Skin Lignification Is Associated with Resistance to Skinning in Sweetpotato Storage Roots, Poster Board #140

Skinning, or surface abrasion in storage roots of sweetpotato [Ipomoea batatas (L.) Lam.] at harvest causes substantial losses of marketable products in storage. Since skin lignification is thought to improve skinning resistance, a greenhouse experiment was conducted to test this hypothesis and to investigate how pre-harvest chemical treatments would enhance the phenyl-propanoid pathway to improve skin toughness in sweetpotato. Beauregard (B-14) was grown in pots in the greenhouse for 4 months. Five days before harvest, plants were treated with foliar applications of ethephon, KOH and Diquat, and compared with two controls: devined and untreated. Higher skinning force and skin lignin content were observed in roots from ethephon treated plants. In contrast, skin phenolic content was lower in roots from ethephon treated plants. No difference was shown in cortex and stele phenolics contents among all treatments. No difference was observed in phenylalanine ammonia-lyase (PAL) activity among treatments. In contrast, polyphenol oxidase (PPO) activity in skin and cortex was higher in ethephon treated plants compared to control plants.  In addition, the force required to peel the skin was correlated with skin lignin content (r = 0.55) and skin PPO activity (r = 0.52). Therefore, skin-lignin production appears to contribute to skin set and skinning resistance in sweetpotato. These treatments, however, have little or no effect on the phenyl-propanoid pathway, but ethephon increases skin lignin production and enhances skinning resistance.