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ARS Home » Midwest Area » Peoria, Illinois » National Center for Agricultural Utilization Research » Mycotoxin Prevention and Applied Microbiology Research » Research » Publications at this Location » Publication #323956
Title: Fusarium agapanthi sp. nov, a novel bikaverin and fusarubin-producing leaf and stem spot pathogen of Agapanthus praecox (African lily) from Australia and Italy

Author
item EDWARDS, JACQUELINE - La Trobe University
item AUER, DESMOND - La Trobe University
item DE ALWIS, SRI-KANTHI - La Trobe University
item SUMMERELL, BRETT - Royal Botanical Gardens
item AOKI, TAKAYUKI - National Institute Of Agrobiological Sciences (NIAS)
item Proctor, Robert
item Busman, Mark
item O Donnell, Kerry

Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2016
Publication Date: 1/20/2017
Citation: Edwards, J., Auer, D., de Alwis, S.-K., Summerell, B., Aoki, T., Proctor, R.H., Busman, M., O'Donnell, K. 2017. Fusarium agapanthi sp. nov, a novel bikaverin and fusarubin-producing leaf and stem spot pathogen of Agapanthus praecox (African lily) from Australia and Italy. Mycologia. 108(5):981-992.

Interpretive Summary: This multifaceted study reports on the discovery, characterization, and formal description of a novel fungus that is pathogenic to the popular and economically important horticultural plant, African lily (Agapanthus praecox). The novel species of the filamentous fungus Fusarium was isolated from heavily infected plants in Saluzzo, Italy in 1999 and from diseased tissue from the same host exhibiting leaf rot and spot symptoms in the Royal Botanic Gardens, Melbourne, Australia in 2010. The latter plants either died or were removed from the garden because they were so severely diseased. Koch’s postulates were completed on dwarf blue and large white-flowering varieties of A. praecox, where two isolates of F. agapanthi were able to produce slowly spreading necrotic lesions when inoculated onto leaves and flower stems. Genetic analyses of DNA sequence data from several genes indicated that the pathogen represented a novel species, which was characterized morphologically and described as F. agapanthi. Whole genome DNA sequence data and culture extracts were analyzed to assess whether this novel pathogen could produce toxic secondary metabolites. As predicted by the presence of intact bikaverin and fusarubin biosynthetic gene clusters in their genomes, isolates of F. agapanthi were able to produce these two red pigments on solid cultures. However, due to the presence of truncated secondary metabolite biosynthetic genes and gene clusters for several toxins (e.g., enniatin, equisetin and fumonisin), these mycotoxins were not detected in extracts of the solid cultures. These findings are important because they provide plant disease specialists and quarantine officials with molecular tools for the early detection and identification of this pathogen, thereby minimizing the threat of its introduction and spread.

Technical Abstract: This study was conducted to characterize a novel Fusarium species that caused leaf and stem spot on Agapanthus praecox (Agapanthus, African lily) in northern Italy and leaf rot and spot on the same host in Melbourne, Australia. Formally described as Fusarium agapanthi, this pathogen was analyzed using phenotypic, phytopathogenic, secondary metabolite, molecular phylogenetic and genomic data. Five strains were characterized, including one isolated in 1999 from symptomatic A. praecox in Saluzzo, Italy, and four in 2010 from diseased leaf tissue from the same host exhibiting leaf rot and spot symptoms in the Melbourne Gardens, Royal Botanic Gardens Victoria, Australia. Maximum parsimony and maximum likelihood molecular phylogenetic analyses of portions of six individual genes and the combined dataset all strongly supported F. agapanthi either as the earliest diverging genealogically exclusive lineage in the American Clade of the F. fujikuroi species complex, or alternatively a novel monotypic lineage sister to the American Clade. Koch’s postulates were completed on dwarf blue- and large white-flowering varieties of A. praecox, where two isolates of F. agapanthi produced slowly spreading necrotic lesions when inoculated onto leaves and flower stems. Fusarium agapanthi is distinguished from other fusaria by the production of densely branched aerial conidiophores with polyphialides throughout the aerial mycelium on synthetic nutrient-poor agar. BLASTn searches of the F. agapanthi NRRL 31653 and NRRL 54464 (5 VPRI 41787) genome sequences were conducted to predict sexual reproductive mode and mycotoxin potential. Results indicated that they possessed MAT1-2 and MAT1-1 idiomorphs, respectively, indicating that this species might be heterothallic. Furthermore, based on the presence of homologs of the bikaverin and fusarubin biosynthetic gene clusters in the F. agapanthi genomes, liquid chromatography-mass spectrometry analysis was conducted and confirmed production of these secondary metabolites in rice and corn kernel cultures of the fungus.