ΔBcMkk1 displayed higher virulence, increased activity of extracellular hydrolases (EHs) and more oxalic acid than ΔBcBck1 and ΔBcBmp3.

<p>(A) Pathogenicity of each strain on strawberry, pear and apple fruits, and tomato leaves. Agar plugs without fungal mycelia were used as negative controls (NCKs). Disease symptoms were photographed 60 h post inoculation (hpi). (B) Diameters of disease lesions of each strain shown in (A). Values on the bars followed by the same letter are not significantly different at <i>P</i> = 0.05. (C) Onion penetration assays of 38B1, ΔBcBck1, ΔBcMkk1 and ΔBcBmp3. Infection structures (indicated by red arrows) were stained with aniline blue 24 and 36 hpi. Bar = 20 μm. (D) Comparisons of the phosphorylation level of MAPK BcBmp1 in the Fus3/Kss1 pathway among the above strains. BcBmp1 and phosphorylated BcBmp1 proteins were detected using the p44/42 MAPK and phospho-p44/42 MAPK antibodies, respectively. The intensities of the western blotting bands were quantified with the programme IMAGE QUANT TL. The intensity of phosphorylated BcBmp1 band for each strain is relative to that of BcBmp1 band. (E) ΔBcMkk1, but not ΔBcBck1 and ΔBcBmp3, exhibited obvious degradation halo on each enzyme activity-detecting medium. Photographs were taken 3 days after inoculation (dai) for laccase detection and 5 dai for protease and peroxidase detection. (F) Activity of EHs was measured after grown in CM for 5 days. Values on the bars followed by the same letter are not significantly different at <i>P</i> = 0.05. (G) The transcription of protease, peroxidase and laccase genes in each strain. The expression level of each gene in 38B1 was referred to 1. Values on the bars followed by the same letter are not significantly different at <i>P</i> = 0.05. (H) ΔBcMkk1 produced more acidic compounds than ΔBcBck1 and ΔBcBmp3 on PDA amended with 0.05% bromothymol blue indicating acid production. (I) pH value of the 5-day-old culture supernatant of each strain grown in PDB. Values on the bars followed by the same letter are not significantly different at <i>P</i> = 0.05. (J) Comparisons of organic acid concentrations between 38B1 and ΔBcMkk1 after incubation in PDB for 5 days. Values on the bars followed by the same letter are not significantly different at <i>P</i> = 0.05.</p>