Abstract: An optimal protein extraction method, as much as possible to obtain high-quality extracellular proteins of Valsa mali, is helpful to thoroughly analyze the proteomics and pathogenesis of the pathogen. In this study, the three methods freeze drying system/dialysis, DOC-10%TCA precipitation and ammonium sulfate precipitation were used to extract the extracellular proteins of Valsa mali, respectively. Then the optimal concentration of ammonium sulfate needed to be screened. The proteins extracted by the three methods were quantified and separated separately through Bradford and SDS-PAGE, and then extracellular proteins extracted from pathogenicity of different isolates were also compared with SDS-PAGE. The results showed that the content and distinguishability of protein sample extracted by 70% ammonium sulfate was optimal, and four protein lanes are significantly different in the SDS-PAGE electrophoresis patterns of different isolates. So this method is the most suitable for extracting extracellular protein sample to analyse the difference of Valsa mali protein.

Key words: Valsa mali, Ammonium sulfate precipitation, Protein quantification , DS-PAGE, Different proteins