Effects of abiotic and biotic elicitors on tomato resistance to tomato brown rugose fruit virus

Tomato brown rugose fruit virus (ToBRFV) has become a major threat to global tomato production, causing significant economic losses. Due to the limited efficacy of conventional control methods, alternative strategies are urgently needed. This study evaluated the effects of biotic and abiotic elicitors-including bacterial polysaccharides from Pseudomonas fluorescens 1442 and Burkholderia gladioli G15, salicylic acid (SA), and mechanical wounding-on resistance induction in tomato plants infected with ToBRFV. The experiment was conducted in a greenhouse under controlled environmental conditions, using a completely randomized design with seven treatments and five replicates. Bacterial elicitors were applied via foliar spray in two applications at one-week intervals; a 0.5 mM SA solution was similarly applied, and mechanical wounding was induced using a sterile punch. Disease severity was visually assessed at pre-flowering, flowering, and fruiting stages. Defense responses were evaluated by measuring the activities of catalase (CAT), peroxidase (POD), and phenylalanine ammonia-lyase (PAL), as well as the expression of defense-related genes, Pathogenesis-Related Protein 1b (PR1b), Coronatine-Insensitive Protein 1 (COI1), and Nonexpressor of PR Genes 1 (NPR1), using qRT-PCR. The results indicated that the combined P. fluorescens and B. gladioli (P + B) treatment significantly enhanced defense enzyme activities, upregulated gene expression, and reduced symptom severity more effectively than individual treatments. Additionally, the combined elicitor treatment improved plant growth parameters, suggesting a synergistic effect that offers a promising strategy for ToBRFV management.