Cold Temperature Delays Wound Healing in Postharvest Sugarbeet Roots

Storage temperature affects the rate and extent of wound-healing in a number of root and tuber crops. The effect of storage temperature on wound-healing in sugarbeet (Beta vulgaris L.) roots, however, is largely unknown. Wound-healing of sugarbeet roots was investigated using surface-abraded roots stored at 6 and 12 degrees C for 28 days. Surface abrasions are common injuries of stored roots, and the storage temperatures used are typical of freshly harvested or rapidly cooled roots. Transpiration rate from the wounded surface and root weight loss were used to quantify wound healing. At 12 degrees C, transpiration rate from the wounded surface declined within 14 days and wounded roots lost weight at a rate similar to unwounded controls. At 6 degrees C, transpiration rate from the wounded surface did not decline in the 28 days after injury, and wounded roots lost 44% more weight than controls after 28 days storage. Melanin formation, lignification, and suberization occurred more rapidly at 12 degrees C than at 6 degrees C, and a continuous layer of lignified and suberized cells developed at 12 degrees C, but not at 6 degrees C. Examination of enzyme activities involved in melanin, lignin, and suberin formation indicated that differences in melanin formation at 6 and 12 degrees C were related to differences in polyphenol oxidase activity, although no relationships between suberin or lignin formation and phenylalanine ammonia lyase or peroxidase activity were evident. Wound-induced respiration was initially greater at 12 degrees C than at 6 degrees C. However, with continued storage, respiration rate of wounded roots declined more rapidly at 12 degrees C, and over 28 days, the increase in respiration due to injury was 52% greater in roots stored at 6 degrees C than in roots stored at 12 degrees C. The data indicate that storage at 6 degrees C severely slowed and impaired wound-healing of surface-abraded sugarbeet roots relative to roots stored at 12 degrees C and suggest that postharvest losses may be accelerated if freshly harvested roots are cooled too quickly.