Archivio Journal of Plant Pathology

Abstract:

During October 2014, in a nursery of Vallecrosia (Imperia province, Northern Italy), 2,000 plants of M. zeilmanniana showed symptoms of a stem rot that started from the collar. As the disease progressed, stems dried and eventually collapsed. In addition, the roots were rotted. A fungus was isolated from symptomatic stem tissues. On carnation leaf agar (CLA), isolates produced short monophialides with unicellular, oval to elliptical microconidia measuring 6.1-8.5 × 2.3-3.2 (mean 7.2 × 2.8) μm, and chlamydospores and macroconidia. The first were rough walled, intercalary, singles or in pairs or clumps and measured 6-9 μm in diameter. Macroconidia were slightly falcate, septate, measured 31.4- 56.8×2.8-4.0 (mean: 42.7×3.5) μm and were characterized by a foot-shaped basal cell and a short apical cell. Such characteristics are typical of Fusarium oxysporum (Leslie and Summerell, 2006). DNA was extracted from a single-spore culture (isolate DB14OTT12M1). The elongation factor 1 alpha gene (EF1α) was amplified using primers EF1/EF2 (O'Donnell et al., 1998), obtaining a 413 bp amplicon (GenBank Accession No. KT183486). BLASTn analysis showed a 99% homology with the sequence of F. oxysporum JF740824. Furthermore, the amplification of IGS region with the primers CNS1 and CNL12 and a multialignment of both primers with several formae speciales of F. oxysporum listed in Genbank permitted to include the isolate from M. zeilmanniana into the F. oxysporum f. sp. opuntiarum clade. Symptoms of the disease were reproduced on three healthy plants of M. zeilmanniana artificially inoculated following the method described by Talgø and Stensvand (2013). F. oxysporum was constantly reisolated from inoculated stems. Controls remained symptomless. This is the first report of F. oxysporum f. sp. opuntiarum on M. zeilmanniana in Italy, and potentially in Europe.