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Pestalotiopsis guepinii is a pathogenic fungus that causes grey blight on Camellia pitardii. In this study, we investigated the enzyme activity and kinetics of these cell‐wall‐degrading enzymes (CWDEs) produced by Pestalotiopsis guepinii in both C. pitardii leaves and culture medium. Our enzyme activity experiments revealed that the activities of xylanase, pectin methyl‐galacturonase (PMG), β‐1,4‐endoglucanase (Cx), and β‐glucosidase were high in both C. pitardii leaves and culture medium. These enzymes played a significant role in the pathogenic process. However, the activity of laccase was found to be very low and had a minor impact on the pathogenic process. Furthermore, our enzyme dynamics experiments demonstrated that the optimal reaction temperature for PMG and Cx was 50°C, while for β‐glucosidase and xylanase, it was 60°C. The optimal reaction pH for Cx, β‐glucosidase, and xylanase was 5.0, whereas for PMG, it ranged from 5.0 to 6.0. This indicates that these four enzymes prefer acidic conditions. Moreover, we observed that the activities of Cx, PMG, and xylanase decreased with increasing reaction time. On the other hand, the activity of β‐glucosidase initially increased sharply and then decreased slowly. The maximum reaction rates of the four cell‐wall‐degrading enzymes were ranked as follows: xylanase > PMG > β‐glucosidase > Cx. Additionally, the affinities of these enzymes with substrates were ranked as follows: PMG < Cx < xylanase < β‐glucosidase. [ABSTRACT FROM AUTHOR]

SUMMARY: Phyllosphere‐associated microbes play a crucial role in plant–pathogen interactions while their composition and diversity are strongly influenced by drought stress. As dioecious plant species exhibited secondary dimorphism between the two sexes in response to drought stress, whether such difference will lead to sex‐specific differences in phyllosphere microbiome and associated pathogen resistance between male and female conspecifics is still unknown. In this study, we subjected female and male full siblings of a dioecious poplar species to a short period of drought treatment followed by artificial infection of a leaf pathogenic fungus. Our results showed that male plants grew better than females with or without drought stress. Female control plants had more leaf lesion area than males after pathogen infection, whereas drought stress reversed such a difference. Further correlation and in vitro toxicity tests suggested that drought‐mediated sexual differences in pathogen resistance between the two plant sexes could be attributed to the shifts in structure and function of phyllosphere‐associated microbiome rather than the amount of leaf main defensive chemicals contained in plant leaves. Supportively, the microbiome analysis through high‐throughput sequencing indicated that female phyllosphere enriched a higher abundance of ecologically beneficial microbes that serve as biological plant protectants, while males harbored abundant phytopathogens under drought‐stressed conditions. The results could provide potential implications for the selection of suitable poplar sex to plants in drought or semi‐drought habitats. [ABSTRACT FROM AUTHOR]