Biomolecular Characterization of Fusarium oxysporum Strains Isolated on Lettuce, Lamb’s Lettuce and Rocket Seeds

The species Fusarium oxysporum is ubiquitous and cosmopolitan and comprises several specialized forms, adapted to a specific host and known as formae speciales, that cause deterioration and root rot in more than one hundred species of plants. Diseases of horticultural crops caused by this fungus are very frequent and lead to severe economical losses. The seed is considered to be the main factor involved in long-distance spread of the pathogen. Recently infections ascribed to F. oxysporum f. sp. raphani have been reported on rocket (Eruca sativa) and wild rocket (Diplotaxis spp) plants in Italy, while infections ascribed to F. oxysporum f. sp. conglutinans have been reported on Lamb’s Lettuce (Valerianella olitoria). Moreover F. oxysporum f.sp lactucae has been included in the EPPO alert list (EPPO RS 2009/179), as a agent of lettuce (Lactuca sativa) and lamb’s lettuce (Valerianella locusta) wilt. ENSE, the Italian national institute involved in seed inspection, increased its efforts in order to limit the spread of F. oxysporum f.sp lactucae in pathogen-free areas. An exact identification of causative agents it’s crucial for seed health evaluation and for the management of this problem. Different formae speciales can be distinguished by vegetative compatibility grouping analysis or on the basis of pathogenicity tests on differential hosts. However a rapid and effective identification for these organisms with these methods is difficult. In the present work we propose a molecular procedure for an accurate identification of these pathogens on seeds lots. Lettuce, lamb’s lettuce and rocket seeds were screened on PDA agar plates in order to isolate all Fusarium strains. Isolates morphologically resembling F. oxysporum were identified by Translation Elongation Factor 1-alpha (TEF) gene sequencing. Strains belonging to different formae speciales were identified with sequence specific primers.