Multiple Defense Functions of Sweetpotato Resin Glycosides

Abstract

Sweetpotato resin glycosides were purified by HPLC methods. Most allelopathic potential could be explained by these compounds. Fifty percent inhibition (I50) of seed germination was obtained for redroot pigweed at 160 ppm, for velvetleaf at 13 ppm and for prosomillet at 11 ppm. Seed of the congeneric species I. purpurea was not sensitive. Growth of yellow nutsedge was drastically reduced, the I50 for shoot growth was 30 ppm, for number of roots 36 ppm, and for total root length 19 ppm. The glycosides accounted for approximately half of the total fungicidal activity of all extract fractions when tested on Fusarium oxysporum pv. batatae. At 2 mg per ml, the glycosides inhibited hyphal growth by 31%. This concentration is less than 10% of the glycoside concentration in dry periderm tissue of `Regal'. The purified glycosides were incorporated into a meridic diet for diamondback moth larvae. All observed antibiosis was caused by the glycosides; the LD50 was 7.2 mg per ml diet. At that concentration the surviving larvae showed a weight decrease of 46%.