Surface Chemical Differences Between Sweetpotato Lines with Varying Levels of Resistance to the Sweetpotato Weevil

Methodology was developed for the extraction of surface components of sweetpotato (Ipomoea batatas (L.) Lam.) storage roots. Surface components of storage roots were quantitatively extracted with methylene chloride using 8-minute ultrasonication. After removal of the solvent, the extract was treated with 3 Tri Sil-Z :1 trimethylsily lim- idazol (v/v) to convert components with hydroxyl moieties to silyl ethers and then separated on a SE-54 fused silica capillary column. Distinctly different gas chromatography profiles were found between lines displaying moderate levels of resistance ('Resisto', 'Regal', 'Jewel') to the sweetpotato weevil (Cylas formicarius elgantulus (summers)) and weevil-susceptible lines ('Centennial', SC 1149-19, W-115), indicating a possible role of surface components in insect response. Chromatographic fractionation techniques were developed for separation of major components or groups of components. The results will allow subsequent bioassaying for the presence of an ovipositional stimulant(s) and other weevil behavior-modulating compounds and their chemical characterization. The sweetpotato weevil (Cylas spp.) is the single most eco- nomically important insect pest of the sweetpotato world- wide. It attacks both the plant in the field and the edible roots during storage. Cylas spp. feeds and reproduces almost ex- clusively on members of the Ipomoea genus (Cockerham et al., 1954). Some cultivars of sweetpotato have been selected that display moderate resistance to the weevil (Jones et al., 1983, 1985) and provide a potential model for studying the chemical basis for resistance. Plant breeders have often in