Priming and memory in ancient olive cultivars: Enhancing drought resilience through rhizosphere microbial consortia under repeated stress cycles

Understanding how olive cultivars respond to recurrent drought is critical to develop climate-resilient cropping systems. This study investigated the physiological, biochemical, and molecular responses of three autochthonous cultivars (Ortice, Ortolana, Racioppella) exposed to repeated water deficit, with and without inoculation of a PGPR consortium ( Bacillus subtilis , Pseudomonas fluorescens ). Under stress, Ortolana maintained stable water status, Ortice exhibited progressive adaptive plasticity, while Racioppella showed heightened stress sensitivity with limited recovery capacity. Microbial inoculation enhanced the accumulation of osmolytes (proline, soluble sugars) and antioxidants (phenols, flavonoids), and mitigated pigment degradation. At the molecular level, drought induced strong upregulation of NCED1 and repression of PP2C , while inoculated plants displayed a tempered transcriptional response, suggesting effective priming. Upon the second stress exposure, LEA46 and DHN1 expression increased markedly, particularly in Ortice, indicating activation of stress memory. Expression of OePIP2.1 aquaporin declined under drought, consistent with reduced membrane water permeability; however, cultivar-specific patterns emerged, implying differential regulatory strategies. The microbial consortium appeared to reinforce both primed and memory-based responses. These findings demonstrate that integrating tolerant genotypes with functional microbial inoculants enhances drought resilience through coordinated physiological regulation and timely modulation of stress-responsive genes, supporting sustainable olive production in water-limited environments. • Microbial inoculation enhanced drought resilience in olive under repeated stress cycles. • Racioppella showed strong but inefficient response; Ortolana had conservative stability. • PGPR treatment increased osmoprotectants and antioxidants in stressed olive leaves. • Gene expression revealed ABA-dependent priming and stress memory in tolerant cultivars. • Aquaporin regulation and pigment dynamics were cultivar-specific and stress-modulated.