Fusarium oxysporum f. sp. radicis-vanillae is the causal agent of root and stem rot of vanilla
2016
Root and
stem rot(RSR) is a very detrimental disease of vanilla worldwide.
Fusarium oxysporumis frequently associated with the disease but other
Fusariumspecies are also reported. In this
international study, 52 vanilla plots were surveyed in three of the most important vanilla producing countries (Madagascar, Reunion Island and French Polynesia) in order to determine the aetiology of RSR disease. Subsets from the 377 single-spored
Fusariumisolates recovered from rotten roots and stems in the surveys were characterized by molecular genotyping (EF1α and IGS gene sequences) and pathogenicity assays on
Vanilla planifoliaand V. ×tahitensis, the two commercially grown vanilla species.
Fusarium oxysporumwas shown to be the principal species responsible for the disease, representing 79% of the isolates recovered from the RSR tissues, 40% of which induced severe symptoms on inoculated
plantlets.
Fusarium oxysporumisolates were highly polyphyletic regardless of geographic origin or pathogenicity.
Fusarium solani, found in 15% of the samples and inducing only mild symptoms on
plantlets, was considered a secondary pathogen of vanilla. Three additional
Fusariumspecies were occasionally isolated in the study (F. proliferatum, F. concentricum and F.
mangiferae) but were nonpathogenic. Histopathological preparations observed in wide field and multiphoton microscopy showed that F. oxysporum penetrated the
root hairregion of roots, then invaded the cortical cells where it induced necrosis in both V. planifolia and V. ×tahitensis. The hyphae never invaded the root vascular system up to 9 days post-inoculation. As a whole, the data demonstrated that RSR of vanilla is present worldwide and that its causal agent should be named F. oxysporum f. sp. radicis-vanillae. (Resume d'auteur)
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