Bacterial wilt caused by the soil-borne pathogen Ralstonia solancearum is economically devastating, with no effective methods to fight the disease. This pathogen invades plants through their roots and colonizes their xylem, clogging the vasculature and causing rapid wilting. Key to preventing colonization are the early defense responses triggered in the host's root upon infection, which remain mostly unknown. Here, we have taken advantage of a high-throughput in vitro infection system to screen natural variability associated with the root growth inhibition phenotype caused by R. solanacearum in Arabidopsis during the first hours of infection. To analyze the genetic determinants of this trait, we have performed a genome-wide association study, identifying allelic variation at several loci related to cytokinin metabolism, including genes responsible for biosynthesis and degradation of cytokinin. Further, our data clearly demonstrate that cytokinin signaling is induced early during the infection process and cytokinin contributes to immunity against R. solanacearum. This study highlights a new role for cytokinin in root immunity, paving the way for future research that will help in understanding the mechanisms underpinning root defenses.

Cell and Molecular Biology Colorado State University Fort Collins CO 80523 USA

Centre for Research in Agricultural Genomics Bellaterra Barcelona Spain

Department of Bioagricultural Sciences and Pest Management Colorado State University Fort Collins CO 80523 USA

Genetics Department University of Barcelona Barcelona Spain

Gregor Mendel Institute Dr Bohr Gasse 3 Vienna 1030 Austria

Laboratory of Growth Regulators Olomouc The Czech Republic

Salk Institute For Biological Studies Plant Molecular and Cellular Biology Laboratory 10010 N Torrey Pines Rd La Jolla CA 92037 USA

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