Induction of Systemic Resistance in Pepper (Capsicum annuum) against Phytophthora Blight and Plant Growth Using Biotic and Abiotic Inducers

Pepper ( Capsicum annuum ) is a globally important horticultural crop valued in both fresh markets and processing industries. Production is severely constrained by Phytophthora capsici, a destructive oomycete responsible for root and crown rot, foliar infections, and significant yield losses, underscoring the need for effective, sustainable management strategies. This study assessed an integrated treatment regimen comprising humic acid (HA; 30% liquid), Phosphozist, Effective Microorganisms (EM) (photosynthetic bacteria, lactobacillus, streptomyces, actinomycetes, yeast, etc.), Tricuran P ( Trichoderma harzianum T 22), Bordeaux Fix (fungicide), and Formycine Gold PX 20% (6, 8, and 10 L ha −1 ), applied for their preventive and curative potential against P. capsici . Inoculated pepper seedlings were treated, and responses were measured across four domains: biomass production, disease severity index, macro- and microelement content, and antioxidant defenses including peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), polyphenol oxidase (PPO), and chitinase activities. Data revealed dose-dependent effects, with Formycine Gold at 10 L ha −1 yielding the greatest improvements in growth, nutrition, and enzyme activity. Biomass increased 1.56- to 3.59-fold, while nutrient uptake rose by 15.59–156.65%, compared with infected controls. Antioxidant activity increased 1.19- to 4.39-fold for the EM and Formycine Gold at 10 L ha −1, respectively, in comparison to the inoculated controls, reflecting enhanced reactive oxygen species (ROS) scavenging and defense priming. Disease suppression was substantial: Formycine Gold (10 L ha −1 ) achieved up to 93% reduction, Phosphozist achieved up to 48%, and EM showed comparatively modest efficacy (7%). Findings support synergistic interactions among biochemical and microbial amendments, promoting both plant vigor and pathogen suppression. Efficacy was genotype- and environment-dependent, highlighting the need for field validation, cost–benefit analysis, and mechanistic studies on priming and resistance induction under diverse production conditions.