Abstract
A hyphal extract was obtained by methanol extraction of a hyphal cake of Rhizoctonia solani culture. The crude hyphal extension inhibitor (HE-inhibitor), which only inhibits hyphal extension, i.e., without growth inhibition, was extracted with ethyl acetate, at pH 9.5, from the aqueous hyphal extract. The HE-inhibitor was further purified by silica gel column chromatography with a solvent mixture of benzene and acetone, and then separated into HE-inhibitors I and II. HE-inhibitor I, which highly inhibited the hyphal extension, with characteristic curling of the hyphal tips, was isolated as a colorless syrup, whereas HE-inhibitor II, with weak activity, was isolated as colorless needles: nip 187°C; C, 80.38, 79.14; H, 4.36, 4.96; N, 16.10, 15.94%. HE-inhibitors I and II exhibt no antibiotic activity against various fungi, yeasts and bacteria, but inhibit the hyphal extension of Rhizoctonia solani R-44 at 0.1μg/ml and 5.0μg/ml, respectively. Their inhibitory spectra resemble that of validamycin, though both inhibitors are less active than validamycin.
