Early root–root interactions weaken foliar defense responses against Septoria tritici blotch in a durum wheat varietal mixture

The interactions between co-cultivated plant cultivars are increasingly recognized as influencing their susceptibility to pathogens in mixtures. However, the underlying mechanisms remain largely unexplored. Using a model of durum wheat cultivar mixtures where susceptibility to Septoria foliar disease is increased, we combined aerial and root phenotyping with transcriptional analyses and untargeted metabolomics to elucidate the potential signaling cascade driving this modulation of susceptibility. We observed contrasting root architectures between cultivars in mixtures. Molecular analysis showed a delayed induction of defense-related genes and metabolites following pathogen inoculation in plants grown in mixtures compared with in a pure stand. The findings suggest that root architecture potentially triggers a competitive response that could delay the induction of defense responses following pathogen inoculation. Altogether, these results point to a possible interplay between root architecture, resource competition, plant metabolism, and defense modulation in shaping plant-pathogen interactions within varietal mixtures.