Inhibitory Effects of Miharamycin A on the Multiplication of Plant Viruses and the Symptom Development

Abstract

Miharamycin A, a new antibiotic isolated from cultures of Streptomyces miharaensis nov. sp., has a control effect on rice blast disease. It was also found to have a highly inhibitory effect on plant viruses.
This antibiotic inhibited TMV-local lesion formation on detached Nicotiana glutinosa leaves above 90 percent at 2.5μg/ml, and on the intact leaves 85 percent at 5μg/ml, causing no chemical injury on leaves. It also inhibited CMV (Yellow strain)-local lesion formation on intact Nicotiana glutinosa and Chenopodium amaranticolor leaves 80-99 percent at 10μg/ml. Five μg/ml of Miharamycin A almost completely inhibited TMV multiplication in tobacco leaf discs floated for 2 days on its solution. When floated for 8 days, its inhibition value reached 70 percent even at 0.25μg/ml.
Moreover, when sprayed on inoculated tobacco plants 4 times, this antibiotic inhibited the rate of tobacco mosaic virus infection by more than 70 percent at 20μg/ml, and prolonged the incubation period more than 20 days compared with control plants. In the case of PVX-Nicotiana glutinosa plants, Miharamycin A inhibited the infection 50 percent at the same concentration. When applied to rice plant by dipping roots with 10μg/ml for 40 hours, or 5μg/ml for 80 hours, this antibiotic inhibited the rice stripe virus infection by 70-80 percent.
Miharamycin A caused a chemical iniury on developed leaves at above 10μg/ml, but newly developed leaves were not injured, and the plants grew normally.