Sweetpotato Periderm Components Inhibit In Vitro Growth of Root Rotting Fungi

Abstract

Sweetpotato [Ipomoea batatas (L.) Lam.] periderm components were tested for their effect on four fungi that infect sweetpotato roots: Fusarium oxysporum Schlecht. f. sp. batatas (Wollenw.) Snyd. & Hans. and F. solani (Sacc.) Mart., both of which cause stem and root disease; and Lasiodiplodea theobromae (Pat.) Griffon & Maubl. and Rhizopus stolonifer (Ehr. ex Fr.) Lind., both of which cause storage root disease. Sequential extracts of `Regal' sweetpotato periderm with hexane, methanol, and 50% methanol were inhibitory to the four fungi when incorporated into potato dextrose agar medium in petri dish bioassays. The methanol and 50% methanol extracts were much more active than the hexane extract and were combined for further study. Sephadex LH-20 column chromatography of the combined extracts, followed by bioassay with F. oxysporum indicated that the most inhibitory fraction contained the least polar components of the extract. Resin glycosides isolated from `Regal' periderm inhibited F. oxysporum, but the glycosides exhibited little concentration effect and were not as active on a tissue weight basis as other components. Periderm extracts from 10 sweetpotato clones exhibited large differences in inhibitory activity in bioassays with the four fungi. The sensitivity of the fungi to inhibition by the periderm extracts suggests that periderm components may provide protection against soil pathogens, but a relationship between such components and disease resistance was not established.