Baseline sensitivity and bioactivity of tetramycin against Sclerotium rolfsii isolates in Huanghuai peanut-growing region of China

Peanut stem rot caused by Sclerotium rolfsii is a serious soil-borne disease and poses a threat to the peanut production. The antibiotic fungicide tetramycin has a broad antifungal spectrum against multiple pathogens and possess low environmental risks. In current study, a total of 250 isolates collected from Huanghuai peanut-growing region of China (Henan, Shandong and Hebei Province) were used to establish the baseline sensitivity of S. rolfsii to tetramycin. The baseline sensitivity curve was unimodal and distributed from 0.01 to 0.36 mg/L, with a mean EC50 (50% effective concentration) value of 0.11 ± 0.06 mg/L. Tetramycin also had strong inhibitory activity on the formation and germination of sclerotia. There was no significant correlation of S. rolfsii sensitivity to tetramycin and other commonly used SDHI (succinate dehydrogenase inhibitor), QoI (quinone outside respiration inhibitor) and DMI (demethylation inhibitor) fungicides. Moreover, tetramycin significantly increased the cell membrane permeability and reduced the oxalate acid content. Greenhouse experiments showed that tetramycin has both protective and curative efficacy against S. rolfsii, while protective efficacy was higher than curative efficacy. Anyhow, the bioactivity of tetramycin is similar (curative efficacy) or higher (protective efficacy) than the control fungicide validamycin. In terms of application method, root drench may be more suitable for tetramycin than spraying, because root drench of tetramycin obtained a higher efficacy. These results indicated that tetramycin may be a potential alternative fungicide for the efficient control of peanut stem rot.