Evaluation of bioactivity and control efficacy of tetramycin against Corynespora cassiicola.

Tetramycin is a novel polyene antibiotic that has exhibited excellent inhibitory activity against many plant pathogens. In this study, the sensitivity of Corynespora cassiicola to tetramycin was assessed in vitro using a series of 91 isolates, and its effects on hyphae and conidia were evaluated. Preventive and curative efficacies of tetramycin against Corynespora leaf spot were evaluated using detached cucumber leaves and potted cucumber plants. The control efficacy of tetramycin against the pathogen was also determined under field conditions. Measurement of baseline sensitivity suggested that the frequency distribution of tetramycin fits a unimodal curve. Among several life stages, spore germination was most severely inhibited by tetramycin, whereas mycelial growth was found to be the least sensitive. Microscopy observation revealed that tetramycin treatment leads to abnormal morphological development of C. cassiicola. Overall, tetramycin exhibited excellent curative and preventive activities against C. cassiicola on both cucumber leaves and potted cucumber plants. Furthermore, tetramycin significantly reduced the disease severity of Corynespora leaf spot in the field. The results from this study showed that tetramycin may play an important role in Corynespora leaf spot disease management and promote its introduction into fungicide-application programs.