Fusarium equiseti as an Emerging Foliar Pathogen of Lettuce in Greece: Identification and Development of a Real-Time PCR for Quantification of Inoculum in Soil Samples

Lettuce is the most commonly cultivated leafy vegetable in Greece, available in the market throughout the year. In this study, an emerging foliar disease observed in commercial farms has been associated to the pathogen Fusarium equiseti, a member of the Fusarium incarnatum-equiseti species complex (FIESC). Thirty F. equiseti isolates obtained from symptomatic lettuce plants were identified on the basis of morphology and evaluated for their pathogenicity. The isolates were further characterized using amplification and sequence analysis of the internal transcribed region (ITS-rDNA), and of the translation elongation factor 1-alpha (TEF1-a), calmodulin (CAM), beta-tubulin (Bt), and small subunit (SSU) genes. Moreover, a novel RT-qPCR assay was developed, designing a primer pair and a probe based on the TEF1-a sequences. This assay showed high specificity, amplifying F. equiseti DNA samples, while no amplification product was observed from samples of other common soilborne fungi. The generated RT-qPCR assay could be a useful tool for the detection and quantification of F. equiseti in soil samples deriving from fields cultivated with lettuce and other leafy vegetables, hosts of this specific pathogen.