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Title: DESCRIPTION OF NEW SUBSPECIES OF XYLELLA FASTIDIOSA SUBSP. PIERCEI, SUBSP. NOV., X. FASTIDIOSA SUBSP. AGGLOMERII SUBSP. NOV., AND X FASTIDIOSA SUBSP. IDIAOTRAPOSA SUBSP. NOV.

Author
item Schaad, Norman
item POSTNIKOVA, ELENA - UNIV. NEBRASKA
item FATMI, M'BAREK - VET. HASSAN II, MORROCCO
item LACY, GEORGE - VPI, BLACKSBURG, VA
item CHANG, CHUNG-JAN - UNIV. GEORGIA

Submitted to: Systematic and Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2003
Publication Date: 2/20/2004
Citation: Schaad, N.W., Postnikova, E., Fatmi, M., Lacy, G., Chang, C. 2004. Description of new subspecies of xylella fastidiosa subsp. piercei, subsp. nov., x. fastidiosa subsp. agglomerii subsp. nov., and x fastidiosa subsp. idiaotraposa subsp. nov.. Systematic and Applied Microbiology.27:290-300.

Interpretive Summary: Pierce's disease of grape and several other diseases caused by Xylella fastidiosa have become serious diseases. The bacterium is classified as a single species but studies support multiple groupings. To clarify this, we used DNA-based assays and growth in culture to compare 26 strains from 10 hosts, including the highly regulated citrus variegated chlorosis strain. The assays revealed three groups, with more than 70% likeness among strains of each group. Group A contained strains from grape, alfalfa, maple, and almond strains and group B contained strains from peach, elm, plum, wild grape, almond, and sycamore. Group C contained citrus strains, only. We propose groups A, B, and, C be named X. fastidiosa subspecies piercei, agglomeri, and idiotraposa, respectively. This new nomenclature will allow regulatory agencies to clearly differentiate between the highly regulated citrus strain and the other non-regulated strains.

Technical Abstract: Xylella fastidiosa (Xf), a fastidious bacterium causing disease in over 100 plant species, is classified as a single species, although genetic studies support multiple taxons. To determine the taxonomic relatedness among strains of Xf, we conducted DNA-DNA relatedness assays and sequenced the 16S-23S intergenic spacer (ITS) region using 26 strains from 10 hosts. Under normal stringency (Tm-15C), the DNA relatedness for most Xf strains was = 70%. However, at high stringency (Tm-8C), three distinct genotypes (A, B, and C) were revealed. Taxon A included strains from cultivated grape, alfalfa, almond, and maple, interrelated by 86%; taxon B included strains from peach, elm, plum, pigeon grape, sycamore, and almond, interrelated by 82%; and taxon C included only strains from citrus, interrelated by 87%. The mean reciprocal relatedness between taxons A and B, A and C, and B and C, were 56, 39, and 45%, respectively. ITS results generally agreed with the DNA relatedness data; taxons A and B, A and C, and B and C had identities of 98.7, 97.9, and 99.2 %, respectively. Previous and present phenotypic data supports the molecular data. Taxon A strains grow faster on PD2 agar whereas B and C strains grow more slowly. Taxon B strains are susceptible to penicillin and resistant to carbenicillin whereas A strains are opposite. Each taxon can be differentiated serologically as well as by structural proteins. We propose taxons A, B, and C be named X. fastidiosa subsp. piercei, subsp. nov, subsp. agglomeri, subsp. nov., and subsp. idiotraposa, subsp. nov., respectively.