Integrative Structural, Physiological, and Transcriptomic Analyses Reveal Key Determinants of Anthracnose Resistance in Rubber Tree (Hevea brasiliensis)

Anthracnose, caused by Colletotrichum spp., is a major foliar disease limiting rubber tree (Hevea brasiliensis) productivity. To uncover resistance mechanisms, we compared resistant and susceptible germplasm using an integrated framework combining leaf structural analysis, physiological defense profiling, and transcriptome sequencing. Resistant germplasm exhibited lower stomatal density and more compact mesophyll, likely restricting pathogen entry and within-leaf spread. Following inoculation, resistant accessions showed stronger antioxidant responses, with higher activities of superoxide dismutase (SOD) and peroxidase (POD), and elevated phenylpropanoid-related enzymes, including polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL), peaking at 24–48 h post inoculation. These responses were accompanied by enhanced reactive oxygen species (ROS) accumulation (H₂O₂) but reduced lipid peroxidation (malondialdehyde), indicating efficient oxidative stress regulation. Microscopic observation revealed delayed infection progression and postponed differentiation of infection structures in resistant germplasm. Transcriptomic analysis further demonstrated that differentially expressed genes were mainly enriched in pathways related to signal transduction and secondary metabolism, particularly phenylpropanoid metabolism and related secondary metabolic pathways. Together, these results suggest that anthracnose resistance is mediated by coordinated structural barriers, redox homeostasis, and transcriptional regulation of defense networks. This study provides a mechanistic framework for resistance-oriented breeding and the utilization of resistant germplasm in rubber tree.