<i>Xanthomonas oryzae</i> pathovars: model pathogens of a model crop

<jats:title>SUMMARY</jats:title> <jats:p> <jats:italic>Xanthomonas oryzae</jats:italic> pv. oryzae and <jats:italic>Xanthomonas oryzae</jats:italic> pv. oryzicola cause bacterial blight and bacterial leaf streak of rice ( <jats:italic>Oryza sativa</jats:italic> ), which constrain production of this staple crop in much of Asia and parts of Africa. Tremendous progress has been made in characterizing the diseases and breeding for resistance. <jats:italic>X. oryzae</jats:italic> pv. oryzae causes bacterial blight by invading the vascular tissue, while <jats:italic>X. oryzae</jats:italic> pv. oryzicola causes bacterial leaf streak by colonizing the parenchyma. In rice there are 29 major genes for resistance to bacterial blight, but so far only a few quantitative resistance loci for bacterial leaf streak. Over 30 races of <jats:italic>X. oryzae</jats:italic> pv. oryzae have been reported. Both pathogens exhibit genetic variation among isolates. Mechanisms of pathogenesis and resistance have begun to be elucidated. Members of the AvrBs3/PthA family of transcription activator‐like effectors play a major role in the virulence of <jats:italic>X. oryzae</jats:italic> pv. oryzae and possibly <jats:italic>X. oryzae</jats:italic> pv. oryzicola. Cloning of six rice resistance genes for bacterial blight and one from maize effective against bacterial leaf streak has uncovered a diversity of structure and function, some shared by genes involved in defence in animals. This article reviews research that spans a century. It also presents a perspective on challenges for sustainable control, and opportunities that interactions of <jats:italic>X. oryzae</jats:italic> pathovars with rice present as models for understanding fundamental aspects of bacterial pathogenesis of plants and plant disease resistance, as well as other aspects of plant and microbial biology, with implications also for animal innate immunity. </jats:p>