Combining wheat with multi-species prairie strips reduces the development of Septoria tritici blotch

Crop diversification, notably through intercropping, is known for regulating disease development in agroecosystems. However, intercropping usually involves two or three species, limiting its potential to enhance ecosystem multifunctionality. This study investigates the impact of “agroprairies”, a cropping system design consisting of alternating narrow strips of wheat and multispecies prairies (∼12 species), on the development of Zymoseptoria tritici , the causal agent of Septoria tritici blotch (STB), a major foliar disease in wheat. Two complementary field experiments were conducted. The first one monitored the incidence and severity of STB under natural epidemic conditions across combinations of four wheat cultivars and four prairie mixtures with contrasted functional traits. The second experiment used above-canopy inoculation on a subset of treatments to assess disease dynamics under high disease pressure, independent of physical barrier effects. Rhizosphere microbiomes were analyzed before inoculation to evaluate enrichment in taxa associated with plant defense and disease suppression. Under natural conditions, STB incidence and severity were reduced by 52% and 41% in two agroprairie types compared to monocrop. Prairie biomass and specific leaf area (SLA) were identified as key factors associated with this reduction. When the disease was inoculated above the canopy, this reduction effect disappeared, highlighting the dominant role of physical barriers in disease regulation. However, one agroprairie treatment still reduced disease progression by 18%, suggesting the involvement of additional regulatory mechanisms. Microbiome analysis revealed shifts in bacterial beta diversity and an enrichment of potentially beneficial taxa in the wheat rhizosphere, although no direct link with disease regulation was established.