BcLTF1 is required for full virulence.

(A) Overexpression of bcltf1 affects the formation of infection structures. Onion epidermal strips were inoculated with conidial suspensions (on the left) or non-sporulating mycelia (on the right), and incubated for 24 h in DD. Conidia and hyphae on the surface were stained with lactophenol blue whereas invasively growing hyphae remain colorless. Scale bars, 50 µm. (B) Deletion of bcltf1 impairs the capability to colonize primary leaves of P. vulgaris. Leaves of living plants were inoculated with conidial suspensions and incubated in LD. White scale bars, 1 cm; black scale bars, 2 mm. (C) Spreading lesions provoked by Δbcltf1 mutants are characterized by increased H2O2 accumulation. Primary leaves were inoculated with conidial suspensions, detached 1 to 4 dpi, and incubated for 2 h in DAB solution. Plant tissues were decolorized prior to microscopy. (D) Addition of ascorbic acid restores virulence of Δbcltf1 mutants. Conidia were suspended in GB5 (gray) or in GB5 supplemented with 5 g/l ascorbic acid (black). Mean values and standard deviations of lesion diameters were calculated from eight lesions per strain and condition at 3 dpi. Asterisks indicate significant differences compared to WT:B05.10 in each condition (p<0.001). Pictures of lesions derived from ascorbic acid-supplemented conidial suspensions were taken 3 dpi.