Vine Removal Prior to Harvest, and Curing Duration and Temperature Affect the Incidence and Severity of Internal Necrosis in ‘Covington’ Sweetpotato

Abstract

Internal necrosis (IN) is a physiological disorder that affects Covington, the most commonly grown sweetpotato (Ipomoea batatas) cultivar in North Carolina. Because IN affects the quality of sweetpotato storage roots, studies have been conducted since the first report of IN in 2006. Field studies (three in 2016 and two in 2017) were conducted to evaluate preharvest and postharvest treatments on the occurrence of IN in ‘Covington’ storage roots. Four preharvest treatments consisted of combinations of high chlorine or minimal chlorine potash fertilizer and mowing vs. not mowing before harvest. For postharvest treatments, 30 storage roots were obtained at harvest from each preharvest treatment plot and immediately cured in 75 and 85 °F rooms for a duration of 0.5, 1, 2, 3, and 5 weeks in 2016, and 0.5, 1, and 2 weeks in 2017. Shorter curing durations (0.5 and 1 week) coincided with industry recommendations while longer durations mimicked the challenges that some commercial facilities face when cooling down temperatures of rooms after curing is supposed to be concluded. Once curing temperature and curing duration treatments were completed, roots were placed in a 58 °F storage room at 85% relative humidity until cut. A control comparison was included in which harvested roots were placed in a 58 °F storage room (no curing) immediately after harvest. The storage roots from all temperature treatments were then cut 49 to 80 days after harvest, and incidence and severity of IN visually rated. Preharvest potash fertilizer treatments had minimal or no effect on occurrence of IN. However, mowing vines before harvest in several studies reduced IN incidence when roots were cured for more than 0.5 week at temperatures of at least 75 °F. Lower temperature (75 vs. 85 °F) and shorter curing duration (0.5 vs. 1, 2, 3, or 5 weeks) resulted in reduced IN occurrence in ‘Covington’ sweetpotato.