experiments. We suggest that S. peruvianum could be utilized as effective breeding material for developing interspecific hybrid rootstocks with thermotolerance and increased graft compatibility between scion and rootstock to improve shoot and root growth of grafted plants. •Low graft compatibility inhibited shoot and root growth of tomato plants grafted onto wild relatives.•S. peruvianum showed thermotolerance in physiological parameters in growth chamber.•S. pennelliii was heat susceptible as a rootstock in morpho-physiological parameters.•S. peruvianum and S. pennelliii showed low adaptability to open field