Molecular Induction of Defense-Related Genes in Major Fruit Trees by Native Pseudomonas protegens Strains

Chile is a global leader in the fruit industry; however, the sector faces significant yield losses due to phytopathogens and an urgent need to reduce reliance on chemical fungicides. Induction of plant defenses and priming offer sustainable alternatives by activating the plant’s innate immune system. This study aimed to evaluate the ability of native Pseudomonas protegens strains and their formulations to trigger plant defenses responses in five agronomically important fruit crops: kiwifruit (Actinidia chinensis var. deliciosa), walnut (Juglans regia), cherry (Prunus avium), blueberry (Vaccinium corymbosum), and grapevine (Vitis vinifera). Under controlled conditions, a randomized block design was implemented with four treatments, including P. protegens strains and their formulations, as well as a chemical elicitor (acibenzolar-S-methyl) as a positive control. Foliar treatments were applied, and leaf tissues were sampled at 1 day, 7 days, and 14 days post-inoculation. Transcriptional responses were quantified via qPCR using the ΔΔC_t method, targeting key defense-related genes, including pathogenesis-related proteins (pr1, pr2, pr3, pr4, pr5, pr10), and enzymes of the phenylpropanoid and signaling pathways (pal, chs, ppo, lox9, glc). This study provides a molecular framework for understanding how biological inducers modulate stress memory in perennial crops. The results obtained highlight the potential of native bacteria to be integrated into sustainable integrated pest management programs, offering an alternative strategy to enhance fruit crop resilience through the activation of natural plant defense responses.