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Submitted to: Mycological Research
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 9/1/2005 Publication Date: 7/1/2006 Citation: Glenn, A.E. 2006. Natural variation of ascospore and conidial germination by fusarium verticillioides and other fusarium species. Mycological Research 110:211-219. Interpretive Summary: The fungus Fusarium verticillioides (sexual state known as Gibberella moniliformis) is of significant concern to the corn industry due to its production of the fumonisin mycotoxins, which cause a number of species-specific animal diseases. Microscopic, asexual spores known as conidia are produced in abundance by F. verticillioides. A single colony of the fungus can produce millions of conidia. Conidia are spread by wind, splashing water, and insects. Thus, conidia are crucial to the dispersal and survival of the fungus and may be essential for infection of corn plants. Variability in how these conidia germinate was examined in this study. Surface-germinating spores developed germ tubes and hyphae that grew along the surface of agar before penetration occurred. Invasive-germinating spores developed germ tubes that immediately penetrated into the agar. By assessing genetic inheritance, a single locus, designated SIG1 (surface vs. invasive germination), was found to control the germination patterns. Recombination data suggested SIG1 was linked to FPH1, a recently described locus necessary for producing conidia. Corn seedling blight assays indicated surface germinating strains were less virulent than invasively germinating strains. Assays also indicated that strains which did not produce any conidia could still be pathogenic. Thus, a proposal is made that conidia are not necessary for corn seedling disease development, but invasive germination may enhance the virulence of strains that do produce conidia. Technical Abstract: Two ascospore germination phenotypes were observed while collecting progeny from sexual crosses of Gibberella moniliformis (anamorph Fusarium verticillioides). Surface-germinating ascospores developed germ tubes and hyphae that grew along the surface of agar before penetration occurred. Invasive-germinating ascospores developed germ tubes that immediately penetrated into the agar. Segregation analyses indicated a single locus, designated SIG1 (surface vs. invasive germination), controlled the germination phenotypes. SIG1 also appeared to control similar germination phenotypes exhibited by conidia. Recombination data suggested SIG1 was linked (~7% recombination frequency) to FPH1, a recently described locus necessary for enteroblastic conidiogenesis. Corn seedling blight assays indicated surface germinating strains were less virulent than invasively germinating strains. Assays also indicated pathogenicity segregated independently of the FPH1 locus. A proposal is made that conidia are not necessary for corn seedling disease development, but invasive germination may enhance the virulence of conidiating strains. |
