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

Agricultural systems are increasingly exposed to climatic conditions that vary sharply between and within seasons rather than shifting smoothly around a warming mean. Three consequences of this instability are frequently discussed together yet rarely evaluated as a single causal chain: the intensification of drought and heat, the co-occurrence of these hazards with epidemics of fungal and bacterial crop pathogens, and the resulting divergence between attainable and realised yields. This review examines whether the available evidence supports the proposition that overlapping abiotic and biotic stress is a distinct and growing determinant of the crop yield gap, or whether the proposition rests largely on the juxtaposition of separate literatures. Peer-reviewed studies retrieved from open scholarly indexes, together with reports from recognised intergovernmental bodies, were appraised for design adequacy, measurement validity, ecological relevance and consistency. The synthesis indicates that the strongest evidence concerns the yield penalty of simultaneous water deficit and high temperature, where controlled experiments, statistical yield models and process-based simulations converge on responses that exceed the sum of the individual stresses. Evidence for changing pathogen distributions and for thermal and hydraulic modulation of plant immunity is mechanistically coherent but geographically uneven and dominated by a small number of model pathosystems. The weakest link is the third overlap itself: very few studies observe drought, heat and disease within the same fields and seasons, and yield-gap decompositions seldom attribute losses to biotic causes. Confidence that compound climatic volatility systematically widens yield gaps through disease is therefore lower than the frequency of the claim implies. Priorities include long-term multi-stress field networks, disease-aware yield-gap accounting, and crop models that represent pathogens as dynamic rather than exogenous constraints. Adaptation planning should treat combined stress as a plausible but incompletely quantified risk.