Head Blight Gradients Caused by Gibberella zeae from Area Sources of Inoculum in Wheat Field Plots

Abstract

The spread of Fusarium head blight of wheat from a small area inoculum source was examined in wheat plots (100, 625, or 2,500 m(2)) inoculated in the center with Gibberella zeae-colonized corn kernels or macro-conidia sprayed on heads at anthesis. With the first inoculation method, disease foci were produced from ascospores released from perithecia formed on inoculated kernels. With the second inoculation method, disease foci were produced by macroconidia directly applied to the heads. Some plots were misted during anthesis. Plots were divided into grids, and disease incidence on spikelets and seeds was assessed at the grid intersections. Isopath contour maps were constructed using an interpolation procedure based on a weighted least squares method. Disease gradients were constructed from the isopath contours in the direction parallel to average nightly wind vectors using an exponential model. This study was conducted over a 3-year period at two sites: one in Quebec and one in Ontario. Both inoculation methods resulted in a discrete, primary focus of head blight in each plot, with one or two smaller secondary foci in some plots. The highest incidence of disease on spikelets or seed was commonly displaced somewhat from the inoculum source, usually downwind. The gradient slopes of seed and spikelet infection ranged from -0.10 to -0.43 m(1) in plots with ascospore inoculum and from -0.48 to -0.79 m(1) in plots inoculated with macroconidia. Seed infection declined to 10% of the maximum within 5 to 22 m from the focal center in asco-spore-inoculated plots, and within 5 m in a macroconidia-inoculated plot. Gradients were usually steeper upwind compared with downwind of the inoculum source. In misted plots, incidence of disease was higher and more diffuse than in nonirrigated plots. Based on gradients and dispersal patterns, disease foci in plots inoculated with G. zeae-colonized corn kernels probably arose from airborne ascospores rather than from splash-borne macroconidia and were the result of infection events that occurred over a short period of time. Comparison of conidial- and ascospore-derived disease gradients indicated a lack of secondary infection, confirming that Fusarium head blight is primarily a monocyclic disease.

Fusarium head blight : a re-emerging disease

“…This same timing has been corroborated in other subséquent studies. Disease from small area sources of inoculum (1 m 2 ) are asymmetrical, steeper on the upwind than downwind side of the gradient (Fernando et al 1997b). …”

Effects of Temperature and Moisture on Development of Fusarium graminearum Perithecia in Maize Stalk Residues

“…Ascospores and macroconidia are the main inocula (3,7,9) and are typically produced on the residues of the previous crop (4, 7). The fungus can survive as a saprophyte on the previous crop's residue for 2 or more years (10,11,12).…”

“…Macroconidia are produced in sporodochia and are dispersed for short distances by splashing rain (14,15,16). Ascospores mature in perithecia and are forcibly discharged into the air; they are then airborne and can travel meters to kilometers (9,17,18,19).…”

Expression and Function of Sex Pheromones and Receptors in the Homothallic AscomyceteGibberella zeae

“…zeae is a homothallic fungus, and strains originating from a single haploid nucleus can successfully complete the sexual cycle without a mating partner. This process may be advantageous for maximizing the production of ascospores, which are important as inoculum for initiating disease epidemics of wheat (17). Other species in the genus Gibberella are heterothallic, and strains of these species must cross with a strain of the opposite mating type to produce perithecia, complete meiosis, and produce ascospores.…”