Root Carbohydrate, Organic Acids, and Phenolic Chemistry in Relation to Sweetpotato Weevil Resistance

Methanol extracts of external (outer 3 mm) and interior root tissue of four sweetpotato [Ipomoea batatas (L.) Lam.] cultivars (`Centennial', `Jewel', `Regal', and `Resisto') having different levels of susceptibility to the sweetpotato weevil [Cylas formicarius elegantulus Summer] were analyzed for simple carbohydrates (fructose, glucose, sucrose, inositol) and organic acids (malic, citric, quinic) by gas chromatography and for phenolics (caffeic acid, caffeoylquinic acids, rutin) by high-performance liquid chromatography. There were significant differences among cultivars in the concentrations of total sugars and phenolics in the external tissue (P < 0.05). In addition, the distribution of carbohydrates, organic acids, and chlorogenic acid [3-O-caffeoylquinic acid] differed between external and interior tissues. Sucrose was the major water-soluble carbohydrate in all cultivars. With the exception of malic acid, the concentration of carbohydrates, organic acids, and phenolics did not correlate with cultivar susceptibility to the sweetpotato weevil.