Wound healing, keeping quality, and compositional changes during curing and storage of sweet potatoes

California’s mild climate has led to handling and storage practices with sweet potatoes that do not necessarily provide optimum conditions for wound healing. Experiments were conducted during a four-year period with three varieties on San Joaquin Valley farms to determine whether a curing period in a warm house, such as is customary in other areas, would favor wound healing and reduce storage losses and quality changes. A two-week curing period in a warm house, with a temperature of around 85° F and high relative humidity, was compared with a similar period in a field pile, the method commonly used in California, and with direct placement in an unheated storage house. The experiments indicated that where storage of sweet potatoes for several months is economically sound, a warm-house curing period will usually reduce rot (except black rot), improve the appearance of roots, and decrease handling and sorting at the end of storage. The improvement was more consistent in the Porto Rico and Hawaiian varieties than in Yellow Jersey, which was more heavily infected with black rot. The treatments had little effect on sugar percentage, or, except toward the end of the storage period, on loss of dry weight. Anatomical studies and photomicrographs were made of changes in the natural uninjured periderm and in wound tissue on broken ends and cut sides of roots under the three methods of treatment. The natural periderm increased during the curing period in the Hawaiian and Porto Rico varieties but not in the Yellow Jersey. In all varieties the cork layer of wound tissue in roots cured in the warm house was thicker, more regular, and lighter in color than under the other treatments. Healing was similar in the two types of wounds. In the wound area on the broken ends of roots, sieve tubes and laticifers were compressed and pinched off, and vessel elements became filled with tyloses, which sometimes divided to produce across the vessel lumen a cork layer continuous with that in surrounding tissue.