|Kistler, H - Corby|
Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/23/2011
Publication Date: 12/20/2011
Citation: Sarver, B.A., Ward, T.J., Gale, L.R., Broz, K.L., Kistler, H.C., Aoki, T., Nicholson, P., Carter, J., O Donnell, K. 2011. Novel fusarium head blight pathogens from Nepal and Louisiana revealed by multilocus genealogical concordance. Fungal Genetics and Biology. 48(12):1077-1152. Interpretive Summary: Fusarium head blight (FHB) has become a significant threat to the production of small grain cereals over the past 20 years in all major production areas worldwide. The present study was conducted to characterize the genetic diversity, toxin potential, and ability of five isolates of the filamentous mold Fusarium to induce FHB of wheat in a pathogenicity experiment. The isolates studied appeared to be genetically novel based on surveys of FHB of wheat in Louisiana and rice in Nepal. Results of a novel molecular diagnostic indicated that the isolates might represent novel FHB pathogens. The pathogen diagnostic also indicated that the isolates from Louisiana and Nepal might produce nivalenol and deoxynivalenol toxins, respectively, in vivo. This prediction was confirmed by analyzing wheat heads inoculated with the isolates. Further genetic analyses of the isolates, using DNA sequence data from multiple genes, indicated that they represented novel FHB pathogens. Thus, they were formally described as F. louisianense and F. nepalense using detailed morphological data. This research should benefit the efforts of plant breeders to develop wheat and rice cultivars with broad based resistance to FHB. In addition, because the molecular diagnostic was expanded to detect these novel FHB pathogens, it provides quarantine officials with the only diagnostic available for their rapid detection and accurate identification.
Technical Abstract: This study was conducted to assess evolutionary relationships, species diversity, and trichothecene toxin potential of five Fusarium graminearum complex (FGSC) isolates identified as genetically novel during prior Fusarium head blight (FHB) surveys in Nepal and Louisiana. Results of a multilocus genotyping (MLGT) assay for B-trichothecene species determination indicated these isolates might represent novel species within the FGSC. Genealogical concordance phylogenetic species recognition (GCPSR)-based phylogenetic analyses of a 12-gene dataset, comprising portions of seven loci totaling 13.1 kb of aligned DNA sequence data, provided strong support for the genealogical exclusivity of the Nepalese and Louisianan isolates. Accordingly, both species are formally recognized herein as novel FGSC species. Fusarium nepalense was resolved as the sister lineage of F. ussurianum + F. asiaticum within an Asian subclade of the FGSC. Fusarium louisianense was strongly supported as a reciprocally monophyletic sister of F. gerlachii + F. graminearum, suggesting that this subclade might be endemic to North America. Multilocus Bayesian species tree analyses augment these results and provide evidence for a distinct lineage within F. graminearum predominately from the Gulf Coast of Louisiana. As predicted by the MLGT assay, mycotoxin analyses demonstrated that F. nepalense and F. louisianense could produce 15-acetyldeoxynivalenol (15ADON) and nivalenol, respectively, in planta. In addition, both species were only able to induce mild FHB symptoms on wheat in pathogenicity experiments.