ARS | Publication request: ARE GIBBERELLA ZEAE SEXUAL SPORES THE CRITICAL INOCULUM FOR WHEAT HEAD BLIGHT?

Submitted to: Fungal Genetics Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: March 18, 2001
Publication Date: N/A

Technical Abstract: Gibberella zeae (anamorph Fusarium graminearum) causes head blight (scab) in wheat and barley, and ear rot in corn. Since 1991, epidemics of Gibberella head blight have had disastrous effects on wheat and barley production in the Midwestern states. In addition to decreasing yields, the fungus also contaminates grain with trichothecene mycotoxins that are harmful to human and animal health. To understand and control head blight the factors and conditions that lead to epidemics must be identified. Observations in the field suggest that G. zeae sexual spores (ascospores) produced on plant debris in the soil are a primary source of inoculum for head blight epidemics. Sexual reproduction in G. zeae is controlled by a mating-type (MAT) locus that contains four genes located within 6 kb of genomic sequence. To test the role of ascospores in causing blight, we have constructed an ascospore non-producing strain by deleting the MAT locus using a transformation mediated gene replacement strategy. MAT-null strains appear indistinguishable from wild-type strains in morphology and production of asexual spores (macroconidia). In addition, MAT-null strains are similar to wild-type strains in virulence following injection of individual wheat heads with macroconidia. Experiments planned for Spring 2001 will test a MAT-null strain and the wild-type strain from which it was derived for their ability to cause head blight on wheat following application of infested maize stalk piences to the soil surface. If ascospores are the major inoculum source, then we predict that exposure of wheat heads to a MAT-null strain that cannot produce ascospores should cause less blight than exposure to an ascospore producing strain.