2018 ASHS Annual Conference

Tomatoes (Solanum lycopersicum) are a warm-season, cold-sensitive crop that show depression in growth and development with temperatures below 18 °C. Improving suboptimal temperature tolerance would allow for earlier planting of field-grown tomatoes as well as a reduction in energy inputs for heating greenhouses. Grafting tomatoes onto high-altitude wild Solanum habrochaites accessions has proven effective at improving scion suboptimal temperature tolerance. The following study was conducted to determine whether commercially available tomato rootstocks with differing parental backgrounds and root system morphologies can improve scion suboptimal temperature tolerance. Two controlled environment growth chambers were utilized and maintained at either optimal (25 °C day / 20 °C night) or suboptimal (15 °C day / 15 °C night) temperatures. The cold-sensitive tomato cultivar Moneymaker was used as the non-grafted and self-grafted control as well as scion on ‘Multifort’, ‘Shield’, and S. habrochaites LA 1777 rootstocks. We found that ‘Multifort’ rootstock significantly reduced the amount of cold-induced leaf area reduction and maintained higher levels of CO₂ assimilation and photosystem II quantum efficiency. ‘Multifort’ maintained significantly longer roots, having 42% to 56% more fine root (diameter less than 0.5 mm) length compared to the other rootstock treatments. Leaf starch concentration was significantly lower in ‘Multifort’-grafted plants at suboptimal temperatures. The ability for ‘Multifort’ to maintain root growth at suboptimal temperatures may improve root system sink strength, thus allowing for proper movement of photosynthate from leaf to root even under cold conditions. This study represents one of the first attempts to characterize whole root system morphology responses in tomato rootstocks at suboptimal temperatures. Furthermore, we show that commercially available rootstocks can be selected to improve suboptimal temperature tolerance in cold-sensitive scions at early stages of plant development.