Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/2000
Publication Date: 5/10/2003
Citation: HARRISON JR, H.F., PETERSON, J.K., SNOOK, M.E., BOHAC, J., JACKSON, D.M. QUANTITY AND POTENTIAL BIOLOGICAL ACTIVITY OF CAFFEIC ACID IN SWEET POTATO STORAGE ROOT PERIDERM. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY. 2003. v.51(1)) p.2943-2948 Interpretive Summary: Sweetpotato roots are invaded by several fungi that cause rotting in the field and in storage after harvest. Sweetpotato varieties differ in resistance to these fungi, and losses are much lower in resistant varieties. These studies were conducted to determine the effect of defense chemicals in sweetpotato skin on four fungi that cause root rot diseases. Extracts of Regal sweetpotato skin inhibited all four fungi, but the root components that were previously shown to inhibit weed and insect growth were not as active on fungi as other components. Ten sweetpotato varieties differ in the degree that their extracts inhibited fungal growth. The most inhibitory varieties were rot resistant. The fungi varied in sensitivity to the periderm components. These studies indicate that secondary metabolites in sweetpotato roots may provide protection against some pathogenic fungi. The preliminary implication of this research is that measuring inhibitor levels may allow the rapid identification of rot resistant sweetpotato lines. Resistance is difficult to identify using conventional methods due to inconsistencies in the screening procedures. The capability to rapidly identify resistance would accelerate the development of resistant varieties. This would help reduce sweetpotato losses due to root rotting, which would be especially beneficial to sweetpotato breeders and growers. The discovery of fungicidal sweetpotato metabolites may lead to the subsequent isolation and identification of useful natural products.
Technical Abstract: Sweetpotato (Ipomoae batatas [L.] Lam.) periderm components were tested for their effect on four fungi, Fusarium oxysporum Schlecht. f. sp. batatas (Wollenw.) Snyd. & Hans. that causes wilt or stem rot, Fusarium solani (Sacc.) Mart., Lasiodiplodea theobromae (Pat.) Griffon & Maubl., and Rhizopus stolonifer (Ehr. ex Fr.) Lind, that cause storage root diseases of sweetpotato. Sequential extracts with hexane, methanol and 50% methanol from 'Regal' sweetpotato periderm were inhibitory to the four fungi when they were 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 f. sp. batatas indicated that the most inhibitory fraction contained the least polar components of the extract. Resin glycosides isolated from 'Regal' periderm inhibited F. oxysporum f. sp. batatas, but the glycosides exhibited little concentration effect and were not as active on a tissue weight basis as other components. Periderm extracts from ten 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 storage root diseases.