Xylella fastidiosa: an examination of a re‐emerging plant pathogen

• Published in: Molecular plant pathology 2018-04, Vol.19 (4), p.786-800
• Main Authors: Rapicavoli, Jeannette, Ingel, Brian, Blanco‐Ulate, Barbara, Cantu, Dario, Roper, Caroline
• Format: Article
• Language: English
• Subjects: Abscission; Berries; Chlorosis; citrus; Citrus variegated chlorosis; Defoliation; Desiccation; Dieback; Drying; Endophytes; Food plants; Fruit trees; Fruits; Gammaproteobacteria; Gangrene; Gram-negative bacteria; grapevine; Host range; Host specificity; Leaf scorch; Leaves; Necrosis; Nutrient deficiency; olive; Ornamental plants; Pathogen Profile; Pathogens; Pierce's disease; Plant diseases; Plant species; Senescence; Taxonomy; Tree crops; tyloses; Wilting; Xanthomonadaceae; Xylella fastidiosa; xylem
• ISSN: 1464-6722; 1364-3703
• DOI: 10.1111/mpp.12585

Summary Xylella fastidiosa is a Gram‐negative bacterial plant pathogen with an extremely wide host range. This species has recently been resolved into subspecies that correlate with host specificity. This review focuses on the status of X. fastidiosa pathogenic associations in plant hosts in which the bacterium is either endemic or has been recently introduced. Plant diseases associated with X. fastidiosa have been documented for over a century, and much about what is known in the context of host–pathogen interactions is based on these hosts, such as grape and citrus, in which this pathogen has been well described. Recent attention has focused on newly emerging X. fastidiosa diseases, such as in olives. Taxonomy Bacteria; Gammaproteobacteria; family Xanthomonadaceae; genus Xylella; species fastidiosa. Microbiological properties Gram‐negative rod (0.25–0.35 × 0.9–3.5 μm), non‐flagellate, motile via Type IV pili‐mediated twitching, fastidious. Host range Xylella fastidiosa has a broad host range that includes ornamental, ecological and agricultural plants belonging to over 300 different species in 63 different families. To date, X. fastidiosa has been found to be pathogenic in over 100 plant species. In addition, it can establish non‐symptomatic associations with many plants as a commensal endophyte. Here, we list the four distinct subspecies of X. fastidiosa and some of the agriculturally relevant diseases caused by them: X. fastidiosa ssp. fastidiosa causes Pierce's disease (PD) of grapevine (Vitis vinifera); X. fastidiosa ssp. multiplex causes almond leaf scorch (ALS) and diseases on other nut and shade tree crops; X. fastidiosa ssp. pauca causes citrus variegated chlorosis (CVC) (Citrus spp.), coffee leaf scorch and olive quick decline syndrome (OQDS) (Olea europaea); X. fastidiosa ssp. sandyi causes oleander leaf scorch (OLS) (Nerium oleander). Significant host specificity seemingly exists for some of the subspecies, although this could be a result of technical biases based on the limited number of plants tested, whereas some subspecies are not as stringent in their host range and can infect several plant hosts. Disease symptoms Most X. fastidiosa‐related diseases appear as marginal leaf necrosis and scorching of the leaves. In the case of PD, X. fastidiosa can also cause desiccation of berries (termed ‘raisining’), irregular periderm development and abnormal abscission of petioles. In olive trees affected with OQDS, leaves exhibit marginal necrosis and