2018 ASHS Annual Conference

Improvement of crop water use is imperative. How plants respond to limited water can dictate their ability to better utilize available resources and avoid prolonged and severe stress. The following study was conducted to determine how tomato (Solanum lycopersicum) rootstocks with different root system morphologies respond to drying soils. Plants were grown in pots containing an inorganic substrate composed of calcined clay and sand in a greenhouse on North Carolina State University’s campus. The heirloom tomato cultivar Cherokee Purple was used as the scion for ‘Beaufort’ and ‘Shield’ rootstocks as well as the self-grafted control. These rootstock treatments were assigned either normal or reduced irrigation treatments. Plants receiving normal irrigation were weighed and watered daily to maintain container capacity for one week. Those receiving reduced irrigation had all water withheld for one week, at which point strong midday wilting became evident. Shoot physiological and morphological data as well as root morphological data were collected at the end of the study. A constitutive positive effect on relative water content, leaf area, stomatal conductance, and net CO₂ assimilation rate was observed with ‘Beaufort’. This rootstock had a significantly longer total root system (118.6 m) compared to ‘Shield’ (94.9 m) and the self-grafted control (104.2 m). Furthermore, 76.40% of the total root length observed in ‘Beaufort’ was composed of very thin diameter roots ( < 0.5 mm), which was higher than ‘Shield’ (73.67%) and the self-grafted control (69.07%). The only significant rootstock irrigation interaction observed was for effective quantum yield of photosystem II (ϕ_PSII). At normal irrigation there were no differences among the rootstock treatments; however, at reduced irrigation ‘Beaufort’ had significantly higher ϕ_PSII than both ‘Shield’ and the self-grafted control. This study represents one of the first to compare both root and shoot morphological and physiological responses to soil drying in grafted tomatoes. These results may explain some of the improved production and water use efficiency observed in field trials utilizing ‘Beaufort’ rootstock and allow for better screening of rootstocks for improved water use efficiency in the future.