A new crop science and modelling approach to improve mechanistic understanding and quantification of abiotic and biotic stress interactions and their impacts 

Global warming has already resulted in higher frequencies and severity of multiple abiotic and biotic stresses occurring concurrently or subsequently in farmers’ fields. This trend will likely amplify in the next decades. Yet, to date, the mechanisms determining interactions between abiotic and biotic stresses and their effects on crop performance under field conditions are unknown for most crops and stress combinations. Field data are particularly scarce and, hence, adequate modelling approaches do not exist so far. While crop‐growth models are the most appropriate tools for quantifying climate change effects, they remain largely radiation use efficiency (RUE)‐based, treating stress effects through empirical reductions in photosynthesis or yield (e.g., drought-related multipliers) rather than using explicit carbon reallocations. Critically, they ignore active defense sinks - the substantial fraction of assimilates moved into mucilage, phenolics and other biochemicals that protect plants under stress.This paper aims to describe a novel crop science and modelling approach, in which new empirical knowledge from the genetic to the field scale is integrated and formalized in the novel “MultiStress model” - implemented for maize.There are many examples of crop defence mechanisms towards multiple abiotic and biotic stressors and their interactions that come at carbon costs. Here, we focus on drought-response and illustrate the implementation of the MultiStress model for mucilage exudation under drought conditions. Many water-stressed plants including maize release root mucilage, a gelatinous polysaccharide that maintains rhizosphere moisture. This “hydraulic sponge” keeps soil around drying roots hydraulically conductive, facilitating higher water uptake in dry soil. Yet, the mucilage benefits come at a cost. It has been estimated that about 10–15% of total carbon assimilation may be diverted into mucilage under drought. This represents a large carbon sink that otherwise could have fueled grain production. Current crop models lack any pool for mucilage, so this carbon diversion is simply “lost” from the crop carbon budget. Empirical stress factors downscale growth but do not track where the saved carbon goes to. Most crop models impose a fractional yield loss under drought but cannot differentiate whether the plant invested extra carbon in mucilage or other survival mechanisms. This leads to misallocation of carbon, and overestimated yield and yield stability, since the metabolic cost of mucilage is never subtracted. The MultiStress model explicitly accounts for such carbon costs.Current process-based crop models are neither fit for generating the knowledge needed for assessing crop impacts of climate-induced multiple stress interactions; nor for the task of informing breeding of climate-resilient crop cultivars. Overcoming these challenges requires a renewal of crop science and modelling as shown and currently under development by the MultiStress Research Unit.