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The primary reason for postharvest loss is blue mold disease which is mainly caused by Penicillium expansum. Strategies for disease control greatly depend on the understanding of mechanisms of pathogen-fruit interaction. A member of the glycoside hydrolase family, β-glucosidase 1b (eglB), in P. expansum was significantly upregulated during postharvest pear infection. Glycoside hydrolases are a large group of enzymes that can degrade plant cell wall polymers. High homology was found between the glycoside hydrolase superfamily in P. expansum. Functional characterization and analysis of eglB were performed via gene knockout and complementation analysis. Although eglB deletion had no notable effect on P. expansum colony shape or microscopic morphology, it did reduce the production of fungal hyphae, thereby reducing P. expansum 's sporulation and patulin (PAT) accumulation. Moreover, the deletion of eglB (Δ eglB) reduced P. expansum pathogenicity in pears. The growth, conidia production, PAT accumulation, and pathogenicity abilities of Δ eglB were restored to that of wild-type P. expansum by complementation of eglB (Δ eglB -C). These findings indicate that eglB contributes to P. expansum 's development and pathogenicity. This research is a contribution to the identification of key effectors of fungal pathogenicity for use as targets in fruit safety strategies. • High-level eglB expression was observed during P. expansum infection. • EglB encodes a plant cell wall degrading enzyme. • eglB was functionally characterized by knockout and complementation. • ∆eglB reduces sporulation and PAT accumulation via reduced mycelial production. • eglB contributes to P. expansum virulence. [ABSTRACT FROM AUTHOR]