Preliminary Study of Main Pathogenicity Factors and Metabolites of Wilsonomyces carpophilus

Shot-hole disease caused by Wilsonomyces carpophilus poses a significant threat to stone fruit species, including wild apricot (Prunus armeniaca L.). This study investigated pathogenic factors (cell wall-degrading enzymes and toxins) and metabolites produced by a highly pathogenic strain (CFCC 71544) and a weakly pathogenic strain (CFCC 71543) of W. carpophilus during infection of P. armeniaca (in planta conditions). Analysis using the 3,5-dinitrosalicylic acid colorimetric method revealed that polygalacturonase (CFCC 71544: 1367.02 U/g; CFCC 71543: 1264.00 U/g) and polymethylgalacturonase (CFCC 71544: 1898.71 U·g−1; CFCC 71543: 1762.21 U·g−1) were the most active cell wall-degrading enzymes, with higher activities observed in the highly pathogenic strain (CFCC 71544). Crude toxins from CFCC 71543 induced leaf lesions averaging 41.91 mm2 and retained activity after exposure to 121 °C and UV treatment. Non-protein fractions of the toxins caused significantly larger lesions than protein fractions (15.93 mm2 vs. 5.56 mm2, respectively). Building on these in planta findings, we further characterized toxin properties under controlled laboratory conditions (in vitro). Optimal toxin production conditions were identified in Richard culture medium at pH 4, under a 12 h light/dark cycle, shaken for 12 days at 25 °C. Untargeted metabolomics identified 3244 compounds and 977 differential metabolites among mycelia, crude toxins, and the residual aqueous phase after organic solvent extraction; these metabolites were predominantly amino acids and derivatives and organic acids. These findings indicate that the main pathogenic factors of W. carpophilus are highly active polygalacturonase and heat/UV-stable, water-soluble, non-protein toxins, providing a theoretical basis for shot-hole disease prevention and control.