Source: NCSU COLLEGE OF AG & LIFE SCIENCES, 9/23/20


NC State researchers have determined a postharvest treatment that significantly reduces crop loss due to internal necrosis in Covington sweetpotatoes. About 90% of North Carolina’s sweetpotatoes are of the Covington variety. This treatment will save N.C. sweetpotato producers millions of dollars.

The Covington variety of sweetpotatoes produces a high yield of fairly uniformly shaped storage roots that are delicious, nutritious and store well. However, within a few years of the variety’s commercial release, growers and consumers started noticing black spots or patches on the inside of the sweetpotatoes.

“Internal necrosis was becoming a big issue in the industry, so the Sweet Potato Commission decided we needed a task force to look at this from across the college,” said David Godwin, a third-generation sweetpotato producer who has served on the North Carolina Sweet Potato Commission in a number of roles. “When you’ve got an issue where you really don’t know what’s happening, you need to get somebody from every field and aspect of agriculture and life sciences to work on it.”

Internal necrosis is a physiological disorder, not caused by a pest or pathogen, where the sweetpotatoes develop black spots and patches on the inside of the root. These black patches are only found in the end of the root closest to where the vine was. Producers cannot tell if a root has internal necrosis without cutting into it.

According to Jonathan Schultheis, a professor and Extension specialist in the Department of Horticultural Science who led the task force, a survey of sweetpotato storage rooms in 2010 and 2011 found 90% of the storage rooms had at least some roots with internal necrosis. In most cases, less than 10% of the sweetpotatoes examined had these minimal black patches or specks. However, a few producers had more than 30% affected roots, some with more severe symptoms, making them not marketable.

By changing the curing process — a heat treatment that encourages the roots to heal cuts and abrasions and converts starch into sugar after harvesting and before storing in a cool storage room — Schultheis and the task force determined a method to greatly reduce the incidence and severity of internal necrosis in Covington sweetpotatoes.

Last month, the task force shared the solution with the scientific community in the form of a paper published in the journal HortTechnology. They shared the solution with sweetpotato producers in 2017, after the first set of experiments proved successful.

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