Affiliation:
1. Department of Biology
2. Department of Entomology, University of California, Riverside, California 92521
Abstract
ABSTRACT
Xylella fastidiosa
is a pathogen that causes leaf scorch and related diseases in over 100 plant species, including Pierce's disease in grapevines (PD), phony peach disease (PP), plum leaf scald (PLS), and leaf scorch in almond (ALS), oak (OAK), and oleander (OLS). We used a high-resolution DNA sequence approach to investigate the evolutionary relationships, geographic variation, and divergence times among the
X. fastidiosa
isolates causing these diseases in North America. Using a large data set of 10 coding loci and 26 isolates, the phylogeny of
X. fastidiosa
defined three major clades. Two of these clades correspond to the recently identified
X. fastidiosa
subspecies
piercei
(PD and some ALS isolates) and
X. fastidiosa
subsp.
multiplex
(OAK, PP, PLS, and some ALS isolates). The third clade grouped all of the OLS isolates into a genetically distinct group, named
X. fastidiosa
subsp.
sandyi
. These well-differentiated clades indicate that, historically,
X. fastidiosa
has been a clonal organism. Based on their synonymous-site divergence (∼3%), these three clades probably originated more than 15,000 years ago, long before the introduction of the nonnative plants that characterize most infections. The sister clades of
X. fastidiosa
subsp.
sandyi
and
X. fastidiosa
subsp.
piercei
have synonymous-site evolutionary rates 2.9 times faster than
X. fastidiosa
subsp.
multiplex
, possibly due to generation time differences. Within
X. fastidiosa
subsp.
multiplex
, a low level (∼0.1%) of genetic differentiation indicates the recent divergence of ALS isolates from the PP, PLS, and OAK isolates due to host plant adaptation and/or allopatry. The low level of variation within the
X. fastidiosa
subsp.
piercei
and
X. fastidiosa
subsp.
sandyi
clades, despite their antiquity, suggests strong selection, possibly driven by host plant adaptation.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
112 articles.
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