D Cereal susceptibility to pathogens is impacted by plant-plant interactions

Planting a crop variety with another has long been considered as a way to control epidemics at the field level, and is experiencing a revival of interest in agriculture. Indeed, the more diverse the fields, the higher the probability to limit pathogen dispersal (Reiss & Drinkwater, 2018; Mundt 2002). Yet, the ability of mixture to control pests has been shown highly variable and often unpredictable in the field (Mundt 2002; Smithson & Lenne 1996). This suggests that beyond dispersal barrier generated by genotypic diversity, several understudied processes are involved. Scarce evidence suggests the existence of other mechanisms of modulation of plant susceptibility through genetic diversity in the presence or absence of epidemics (Montazeaud et al., 2022)(Pélissier et al., 2021a). Among them is the recently discovered Neighbour-Modulation of Susceptibility (NMS), which depicts the phenomenon that susceptibility in a given plant is affected by the presence of another healthy neighbouring plant (Pélissier et al., 2021b). Despite the putative tremendous importance of NMS for crop science, its frequency and quantitative contribution to modulating susceptibility in cultivated species remains unknown. Here, using more than 200 pairs of intra-specific genotype mixtures, inoculated with worldwide major pathogen, in both rice and wheat and experimental conditions that precluded any epidemics, we experimentally demonstrate significant modulation of disease susceptibility in a large number of mixtures grown in greenhouse conditions. Thus, the susceptibility of these two major crops results from indirect effects originating from neighbouring plants. Quite remarkably, the levels of susceptibility modulated by plant-plant interactions can reach those conferred by intrinsic basal immunity. These findings open new avenues to develop more sustainable agricultural practices by engineering less susceptible crop mixtures thanks to emergent but predictable properties of mixtures, by selecting appropriate pairs of genotypes among the almost infinite number of possible pairs.

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