The 2011 ASHS Annual Conference

Pre-harvest foliar application of ethephon has been suggested to set the skin of sweetpotato storage roots and reduce skinning at harvest. Therefore, the objective of this study was to determine the association of ethephon with skinning incidence and with the activation of the lignin pathway as a way to toughen the skin. Ethephon was applied 1, 3 and 7 days before harvest (dbh) at rates of 4.4oz/ac, 8.8oz/ac, 17.6oz/ac, and 26.4oz/ac. Ethephon treatments were devined the day of harvest. Control treatments consisted in devining the plants 1, 3 and 7 dbh.  Skinning incidence ranged between one and 11 skins (wounds) per root. Skinning was the same among ethephon rates and controls at each application time. However, devining or applying ethephon 3 and 7dbh reduced skinning incidence to 3 skins per root in comparison to 1dbh (5.4 skins per root). Since phenolic compounds are the precursors of lignin for skin lignification, samples of storage roots were analyzed for phenolic content right after harvest. Phenolic content, as chlorogenic acid equivalents, was the same in the skin for all treatments and ranged between 9 and 14 mg/g FW. In contrast, the average phenolic content in the cortex and stele of untreated roots were 0.75 mg/g FW and 0.43 mg/g FW respectively. Ethephon applications increased phenolic content between 25% and 146% depending on ethephon rate and tissue. Although ethephon is applied to the foliage, these results suggest that somehow it activates the phenolic/lignin pathway in the roots which may be contributing to skin set and skinning resistance.