Integrating plant growth regulators and biostimulants to enhance resilient and sustainable raspberry and blackberry production

Raspberry (Rubus idaeus L.) and blackberry (Rubus subgenus Rubus Watson) are high-value small fruit crops facing escalating climate variability and tightening sustainability standards. This review synthesizes recent advances (2009–2025) on plant growth regulators (PGRs) and biostimulants as complementary tools to enhance propagation, canopy architecture, yield, fruit quality, and stress resilience in these crops. PGRs, including auxins, gibberellins, cytokinins, and growth inhibitors, provide targeted, rapid modulation of developmental processes such as rooting, budbreak, shoot elongation, and fruit maturation. Biostimulants, encompassing humic substances, seaweed extracts, microbial inoculants, and protein hydrolysates, confer cumulative benefits by enhancing nutrient uptake, antioxidant capacity, and stress tolerance. While previous reviews have treated PGRs and biostimulants independently, this article evaluates their potential integration, by proposing a stage-specific decision-support framework that combines season-long biostimulant applications with targeted PGR “pulses” at key phenological stages to optimize yield, fruit quality, and resilience, while minimizing chemical inputs. Finally, we identify research priorities including factorial dose-reduction trials, genotype-by-environment interaction studies, and multi-omics analyses to refine cultivar-specific recommendations.