Abstract

Soilborne diseases, such as tomato wilt caused by the fungus Fusarium oxysporum f. sp. lycopersici, are important biotic constraints in sustainable crop production systems. Preplant soil fumigants including methyl bromide are used extensively to protect crops from soilborne pathogens. Alternative methods for controlling soilborne diseases are desired to replace methyl bromide while maintaining high levels of disease control. Validamycin A (VMA) is an aminoglucoside antibiotic used for the control of rice sheath blight caused by Rhizoctonia solani. We found that foliar application of VMA or validoxylamine A (VAA) effectively controlled tomato wilt. VMA and VAA have no direct antifungal activity against F. oxysporum f. sp. lycopersici. Plants sprayed with VMA or VAA accumulated salicylic acid, and had elevated expression of the systemic acquired resistance (SAR) marker genes P4 (PR-1), Tag (PR-2), and NP24 (PR-5). Foliar spray of VMA also controlled bacterial wilt (caused by Ralstonia solanacearum), late blight (Phytophthora infestans) and powdery mildew (Oidium sp.) of tomato. These results suggest that VMA and VAA are plant activators. Foliar application of plant activators may be a viable alternative to soil fumigation to control soilborne diseases.