Early blight, caused by Alternaria spp., is a major tomato disease that reduces yield and fruit quality. The objective of this study was to evaluate the efficacy of hydroalcoholic propolis extracts (PHEs) from five regions of Santa Catarina, Brazil, against A. linariae in tomato plants. The total phenolic content of the extracts ranged from \(\:13.02\) to \(\:50.62\:\mu\:g\) gallic acid equivalents (GAE) \(\:m{L}^{-1}.\) In greenhouse bioassays, PHEs reduced disease severity by over 90%, with SJ1O being the most effective (94.1% reduction, lowest area under the disease progress curve, AUDPC). Systemic activity was observed, with efficacy near in treated leaves and ~ 50% in untreated ones. PHEs also suppressed spore germination (up to 85%) and fungal colonization (up to 87%). Biochemical analyses showed that PHEs enhanced the activities of ascorbate peroxidase (APX), catalase (CAT), superoxide dismutase (SOD), and lipoxygenase (LOX), and stimulated phenylalanine ammonia lyase (PAL) activity and lignin accumulation, leading to lower reactive oxygen species (ROS) accumulation and lipid peroxidation. Collectively, these results demonstrate the novelty of propolis extracts as resistance elicitors in tomato. Importantly, this study provides the first evidence that hydroalcoholic propolis extracts from Santa Catarina, Brasil, can suppress early blight in tomato by activating both antioxidant defenses and phenylpropanoid metabolism, resulting in strong reduction of pathogen development and host tissue damage, and highlighting propolis as a promising, eco-friendly tool for sustainable early blight management.
