Xanthomonas arboricola Diseases of Stone Fruit, Almond, and Walnut Trees: Progress Toward Understanding and Management.

Stone fruit (Prunus spp.: apricot, cherry, peach, nectarine, plum, and sloe), almond (Prunus spp.), and walnut (Juglans spp.) crops are among the most economically important tree crops worldwide and are cultivated to a different extent on all continents. The number of countries growing these crops has increased in the last decade with a subsequent increase in acreage globally. Throughout the range of cultivation, Prunus spp. and Juglans spp. are often subjected to pathogen attack. Among them, Xanthomonas arboricola has become markedly important over the last decade. The putative pathovars of X. arboricola, pv. pruni and pv. juglandis, cause bacterial canker and spot and bacterial blight on stone fruits and almond, and on walnut, respectively. In recent years, disease outbreaks caused by X. arboricola on Prunus and on Juglans have increased, as has international concern. The rate at which these outbreaks are occurring suggests the possibility of future epidemics. To address the consequences of such disease emergences, it is important to understand the epidemiology of these diseases, about which little is known to date. The objectives of this review are to provide an overview of X. arboricola diseases of stone fruit, almond, and walnut trees, and to discuss current and future management strategies.