Plant Stress Biology in a Warming World: Synergies in Abiotic and Biotic Adaptation

Crop production is increasingly exposed to climate extremes and pathogen pressure at the same time rather than in isolation, yet the evidence base that informs crop protection has been assembled largely from single-factor experiments. This critical narrative review examines how heat, water deficit, excess soil water, elevated carbon dioxide and their combinations reshape plant immunity, pathogen performance and disease outcome in field crops, and evaluates how securely current conclusions rest on the underlying evidence. Literature was identified through structured searching of open scholarly databases and indexes, supplemented by citation tracking and institutional sources, with the final search conducted on 30 June 2026. Four findings emerge with reasonable confidence. Elevated temperature suppresses several conserved nodes of salicylic acid-dependent immunity, and this suppression has been demonstrated mechanistically in model and crop species. Water deficit acts as neither a consistent aggravator nor a consistent suppressor of disease, and its direction of effect depends on pathogen lifestyle, tissue, timing and genotype. Responses to three or more concurrent stressors are frequently not predictable from responses to the component stressors, and the accumulated burden of individually mild stressors can be substantially damaging. Warming does not act uniformly on disease, because pathogens possess thermal optima and adaptive capacity of their own, and several well-documented systems show reduced infection at elevated temperature. Confidence in these conclusions is constrained by a narrow taxonomic and geographical evidence base, by heavy reliance on controlled-environment studies using stress intensities and application rates that rarely resemble field dynamics, by inconsistent reporting of stress severity, and by the near-absence of multi-season field experiments that impose realistic compound exposure. Progress requires field-scale factorial platforms, standardised reporting of stress dose and timing, systematic testing of resistance durability across thermal and hydrological gradients, and forecasting frameworks that treat host, pathogen and environment as jointly variable.