SUNFLOWER GERMPLASM DEVELOPMENT FOR IMPROVED INSECT AND DISEASE RESISTANCE
Location: Sunflower Research
Title: First Report of Pathogenicity of Fusarium sporotrichioides and Fusarium acuminatum on Sunflowers in the United States
Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 15, 2010
Publication Date: September 15, 2010
Citation: Mathew, F., Kirkeide, B., Gulya, T.J., Markell, S. 2010. First report of pathogenicity of Fusarium sporotrichioides and Fusarium acuminatum on sunflowers in the United States. Plant Health Progress. Available: http://www.plantmanagementnetwork.org/sub/php/brief/2010/fusarium/
Interpretive Summary: Several unidentified fungi were isolated from sunflower plants with pink discoloration of the stem interiors. After conventional and molecular methods were used to identify the fungi, a total of three species of Fusarium were found. One has been noted before on sunflowers, while the other two have not been reported on sunflower in the U.S. The latter two, however, are considered serious pests on sunflower in Russia. Thus, special care should be taken to monitor the occurrence of these Fusarium species. If they are noted to be widespread, they could pose a serious threat to U.S. sunflower production, and research to address management options would be warranted.
Widespread infection of charcoal rot (Macrophomina phaseolina (Tassi) Goid) was observed in a commercial sunflower field (Helianthus annuus L. cv. 'Pioneer 63M82') in Todd County, MN in September 2009. Stem sections of the basal portion of infected plants were harvested and dissected. In addition to spherical microsclerotia of M. phaseolina, a pink discoloration of the pith was observed. Small pieces of pink pith were surface disinfested, rinsed in sterile distilled H20, transferred on potato dextrose agar (PDA) in petri dishes and incubated for 7 d at 22-25 C under fluorescent lights with a 12-h photoperiod. Spores were harvested and streaked on 1.5% water agar and after 3 d, individual colonies transferred. Based on morphology the isolates were identified as Fusarium oxysporum Schlect. emend. Snyd. & Hans., and two other Fusarium spp., suspected to be F. sporotrichoides Ellis & Everhar. and F. acuminatum Sherb. DNA was extracted from lyophilized mycelium of the latter two Fusarium spp. using the DNeasy Plant mini kit (Qiagen, Valencia, CA) and its translation elongation factor 1-alpha (TEF1-alpha) gene region was amplified using ef1 and ef2 primers. PCR amplicons of ~700 bp were directly sequenced in both directions using the same primers, and a BLASTN search against the NCBI nucleotide database was performed using the consensus sequence generated by alignment of the forward and reverse sequences for this region. BLASTN search results confirmed the identity of F. sporotrichioides (closest match was Accession No. EU744849) and F. acuminatum (closest match was Accession No. FJ154737). Koch's postulates were performed with both pathogens in greenhouse conditions by inoculating 3-wk-old sunflower (cv. 'Pioneer 63M82') by placing mycelial agar plugs of 7-d-old cultures (PDA) on wounded stems. Necrosis was observed 10 d after inoculation with each pathogen. Plants inoculated with Fusarium sporotrichioides wilted 14 d post-inoculation. Girdling lesions developed on plants inoculated with F. acuminatum at 14 d post inoculation, but wilting was not observed by 21 d, when experiments were terminated. No symptoms were observed on control plants inoculated with sterile agar plugs. Both Fusarium spp. were re-isolated from the inoculated plants, fulfilling Koch's postulates. Fusarium wilt of sunflower was first reported in Texas in the United States, and, as in this report, the causal agent (unidentified Fusarium spp.) was recovered with M. phaseolina. Despite the occurrence of M. phaseolina, Orellana found that the Fusarium spp. was the primary etiological agent causing wilt in Texas. The repeated co-occurrence of M. phaseolina and Fusarium spp. may be important. Although the economic implications of Fusarium spp. on sunflowers are unclear in the United States, Fusarium is currently a serious economic problem on sunflower in Russia; where F. sporotrichoides and F. acuminatum have been identified as part of a Fusarium complex, with F. sporotrichoides the most aggressive of all species identified. To our knowledge, this is the first report of F. sporotrichoides and F. acuminatum causing disease on Helianthus annuus L. in the United States.