Fusarium oxysporum f. sp. radicis‐vanillae is the causal agent of root and stem rot of vanilla

Abstract

Root and stem rot (RSR) is a very detrimental disease of vanilla worldwide. Fusarium oxysporum is frequently associated with the disease but other Fusarium species 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 Fusarium isolates recovered from rotten roots and stems in the surveys were characterized by molecular genotyping (EF1α and IGS gene sequences) and pathogenicity assays on Vanilla planifolia and V. ×tahitensis, the two commercially grown vanilla species. Fusarium oxysporum was 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 oxysporum isolates 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 Fusarium species 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 hair region 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.

Characterization of Colletotrichum orchidophilum, the agent of black spot disease of vanilla

“…It has also been described as an endophytic organism, particularly in Reunion Island, where it has been identified frequently in aerial parts of V. planifolia, accounting for 37.6% of the isolates, and occurring at all the nine sites sampled (Khoyratty et al., ). Occasionally, F. proliferatum was also isolated in stem and roots in surveys of Fusarium associated with root and stem rot in Reunion Island (Koyyappurath et al., ) and in Indonesia (Pinaria, Liew, & Burgess, ), but was classified as non‐pathogenic in both studies.…”

Phylogenetic position and nucleotide diversity of Fusarium oxysporum f. sp. vanillae worldwide based on translation elongation factor 1α sequences

“…vanillae , has been shown as one of the most important diseases in this crop. It has already been detected in the main producing countries worldwide (Pinaria et al ., ; Vijayan et al ., ; Koyyappurath et al ., ), as well as in Mexico, the centre of origin and distribution of vanilla (Adame‐García et al ., ). The results of the present analyses indicate the hypothesis that vanilla‐pathogenic strains of F. oxysporum around the world constitute a single lineage and a progressive geographical dispersion can be rejected.…”

“…Only the TEF1 α gene was used for this study in order to use a wide sample of F. oxysporum f. sp. vanillae sequences from other studies (Pinaria et al ., ; Koyyappurath et al ., ) and many other well‐characterized sequences from GenBank.…”

Epidemiology of Fusarium agave wilt in Agave tequilana Weber var. azul

“…strains in different host crops, where the principal symptoms are injury to xylem vessels (Beckman 1987(Beckman , 1989Pegg 1989), or those symptoms caused by F. oxysporum f.spp. indicated as 'radicis-' in their names that induce combined vascular injury and limited destruction of the parenchyma of young roots and crown tissues (Charest et al 1984;Benhamou et al 1989;Koyyappuratha et al 2016). The severe rot symptoms in agave wilt are similar to those in the root and crown cortical tissue induced by necrotrophic soil-borne plant pathogens (MacHardy & Beckman 1981;Raaijmakers et al 2009).…”