Abstract
Bacterial leaf scorch, associated with the bacterial pathogen Xylella fastidiosa, is a widely established and problematic disease of landscape ornamentals in Washington D.C. A multi-locus sequence typing analysis was performed using 10 housekeeping loci for X. fastidiosa strains in order to better understand the epidemiology of leaf scorch disease in this municipal environment. Samples were collected from 7 different tree species located throughout the District of Columbia, consisting of 101 samples of symptomatic and asymptomatic foliage from 84 different trees. Five strains of the bacteria were identified. Consistent with prior data, these strains were host specific, with only one strain associated with members of the red oak family, one strain associated with American elm, one strain associated with American sycamore, and two strains associated with mulberry. Strains found for asymptomatic foliage were the same as strains from the symptomatic foliage on individual trees. Cross transmission of the strains was not observed at sites with multiple species of infected trees within an approx. 25 m radius of one another. X. fastidiosa strain specificity observed for each genus of tree suggests a highly specialized host-pathogen relationship.
Highlights
Xylella fastidiosa [1] is a bacterial pathogen and causal agent of numerous diseases of agricultural crops throughout the Americas
The STs10 in our analysis corresponded to previously established STs for X. fastidiosa published at pubmlst.org (Table 2)
Each tree genus was generally associated with a single unique X. fastidiosa ST10; ST10-1 (ST-9 in pubmlst.org), associated with members of the red oak family; red oak, pin oak, scarlet oak, and willow oak; ST10- 2 (ST-8) associated with American sycamore, ST10-3 (ST-41) associated with American elm, and ST10-4 and ST10-5 associated with mulberry (Table 3)
Summary
Xylella fastidiosa [1] is a bacterial pathogen and causal agent of numerous diseases of agricultural crops throughout the Americas. Several of the most significant diseases caused by X. fastidiosa include the Pierce’s disease of grapevine [2], citrus variegated chlorosis [3], almond leaf scald [4], and phony peach disease [5]. In addition to leaf-scorching diseases inflicted on many woody perennial cash crops, urban forests of several eastern-Atlantic municipalities share a similar fate [6,7,8,9,10,11]. X. fastidiosa causes a chronic leaf-scorching disease often referred to as bacterial leaf scorch (BLS) [12].
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