Diversity and copper resistance of Xanthomonas affecting citrus

Abstract

Since citrus canker was first described in the early 1900's, four major types and three species of pathogenic xanthomonads associated to citrus were identified based on the characteristic symptoms and host range. Type A, caused by X. citri subsp. citri, develops typical raised cankered lesions and is pathogenic on most commercial citrus species and cultivars. Types B and C are caused by X. citri pv. aurantifolii which elicits canker lesions. Besides the typical type A, the more aggressive and most widely spread type, other subtypes have been described, such as type A*, type A w , type A-Manatee, type A-Miami, type A-minus pthA, and type-A etrog. The type B strains are found only in Argentina and are more pathogenic on lemon and less aggressive on sweet orange, tangerines and grapefruit. The type C strains are found only in Brazil and are pathogenic only on Key lime. X. alfalfae subsp. citrumelonis, formerly known as type E, causes citrus bacterial spot and is more aggressive on trifoliate citrus and its hybrids. Lesions caused by citrus bacterial spot are flat or sunken and not raised. Several subtypes of X. citri subsp. citri have also been identified. Besides the differences in pathogenicity, xanthomonads may also vary in their sensitivity to copper. Copper resistance has been reported for strains of X. citri subsp. citri and X. alfalfae subsp. citrumelonis and is conferred by the gene clusters copLAB or copABCD. Resistance to copper has serious implications for the use of copper-based bactericides, which are the most important chemicals for the control of diseases caused by Xanthomonas on citrus. Keywords Citrus bacterial spot. Citrus canker. Xanthomonas alfalfae subsp. citrumelonis. X. citri pv. aurantifolii. X. citri subsp. citri. copABCD. copLAB

Prevalence of Xanthomonas euvesicatoria (formally X. perforans) associated with bacterial spot severity in Capsicum annuum crops in South Central Chihuahua, Mexico

“…Within Xanthomonas strains, detection of copLAB genes indicated copper resistance (Behlau, Gochez & Jones, 2020). Previous studies showed that in culture medium, copLAB genes regulate copper accumulation through copper-binding proteins generation.…”

Overexpression of CsSAMT in Citrus sinensis Induces Defense Response and Increases Resistance to Xanthomonas citri subsp. citri

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Hexanoic acid: a new potential substitute for copper‐based agrochemicals against citrus canker

“…The continuous application of copper generates selective pressure, stimulating the emergence of resistant bacterial strains (Areas et al 2018), which may make this agrochemical inefficient in the near future. For instance, resistance to copper has already emerged in X. citri (Canteros 1999;Behlau et al 2011;Behlau et al 2020).…”