Temperature moderates various plant physiological processes, in turn affecting the overall rate of development, and is utilized in controlled environment food crop production to influence product yield, quality, and to manage crop scheduling. Root crops, including spring radish (Raphanus raphanistrum subsp. sativus), currently represent a niche segment within commercial controlled environment food production. The lack of reliable cultural information has been noted as a reason producers may be hesitant to introduce new crops to their operations. To expand commercial adoption, this study aims to quantify the effect of air temperature on spring radish development, specifically determining minimum temperature (Tmin), optimum temperature (Topt), maximum temperature (Tmax), and linear temperature range. Two cultivars of spring radish, ‘Crunchy King’ and ‘Red Castle’, were grown in separate climate-controlled environmental growth chambers providing continuous target air temperatures of 8, 13, 18, 23, 28, and 33 °C, a range of 25 degrees. Samples were grown in commercial 72-cell plug trays filled with peat-based substrate and fertigated with custom ebb-and-flood systems providing 200 ppm nitrogen at every irrigation. A 16-h photoperiod was provided, with a target light intensity of 200 µmol·m2·s1. Samples were harvested 28-d after seeding and data collected, including diameter of the hypocotyl, number of mature leaves, and length of the longest leaf. A measure of relative chlorophyll concentration was recorded, and finally, fresh and dry mass of the hypocotyls and shoot tissue was measured. Results indicate that hypocotyl diameter increases linearly from Tmin at 3 °C, reaching a maximum at Topt of 23 °C. Beyond this point, diameter is reduced, with Tmax occurring at 35 °C. Hypocotyl fresh and dry mass followed similar patterns, correlating strongly with diameter. Leaf number was observed to be maximized at 18 °C, with no significant increase beyond this temperature. Leaf length was maximized at 23 °C and decreased with increasing temperature. Average daily temperature was observed to have no significant effect on relative chlorophyll concentration. Notably, we found that there was no significant difference between the two cultivars in their response to air temperature. The results of this study offer important guidance to producers interested in introducing spring radish into their operation, while maximizing crop quality and yield.
