Improvement of crop water use is imperative. Plants’ responses to limited water can dictate their ability to better use 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 rootstocks were assigned either normal or reduced irrigation treatments. Plants grown under the normal irrigation schedule 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 increase on relative water content, leaf area, stomatal conductance (gS), and net CO2 assimilation rate was observed with scions grafted on ‘Beaufort’. In addition, this rootstock had a significantly longer total root system (118.6 m) compared with ‘Shield’ (94.9 m) and the self-grafted control (104.2 m). Furthermore, 76.4% 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 (φPSII). At normal irrigation there were no differences among the rootstock treatments; however, at reduced irrigation ‘Beaufort’ had significantly higher φPSII than both ‘Shield’ and the self-grafted control. These results may explain some of the improved production and water use efficiency observed in field trials using ‘Beaufort’ rootstock, and data secured may allow for better screening of rootstocks for improved water use efficiency in the future.
Tomato (Solanum lycopersicum L.) is a warm-season, cold-sensitive crop that shows slower growth and development at temperatures below 18 °C. Improving suboptimal temperature tolerance would allow earlier planting of field-grown tomato and a reduction in energy inputs for heating greenhouses. Grafting tomato onto high-altitude Solanum habrochaites (S. Knapp and D.M. Spooner) accessions has proven effective at improving scion suboptimal temperature tolerance in limited experiments. This study was conducted to determine whether commercially available tomato rootstocks with differing parental backgrounds and root system morphologies can improve the tolerance of scion plants to suboptimal temperature. Two controlled environment growth chambers were used 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 nongrafted and self-grafted control as well as scion grafted on ‘Multifort’ (S. lycopersicum × S. habrochaites), ‘Shield’ (S. lycopersicum), and S. habrochaites LA1777 rootstocks. Plants were grown for 10 days in 3.8 L plastic containers filled with a mixture of calcined clay and sand. ‘Multifort’ rootstock significantly reduced the amount of cold-induced stress as observed by larger leaf area and higher levels of CO2 assimilation and photosystem II quantum efficiency. ‘Multifort’ had significantly longer roots, having 42% to 56% more fine root (diameter less than 0.5 mm) length compared with the other nongrafted and grafted treatments. Leaf starch concentration was significantly lower in ‘Multifort’-grafted plants at suboptimal temperatures compared with the self-grafted and nongrafted controls and the ‘Shield’-grafted plants at the same temperature. The ability for ‘Multifort’ to maintain root growth at suboptimal temperatures may improve root system sink strength, thereby promoting movement of photosynthate from leaf to root even under cold conditions. This work demonstrates that a commercially available rootstock can be used to improve suboptimal temperature tolerance in cold-sensitive ‘Moneymaker’ scions.
Hemp (Cannabis sativa L.) research and commercial production has recently experienced a global revival motivated by passage of laws reversing long-standing prohibitions and by expansion in markets. Collaborative research has been initiated in response to renewed interest in hemp production, such as the American Society for Horticultural Science Hemp Research and Extension Professional Interest Group (ASHS Hemp). Collaborators new to this crop have identified a lack of standard definitions, descriptions, and procedures for cohesive study specific to hemp production. Standards are necessary for synthesis of data gathered across research and industry programs. ASHS Hemp convened a workshop of hemp researchers and industry representatives to establish consensus on a minimum set of standards for research data and industry assessments. The resulting morphology and physiology standards developed at the workshop are presented here with a focus on plant height, flowering time, and crop quality. Plant height was defined as the vertical distance between the root crown at the soil surface and the stem node (or tip) of the apical meristem of the tallest branch. Plant height was importantly distinguished from stem length and canopy height, which may differ based on pruning and management of the plant. Flowering time was defined to indicate date of initiation of inflorescence development as the earliest day terminal flowering clusters appear visually. Flowering time was distinguished from solitary flowering behavior and floral maturity. Crop quality was determined to be a feature that should be established first by industry based on market standards and then subsequently adopted by researchers targeting outcomes in specific areas. A standard moisture content for dry flower, seed, and straw must be established. A moisture content of 10% to 12% was identified as a current standard for floral yield, whereas 8% was identified as a moisture content standard for seed crops. Bast-to-hurd ratio and decortication efficiency were fiber quality metrics identified for minimum standards, and thousand seed weight, protein content, oil content, and oil composition were considered for minimum seed quality standards. The hemp research community is well positioned to standardize genomic references and establish best management practices for production targets. These efforts would be assisted by the adoption of the proposed standard definitions, descriptions, and procedures decided by consensus at the ASHS Hemp 2022 workshop.