Single vs multiple agroecosystem services provided by common wheat cultivar mixtures: Weed suppression, grain yield and quality

Cultivar mixtures are a well studied practice to improve common wheat performance by exploiting the potential of genetic diversity to buffer biotic and abiotic stresses. However, their ability to reduce weed interference is still unclear. In this work, crop-weed interactions were studied across two growing seasons under Mediterranean climatic conditions on nineteen common wheat stand types: twelve cultivars including modern and heritage varieties, four three-cultivar mixtures, two six-cultivar mixtures and one high diversity mixture with all twelve cultivars. Wheat morphological parameters, biomass accumulation of wheat and weeds, wheat yield, yield components and grain quality were assessed. Heritage cultivars showed the highest weed suppression (on average -67% weed biomass at harvest compared to modern cultivars) due probably to increased height, above ground biomass and leaf area index. No consistent mixture effects were detected for either weed suppression, grain yield or grain quality, when considered separately from one another. However, when considering the three agroecosystem services altogether based on a rank analysis, mixtures with higher number of components (six and twelve) tended to improve the overall crop performance compared to the average of less diverse wheat stand types. Although the observed benefits of mixtures vs component cultivars for individual agroecosystem services (i.e. weed suppression, yield and grain quality) were limited, cultivar mixtures appear as a potential tool to improve overall crop performance, especially with medium to high number of component cultivars. However, increased adoption of cultivar mixtures would require prior identification of key cultivar traits clearly associated with the provision of target agroecosystem services. Enhanced complementarity and synergy among these traits would maximize exploitation of the available genetic agrobiodiversity.