Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2011
Publication Date: 6/20/2011
Citation: Smith, J.A., O Donnell, K., Mount, L.L., Shin, K., Peacock, K., Trulock, A., Spector, T., Determann, R. 2011. A novel Fusarium species causes a canker disease of the critically endangered conifer, Torreya taxifolia. Plant Disease. 95(6):633-639. Interpretive Summary: In this research, we discovered a new fungal species of Fusarium that has potential to cause canker disease in conifer trees. This research was conducted to identify and characterize the pathogen responsible for the rapid death of Florida torreya, a critically endangered conifer species. The results of analyses on fungi isolated from diseased trees suggested that a novel species of Fusarium might be the pathogen because it was isolated most frequently and because it could induce typical disease symptoms on Floridia torreya cultivated in a greenhouse. The results of this study will be useful to plant pathologists and conservationists interested in controlling this devastating disease and developing cultivars with broad based resistance to the Fusarium pathogen.
Technical Abstract: A canker disease of Florida torreya (Torreya taxifolia), here designated CDFT, has been implicated in the decline of this critically endangered species in its native range of northern Florida and southeastern Georgia. In our current surveys of eight Florida torreya sites, cankers were present on all dead trees, suggesting that a fungal pathogen might be the causal agent of CDFT. To identify the causal agent, nuclear ribosomal internal transcribed spacer region (ITS rDNA) sequences were determined for 115 fungi isolated from cankers on 46 symptomatic trees sampled at three natural sites in northern Florida. BLASTn searches of the GenBank nucleotide database, using the ITS rDNA sequences as the query, indicated that a novel Fusarium species designated Fsp-1 might be the etiological agent. Molecular phylogenetic analyses of partial translation elongation factor 1-alpha (EF-1a) and RNA polymerase second largest subunit (RPB2) gene sequences indicate that Fsp-1 represents a novel species representing one of the earliest divergences within the Gibberella clade of Fusarium. Results of pathogenicity experiments established that the seven isolates of Fsp-1 tested could induce typical canker symptoms on cultivated Florida torreya in a greenhouse. Koch’s postulates were completed by the recovery and identification of Fsp-1 from cankers of the inoculated plants.