Facilitation between intercropped species increases micronutrient acquisition, subsequently controlling rust disease on maize

Global food security is threatened by plant disease, and crop diversification often promotes productivity through reduced disease and facilitation for increased nutrient acquisition. However, whether such facilitation is a factor in disease resistance is unknown. We conducted five intercropping field experiments with various crop combinations at two sites for four years, and conducted a meta-analysis of literature to investigate how crop diversity affects crop productivity and rust disease on maize. Legume-based intercropping increased the aboveground biomass of intercropped maize by 8.1% and grain yields by 10.2% in comparison to non-legume-based intercropping. Disease severity on maize intercropped with legumes was reduced by 45.3% and 47.7%, compared to monocultures of maize and maize intercropped with non-legumes, respectively. Moreover, as interactions among intercrops became more facilitative, the concentrations of zinc (Zn), copper (Cu) and iron (Fe) in maize increased, and these increases were highly correlated with decreasing disease severity. The global meta-analysis was consistent with our field experiments, as lower disease severity was associated with greater intensity of interspecific facilitation or with lower intensity of interspecific competition. In sum, lower disease severity was closely related to enhanced acquisition of disease-resistant nutrients driven by stronger interspecific facilitative effects in intercropping systems. Facilitative effects on maize was increased by the identity of leguminous companion crop species, and was increased by sufficient irrigation, but reduced by applications of nitrogen and phosphorus fertilizers. Our findings identify a novel facilitative mechanism in general and advance the understanding of the facilitative mechanisms that underly disease control through crop diversification.