Contrasting Response of Santina and Bing Sweet Cherry Cultivars Under Combined Biotic and Abiotic Stress

Climate change is intensifying the simultaneous occurrence of biotic and abiotic stresses in fruit crops, but yet the molecular mechanisms underlying plant responses remain poorly understood. The physiological and transcriptomic responses of two sweet cherry (<i>Prunus avium</i> L.) cultivars, Santina and Bing, grafted onto Gisela 12, were investigated under single and combined stresses imposed by <i>Pseudomonas syringae</i> pv. <i>syringae</i> and water deficit. Although biomass, gas exchange, and hormone accumulation showed only minor changes, combined stress triggered distinct cultivar-dependent transcriptional reprogramming. The cultivar Bing exhibited a pronounced response with 4261 differentially expressed genes (DEGs), characterized by strong repression of photosynthetic processes and activation of defense- and hormone-related pathways. In contrast, the cultivar Santina showed a moderate response with 674 DEGs, primarily reinforcing structural and secondary metabolism. Cultivar-specific modulation of abscisic acid sensitivity was associated with the contrasting regulation of WRKY40 and Sin3-like repressors, despite comparable ABA levels. Strikingly, both cultivars upregulated the <i>GIGANTEA</i> gene, underscoring its role as a central regulatory hub linking circadian rhythm, stomatal function, and hormonal crosstalk under dual stress. Collectively, these results reveal non-additive, genotype-specific transcriptional strategies in sweet cherry trees, providing insights into stress integration in fruit trees and identifying regulatory genes that may inform breeding and management strategies for resilience under climate change.