Pre-harvest Application of Ethephon Enhances Skin Lignification and Increases the Force Required to Peel Sweetpotato Storage Roots

Skinning in storage roots of sweetpotato [Ipomoea batatas (L.) Lam.] occurs during harvest and causes substantial losses in marketable products. Since there are reports that ethephon improves skinning resistance in sweetpotato, a field study was conducted to determine the association of pre-harvest application of ethephon with skinning resistance and the effect on skin lignifications. Beauregard (B-14) plants grown in the field were treated with foliar applications of ethephon or devined before harvest. Storage roots from treated plants were compared with roots from non-treated/non-devined plants (control). Root samples were taken periodically for analysis. At day 6 after treatment, all roots were harvested and cured in a chamber (29 °C and 85% RH). Roots samples were also taken after harvest and curing for analysis. Results showed that devining and ethephon treatment increased the force required to peel the root (skinning force). The skinning force in roots from ethephon treatment plants was slightly higher than devined plants. Skin lignin content had a similar pattern among treatments and was well correlated (r = 0.89) to skinning force. Skin phenolic contents were lowest in the ethephon-treated plants while untreated plants had higher phenolic contents. Our results suggest that although ethephon is applied to the foliage, it activates the production of skin lignin in the roots. Also skin lignification appears to be involved in skin toughening and skinning resistance.