Enzyme activity and hydrolytic activity of VdGAL4. (A) α-Galactosidase activity of wild-type (WT) Verticillium dahliae strain Vd080, the two VdGAL4 deletion mutant strains (ΔVdGAL4-1 and ΔVdGAL4-2 strains), and the two VdGAL4 complement mutant strains (C-ΔVdGAL4-1 and C-ΔVdGAL4-2 deletion mutant strains). (B) Structural formulas of isomaltose and melibiose and the cleavage sites of α-1,6 glycosidic bonds of VdGAL4. (C, D) VdGAL4 hydrolyses isomaltose (C) and melibiose (D); the transparent circles of all tested strains were observed by iodine-KI staining solution. (E, F) Diameter of transparent circles on water agar medium amended with isomaltose (E) and melibiose (F). The error bar represents standard error of the mean. *, P < 0.05; **, P < 0.01.