Abstract
Altericidins (altericidin A, B and C), remarkably inhibited the mycelial growth of Alternaria kikuchiana in a liquid medium at low concentrations. The fifty percent inhibitory concentration (EC50) for the mycelial growth varied widely according to the initial mycelial weight. The higher the initial density, the higher the EC50. However, the ratio of EC50 (μg/ml) to the dry weight inoculum (mg/ml) was 2.8, when the initial mycelial weight ranged from 0.8 to 1.45mg (dry weight/ml), and increased in proportion to the mycelial weight (dry weight) under the conditions tested. Scanning electron micrographs showed partial swelling, rupture and exfoliation in the outer cell wall layer of conidium of A. kikuchiana when treated with various concentrations of altericidins. The conidium bursted when treated at a higher concentration of 40ppm. When the hyphae were treated with 20ppm altericidins for 6hr, some of the cells heavily shrunk, and others became empty and flattened. The leakage of cellular constituents was also observed in sporidium of Ustilago maydis treated with 20ppm altericidins for 3hr. These results suggest that altericidins act on the cell wall.
