First report of the Fusarium tricinctum species complex causing Fusarium head blight in wheat in Brazil

Authors: MOREIRA, G - Universidade Federal De Vicosa; MACHADO, F - Universidade Federal De Vicosa; PEREIRA, C - University Of Maringa; NEVES, D - University Of Maringa; TESSMAN, D - University Of Maringa; Ward, Todd; DEL PONTE, E - Universidade Federal De Vicosa

Submitted to: Plant Disease
Publication Type: Review Article
Publication Acceptance Date: 9/16/2019
Publication Date: 11/30/2019
Citation: Moreira, G.M., Machado, F.J., Pereira, C.B., Neves, D.L., Tessman, D.J., Ward, T.J., Del Ponte, E.M. 2019. First report of the Fusarium tricinctum species complex causing Fusarium head blight of wheat in Brazil. Plant Disease. 104(2):586. https://doi.org/10.1094/PDIS-03-19-0552-PDN.
DOI: https://doi.org/10.1094/PDIS-03-19-0552-PDN

Interpretive Summary:

Technical Abstract: Fusarium head blight (FHB) is caused by several Fusarium spp., but F. graminearum species complex (FGSC) is the most frequent worldwide, including Brazil. During surveys from 2008 to 2011, 26 kernel-borne or airborne (air above wheat canopy during flowering) were failures in a FGSC-specific multilocus genotyping assay (Del Ponte et al. 2015). Among these, eight kernel-borne strains originated from Paraná (PR) state (two municipalities), 11 airborne strains from a field at Passo Fundo municipality, Rio Grande do Sul (RS), and seven kernel-borne strains from seven municipalities in northern RS. These were subjected to amplification and sequencing of the translation elongation factor 1-alpha (EF-1a) gene (primers EF1/EF2, O’Donnell et al. 1998). Maximum parsimony and maximum likelihood-based models were used for conducting phylogenetic analyses using MEGA X (Kumar et al. 2018). Based on EF-1a data, 11 isolates were sequenced for the second largest subunit of RNA polymerase II (RPB2) (primers 5f2/7cr, O'Donnell et al. 2008). Final analyses used the two-gene dataset and sequences are GenBank (MK572748–MK572784). Three species of the F. tricinctum species complex (FTSC) were found: 15 F. avenaceum, nine FTSC 11 and two F. reticulatum (Fig. 1). While FTSC 11 and F. avenaceum were either airborne or kernel-borne, F. reticulatum was only airborne. Among PR strains, only one was FTSC 11. In RS, FTSC 11 and F. avenaceum, airborne or kernel-borne, were in similar frequency. Eighteen isolates representative of the three species were subjected to pathogenicity tests using a susceptible spring wheat cv. BR18. Two FGSC isolates, F. graminearum (CML 3066) and F. meridionale (CML 3344), were included for comparison. Fungi were grown on SNA (Spezieller Nährstoffarmer agar) for 7 days at 25 °C with a 12h photoperiod. A macroconidia suspension (1×104 macroconidia/mL) was applied uniformly on wheat heads at flowering, using a household handheld sprayer (2 mL/head). Wheat heads were covered with a plastic bag for 48 hours and remained in the greenhouse until harvest. Disease severity was assessed visually at 4 and 8 days post inoculation (dpi) in four heads per pot with three pots (replicates). The pathogenicity assay was repeated once. A multilevel linear mixed model was fitted to FHB severity data from two evaluations. Species were fixed effects and isolates and replications within each species were random effects in the model, and least square means and 95% confidence interval were estimated. All strains were pathogenic and analysis of re-isolated strains confirmed their identity. The mean FHB severity for FTSC at 4 dpi (8 dpi) ranged from 11.74% (17.2) to 82.69% (78.7) for F. avenaceum, from 32.6% (14.0) to 79.6% (46.2) for F. reticulatum and from 14.1% (42.2) to 90.2% (97.8) for FTSC 11. Although species effect was not evident (P = 0.08), a few FTSC isolates behaved similarly to the highly pathogenic FGSC strains (Fig. 2). FTSC are known to prevail in cooler climates such as Canada and northern Europe (Bottalico & Perrone 2002, Gräfenhan et al. 2013). Recently, FTSC species have been found in wheat kernels from Kentucky, including a F. reticulatum, which failed to induce typical FHB symptoms (Bec et al. 2015), as well in barley grains from subtropical regions of Brazil (Piacentini et al. 2019). Further surveys should be conducted to understand whether FTSC is an emergent FHB pathogen and at which conditions. The toxigenic potential of these species should also be investigated as FTSC from elsewhere are known to produce enniatins and beauvericin, which are not under regulation in Brazil.