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Cordeirópolis, Brazil

Coletta-Filho H.D.,IAC Centro APTA Citros Sylvio Moreira | Francisco C.S.,IAC Centro APTA Citros Sylvio Moreira | Francisco C.S.,Sao Paulo State University | Almeida R.P.P.,University of California at Berkeley
Phytopathology | Year: 2014

The ecology of plant pathogens of perennial crops is affected by the long-lived nature of their immobile hosts. In addition, changes to the genetic structure of pathogen populations may affect disease epidemiology and management practices; examples include local adaptation of more fit genotypes or introduction of novel genotypes from geographically distant areas via human movement of infected plant material or insect vectors. We studied the genetic structure of Xylella fastidiosa populations causing disease in sweet orange plants in Brazil at multiple scales using fast-evolving molecular markers (simple-sequence DNA repeats). Results show that populations of X. fastidiosa were regionally isolated, and that isolation was maintained for populations analyzed a decade apart from each other. However, despite such geographic isolation, local populations present in year 2000 were largely replaced by novel genotypes in 2009 but not as a result of migration. At a smaller spatial scale (individual trees), results suggest that isolates within plants originated from a shared common ancestor. In summary, new insights on the ecology of this economically important plant pathogen were obtained by sampling populations at different spatial scales and two different time points. © 2014 The American Phytopathological Society.

Coletta-Filho H.D.,IAC Centro APTA Citros Sylvio Moreira | Coletta-Filho H.D.,University of California at Berkeley | Bittleston L.S.,University of California at Berkeley | Almeida R.P.P.,University of California at Berkeley
Applied and Environmental Microbiology | Year: 2011

Vector-borne generalist pathogens colonize several reservoir species and are usually dependent on polyphagous arthropods for dispersal; however, their spatial genetic structure is generally poorly understood. Using fast-evolving genetic markers (20 simple sequence repeat loci, resulting in a total of 119 alleles), we studied the genetic structure of the vector-borne plant-pathogenic bacterium Xylella fastidiosa in Napa Valley, CA, where it causes Pierce's disease when it is transmitted to grapevines from reservoir plants in adjacent riparian vegetation. Eighty-three different X. fastidiosa multilocus microsatellite genotypes were found in 93 isolates obtained from five vineyards, resulting in an index of clonal fraction closer to 0 and a Simpson's genotypic diversity index (D) closer to a maximum value of 1. Moderate values of Nei's gene diversity (HNei; average HNei = 0.41) were observed for most of the X. fastidiosa populations. The low Wright's index of genetic diversity among populations calculated by the FSTAT software (Wright's FST index) among population pairs (0.0096 to 0.1080) indicated a weak or absent genetic structure among the five populations; a panmictic population was inferred by Bayesian analyses (with the STRUCTURE and BAPS programs). Furthermore, a Mantel test showed no significant genetic isolation by distance when both Nei (r = -0.3459, P = 0.268) and linearized Θ (r = -0.3106, P = 0.269) indices were used. These results suggest that the riparian vegetation from which vectors acquire the pathogen prior to inoculation of grapevines supports a diverse population of X. fastidiosa. © 2011, American Society for Microbiology.

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