Effects of Storage Conditions on Deterioration of Mechanically Injured Sweet Potato Tuberous Roots, Especially on Induction of Ipomeamarone.

The storage conditions under which mechanically injured sweet potato tuberous roots produce and accumulate ipomeamarone (Ip), a typical phytoalexin, were examined.<BR>Sweet potato tuberous roots were injured by scratching over half of their sides under sterilized conditions and were kept under high humidity (“Wet”: RH 85-95%, 13°C or 25°C) or low humidity (“Dry”: RH 60-70%, 13°C or 25°C) conditions for 3, 7, 14 and 21 days, and then they were divided into two portions, injured and non injured sides for chemical and physical analyses.<BR>Under high humidity conditions, no remarkable changes including darkening were observed in either portion and Ip was not detected.<BR>In contrast, under low humidity conditions, weight loss, decrease in starch value, increase in the content of polyphenols (PP), etc. were clearly observed and the alterations were more severe on the injured side. Induction of Ip occurred on the injured side. The deterioration along with the induction of Ip was markedly promoted at 25°C.<BR>Among the cultivars used in this experiment, i. e. Koganesengan, Shiroyutaka and Kokei-14, the former two were more susceptible to injury by scratching.<BR>The intact sweet potato tuberous roots kept under low humidity conditions did not lose weight appreciably, and no Ip was detected.<BR>These facts indicate that Ip induction in mechanically injured sweet potato tuberous roots was caused by subsequent storage under low humidity conditions. It is generally recognized that “wound healing” of cell layers beneath the wound surface is considerably slow and incomplete under unfavorable conditions such as low humidity. Accordingly, it is suggested that, under low humidity conditions, injury by scratching cannot be healed and continuously acts as a stress for the induction of Ip.