Resistance Phenotyping and WGCNA Identify Oxidative-Defense Hub Regulators in Strawberry Challenged by Colletotrichum siamense

Strawberry anthracnose caused by Colletotrichum siamense threatens global strawberry production. Traditional chemical control faces environmental and safety challenges, making resistant cultivar development critical for sustainability. This study aimed to rank 10 cultivars’ resistance to C. siamense Cs.4J and clarify temporal redox and transcriptomic drivers of resistance. We evaluated resistance using the disease index (DI), observed oxidative stress indicators [peroxidase (POD), hydrogen peroxide (H2O2), malondialdehyde (MDA), catalase (CAT)], and conducted Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis and weighted gene coexpression network analysis (WGCNA). Significant resistance differences emerged: ‘Tianxianzui’ (TXZ) was resistant (DI 10.0–20.0%), while ‘Miaoxiang7’ (MX7) was highly susceptible (DI > 50%). ‘MX7’ showed sustained POD overactivation, progressive H2O2 accumulation, and high MDA (severe oxidative damage); ‘TXZ’ maintained redox balance via earlier CAT activation. KEGG identified 5 key pathways (e.g., phenylpropanoid biosynthesis), and Weighted Gene Co-expression Network Analysis (WGCNA) revealed 2 core modules (resistance-related red, susceptibility-related brown) plus 2 hub genes (FvRNF144B-like [Fragaria vesca RING Finger Protein 144B-like], FaPHR1-like [Fragaria × ananassa PHR1-like]). ‘TXZ’ and ‘MX7’ represent resistant/susceptible cultivars; early CAT activation for redox balance is a key resistance trait. The 5 pathways and 2 hub genes provide a theoretical basis for future functional validation and exploring strawberry–C. siamense interaction mechanisms.