Activation of Phenylpropanoid and Oxidative Defense Enzymes (PAL, POX, PPO) in Field Pea (Pisum Sativum L.) by Trichoderma-Based Biocontrol Treatments Against Powdery Mildew (Erysiphe Pisi DC.)

Biocontrol agents (BCAs) not only antagonize pathogens but also prime host defensive metabolism. This study quantified the induction of three defense enzymes—phenylalanine ammonia-lyase (PAL), peroxidase (POX) and polyphenol oxidase (PPO)—in field pea (Pisum sativum cv. Arkel) following seed treatments with Trichoderma afroharzianum (T₃), Trichoderma asperellum (T₆) and a bioconsortia (SHEP-6 + T. asperellum Th-31, T5), under challenge by Erysiphe pisi DC. Leaves sampled 15 days post-inoculation were assayed for enzyme activities. All BCA treatments significantly (ANOVA, p = 0.05) increased PAL, POX and PPO activities relative to the inoculated untreated control. PAL peaked at 3.12 n mol cinnamic acid min^-1 g^-1 fresh tissue in T₃/T₅ (≈2.6× control), POX reached 0.058 ΔA₄₂₀ min^-1 mg^-1 protein in T₅/T₃ (≈2.3× control), and PPO attained 0.042 ΔA₄₂₀ min^-1 mg^-1 protein in T₅ (≈2.3× control). The strong co-induction of PAL with oxidative enzymes suggests coordinated activation of the phenylpropanoid pathway and oxidative cross-linking reactions that reinforce cell walls and produce antimicrobial phenolic quinones. The bioconsortia (SHEP-6 + T. asperellum) elicited the highest responses, indicating potential synergism. These biochemical changes likely contribute to the reduced powdery mildew development observed in other parts of the study. Results support integrating Trichoderma-based bioformulations into pea disease management to induce durable resistance via metabolic priming.