Study on the Relationship Between Exogenous Salicylic Acid-Induced Pear Resistance to Black Spot Disease and Lignin Synthesis

Pear black spot disease is a serious fungal disease during pear production; salicylic acid is a core signaling molecule that regulates the expression of plant disease resistance genes. To elucidate the intrinsic association between salicylic acid-induced resistance to pear black spot disease and lignin biosynthesis, in vitro plantlets of two pear cultivars, ‘Xinli No.7’ and ‘Xueqing’, were employed as experimental materials. After 60 h SA pretreatment, the leaves were inoculated with the pathogen Alternaria alternata. Leaf samples were harvested at 0, 8, 16, 24, and 48 h post-inoculation to determine phenylalanine ammonia-lyase activity, quantify lignin content, and analyze the transcript levels of genes involved in lignin synthesis. The results demonstrated that, relative to the untreated control group, SA treatment significantly enhanced phenylalanine ammonia-lyase activity and promoted lignin accumulation in both ‘Xinli No.7’ and ‘Xueqing’. Moreover, multiple key genes associated with lignin biosynthesis—including PbrPAL1, Pbr4CL1, PbrCOMT, PbrCCoAOMT, PbrCAD, and PbrPOD—were markedly upregulated, with their expression levels increasing by 3.5–15 fold. Transcript profiles of PbrHCT1, PbrHCT4, and PbrC3H1 exhibited cultivar-specific divergence between the two varieties. Notably, the susceptible cultivar ‘Xueqing’ displayed a distinct lag phase and attenuated response in the expression of all lignin-related genes compared with the other cultivar. This study provides reference for green prevention and sustainable development of pear.