Antibacterial Activity of Validamycin A against Pseudomonas solanacearum and Its Efficacy against Tomato Bacterial Wilt.

Validamycin A (VM-A), the active ingredient of Validacin®, inhibits fungal growth by inhibiting trehalase activity. Therefore, VM-A was tested against Pseudomonas solanacearum for its efficacy in controlling tomato bacterial wilt. In media containing trehalose as the sole carbohydrate, VM-A at 50μg/ml inhibited growth of P. solanacearum to rates similar to that of the bacteria in media without carbohydrate for seven days after inoculation. VM-A also gave excellent control of tomato bacterial wilt in greenhouse pot tests, when directly injected into plant stems. In field tests, foliar sprays of VM-A at 250μg/ml five days before and two days after inoculation had reduced disease by 47.4% by four weeks after inoculation. In the tomato stem between 0 and 5cm above the soil line, the bacteria population in the non-treated plot reached 3.84×1010cfu/g fresh weight, whereas that in the VM-A (500μg/ml)-treated plot reached 2.13×109cfu/g fresh weight. Inhibition of bacteria growth by VM-A may delay the appearance of disease symptoms of tomato bacterial wilt.