Integrated Phenotypic, Physiological, Biochemical, and Transcriptomic Analyses Reveal the Molecular Response Mechanisms of Populus to Poplar Canker

The growth process of poplar faces severe environmental challenges. Notably, poplar canker, caused by <i>Botryosphaeria dothidea</i>, has significantly impaired poplar productivity and ecological functions. However, research on the molecular mechanisms underlying poplar resistance to this disease remains incomplete. This study systematically elucidated the molecular mechanisms of <i>Populus davidiana</i> × <i>P. alba</i> var. <i>pyramidalis</i> (Pdpap) in response to <i>B. dothidea</i> stress by integrating phenotypic, physiological, biochemical, and transcriptomic analyses. The results demonstrated that 5 d post-inoculation with <i>B. dothidea</i>, the stem wound sites darkened and developed lesions. Following pathogen infection, H₂O₂ content and SOD and POD activity initially increased then decreased, while MDA content overall showed a declining trend with prolonged infection time. KEGG enrichment analysis revealed that DEGs were significantly enriched in the MAPK signaling pathway, plant hormone signal transduction, and phenylpropanoid biosynthesis pathways. Gene modules significantly associated with physiological indices were screened using WGCNA. Within these modules, hub genes in the regulatory network were further identified, leading to the selection of <i>P2C76</i>. The genome-wide identification of <i>PtrPP2Cs</i> classified 124 members into 13 subgroups. Collectively, this study dissects the gene expression regulation and molecular defense mechanisms of poplar under <i>B. dothidea</i> infection, providing novel molecular insights for its molecular breeding.