Identification of Fusarium oxysporum f. sp. basilici Isolated from Soil, Basil Seed, and Plants by RAPD Analysis

Wilt and crown rot of sweet basil (Ocimum basilicum), caused by Fusarium oxysporum f. sp. basilici, represents a major problem on this crop, which is grown in Italy over a large area (approximately 80 ha) under glasshouse, mainly in the Riviera Ligure (5). First reported in Russia (12), F. oxysporum f. sp. basilici has been observed in Italy (6,22), France (15), the United States (1,2,7,24), and Israel (4). Control of this pathogen is complicated by the limited availability of registered fungicides. The only partially effective compounds are benzimidazoles, which are seldom applicable even as seed dressings because of frequent residues and inadequate levels of control (5,18). Typically, basil Fusarium wilt management relies on the integration of different control measures, such as soil and substrate disinfestation, raised bench cultivation, seed dressing, and the use of antagonistic Fusarium spp. (5,18,19,20). However, considerable potential for soil contamination and reinfestation through infected seed (3,4,9,12,14) and airborne propagules (4) makes soil disinfestation only partially effective against F. oxysporum f. sp. basilici. Low efficacy of chemical control measures, the limited availability of resistant cultivars (21), and the unsatisfactory level of control sometimes offered by the commercially available formulations of biocontrol agents (9,19) boost the urgency for seed and transplant certification procedures on sweet basil. For this reason, new techniques are needed for rapid and sensitive detection of F. oxysporum f. sp. basilici and its differentiation from saprophytic and antagonistic Fusarium spp., which may be present in soil or as seed contaminants. All F. oxysporum f. sp. basilici isolates from Italy, Israel, and the United States tested so far belong to a single vegetative compatibility group (3,8). Consequently, development of molecular tools should be facilitated in the case of F. oxysporum f. sp. basilici, which appears to be a specific clone of F. oxysporum. The objective of this research was to design a reliable and rapid method for the unequivocal recognition of F. oxysporum f. sp. basilici isolated from contaminated basil seed, plants, and infested soil. We report on the use of a random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) (23,25) technique coupled to a rapid protocol for DNA extraction from cultures grown on selective medium (16) to quickly identify F. oxysporum f. sp. basilici isolated from soil, basil seed lots, and plants.