Low and high-temperature effects on sweetpotato storage root initiation and early transplant establishment

Temperature is considered as a major environmental factor upon which the storage behavior of sweetpotatoes depends. To quantify shoot and root vigor responses during sweetpotato early transplant establishment, an experiment was conducted using sunlit environmental growth chambers at three day/night temperatures, 22/14 (low), 30/22 (optimum), 38/30 °C (high). Ten sweetpotato cultivars were transplanted in pots for 20 days and several shoot and root morphological and physiological traits were assessed. Sweetpotato cultivars varied significantly for many traits measured particularly root components. High and low temperatures significantly decreased the production of storage root number. Low temperature caused a marked decrease in vine length, node number, leaf area, total biomass, and net photosynthesis causing 95, 70, 78, 66, and 36% reduction compared to the optimum temperature. At high temperature, average leaf area was seven times more than optimum indicating strong temperature effects on leaf number, size, and leaf area development. Principal component analysis was used to classify sweetpotato cultivars to low and high-temperature tolerant, intermediate, and sensitive groups. The sweetpotato cultivars O'henry and Bonita were identified as tolerant, Evangeline, B14, Vardaman, and Covington as intermediate tolerant, and NC05198 and Travis as sensitive to both low and high temperatures. A poor correlation was observed between low and high temperature response indices indicating that cold and heat tolerance mechanisms are different and the selection has to be made independently in developing tolerance to low and high temperatures. The identified low and high temperature tolerant cultivars and their associated morpho-physiological characteristics may be useful for breeders to develop new cultivars that could withstand variable temperatures projected to occur in future climates aiming to increase storage root yield.