Recent Outbreak of Fusarium Wilt of Basil in Florida

Symptoms of wilt, leaf chlorosis, leaf drop, and shoot and plant death were observed in commercial fields of basil (Ocimmum basilicum L.). Disease incidence ranged from 10 to 80% among individual fields. Initial isolations from infected stem tissue were made on water agar amended with streptomycin sulfate. Single-spore isolates transferred onto corn leaf agar were identified as Fusarium oxysporum Schlechtend.:Fr. f. sp. basilicum Dzidzariya. Pathogenicity tests were performed on 10-cm-tall basil plants, cv. Siam Queen, for three Florida isolates and one Massachusetts isolate. An inoculum concentration of 1 × 10⁶ conidia per ml was applied to soil around the roots. Symptoms of wilt, external stem discoloration, and death of basil occurred after 14 days, and F. oxysporum f. sp. basilicum was reisolated from plants inoculated with all four isolates. Controls were disease-free. Identification of the isolates as F. oxysporum f. sp. basilicum was done with a set of DNA primers developed by Pan and Wick (2) for a 0.7-kb DNA fragment unique to this pathogen. This report confirms the existence of F. oxysporum f. sp. basilicum in Florida (1), and identifies this disease as a potential threat to commercial basil production. References: (1) S. A. Alfieri et al. Diseases and Disorders of Plants in Florida. Bull. No. 14. Fla. Dept. Agric. Consumer Serv., 1993. (2) Z. Pan and R. L. Wick. Phytopathology 85:1559, 1995.