A Simplified and Integrated View of Disease Control in Varietal Mixtures Using the Phytobiome Framework

Increasing intraspecific diversity within crop systems is a promising strategy to manage aerial diseases, particularly those caused by fungal aerial pathogens. This review examines how cultivar mixtures reduce disease incidence and severity using the phytobiome framework, identifying three major types of processes: (1) physical ones, which alter disease dynamics through dilution effects, barrier effects, and microclimate modifications; (2) processes that are mediated by microbial interactions, which influence disease severity via induced resistance and indirect plant-plant interactions mediated by the microbiome; and (3) processes involving direct plant-plant interactions, where danger signaling and signaling from healthy neighbors modulate plant physiology and immunity through resource management and molecular cues. This review provides a comprehensive understanding of how cultivar mixtures enhance disease resistance and emphasizes that direct plant-plant interactions are likely stronger contributors than so far considered. It highlights the need for further research into the roles of microbiomes and direct plant-plant interactions to optimize mixtures' performance.