Figure 3.

Deletion of NPS6 in F. graminearum Leads to a Reduction in Virulence to Wheat.

(A) Symptom development of wheat spikes in cv Norm point-inoculated with wild-type and Δnps6 strains (Fgnps6-3-2 and Fgnps6G1-2) of F. graminearum shown at 6 d (top panel) and 14 d (bottom panel) after inoculation. The mock control was inoculated with water. Arrows in the top panel indicate inoculation points. The middle panel shows close-up views of the spikelets to which inoculum was applied (i.e., eighth from the bottom), 5 d after inoculation. Left, wild type; middle, Δnps6; right, mock. Note that the spikelets inoculated with the wild-type strain are completely bleached, whereas disease is localized in those inoculated with the Δnps6 strain. In general, wheat spikes infected by Δnps6 strains developed symptoms slowly, compared with those infected by the wild-type strain, although some variation was observed among those challenged by the Δnps6 strains.

(B) Top panel, wheat spikes infected by the wild-type (top row, left three) or Δnps6 (bottom row) strains of F. graminearum, 20 d after inoculation. The mock control was inoculated with water. Bottom panel, kernels from the spikes shown in the top panel. The positions of the kernels correspond to the original positions on the spikes in the top panel. Generally, kernels in spikes infected by the wild-type strain were more severely damaged than those in spikes infected by the Δnps6 strains. Note also that most awns on the wheat heads inoculated with the wild-type strain were bent downward, whereas most of the upper awns on the heads inoculated with the mutant strains were still pointing upward, as on the mock-inoculated heads.