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Polyphasic Characterization of Pigmented Strains of Xanthomonas Pathogenic to Cashew Trees

The export of cashew (Anacardium occidentale) nuts generates millions of dollars for the Brazilian economy annually. However, production may be limited by the occurrence of diseases that affect cashew trees, such as Xanthomonas spot and angular leaf spot, which are caused by pigmented strains of Xanthomonas and Xanthomonas citri pv. anacardii, respectively. Thirty-one pigmented strains of Xanthomonas were characterized for phenotypic, pathogenic, and molecular attributes. These strains were similar to X. citri pv. anacardii in phenotypical characteristics, sensitivity to antibiotics and copper compounds used in agriculture, epidemiology, and repetitive sequence-based polymerase chain reaction (rep-PCR) profiles. When inoculated into Brazilian pepper, cashew, mango, and hog plum seedlings, the pigmented strains of Xanthomonas and X. citri pv. anacardii produced similar symptoms. However, the pigmented strains of Xanthomonas were more aggressive toward cashew plants than toward the other hosts tested, which confirms their specificity. We conclude that pigmented strains of Xanthomonas are very aggressive on cashew trees and should not be considered casual pathogens of these hosts. Moreover, based on our results from rep-PCR and IS1595-PCR amplification, we suggest that these strains constitute a variant of X. citri pv. anacardii.