Xylella fastidiosa, 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 X. fastidiosa, we conducted DNA-DNA relatedness assays and sequenced the 16S-23S intergenic spacer (ITS) region using 26 strains from 10 hosts. Under stringent conditions (Tm -15 degrees C), the DNA relatedness for most X. fastidiosa strains was *70%. However, at high stringency (Tm -8 degrees C), three distinct genotypes (A, B, and C) were revealed. Taxon A included strains from cultivated grape, alfalfa, almond (two), and maple, interrelated by 85% (mean); taxon B included strains from peach, elm, plum, pigeon grape, sycamore, and almond (one), interrelated by 84%; 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 58, 41, and 45%, respectively. ITS results also indicated the same grouping; 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 Pierce's disease agar medium whereas B and C strains grow more slowly. Taxon B and C 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. fastidiosa [correction] subsp. nov, subsp. multiplex, subsp. nov., and subsp. pauca, subsp. nov., respectively. The type strains of the subspecies are subsp. fastidiosa [correction] ICPB 50025 (= ATTC 35879T and ICMP 15197), subsp. multiplex ICPB 50039 (= ATTC 35871 and ICMP 15199), and subsp. pauca ICPB 50031 (= ICMP 15198).

中文翻译：

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Xidiella fastidiosa亚种：X. fastidiosa亚种。[更正] fastidiosa [更正]子空间。十一月，X。fastidiosa子亚种。多重亚种 十一月和X. fastidiosa子亚种。包卡亚种 十一月

尽管有遗传学研究支持多种分类，但木虱小病杆菌是导致100多种植物致病的一种细菌，被归类为单一物种。为了确定X.fastidiosa菌株之间的分类学相关性，我们进行了DNA-DNA相关性分析，并使用来自10个宿主的26个菌株对16S-23S基因间隔区（ITS）区域进行了测序。在严格条件下（Tm -15摄氏度），大多数X. fastidiosa菌株的DNA相关性为* 70％。然而，在高严格度（Tm -8摄氏度）下，发现了三种不同的基因型（A，B和C）。分类群A包括来自栽培葡萄，苜蓿，杏仁（两个）和枫树的菌株，相互之间的关联度为85％（平均值）；B类群包括桃，榆，李，鸽葡萄，无花果和杏仁（一种）的菌株，相互关联的占84％；而分类单元C仅包括来自柑橘的菌株，相互关联87％。分类单元A和B，A和C，B和C之间的平均倒数相关性分别为58、41和45％。ITS结果也表明相同的分组。A和B，A和C以及B和C的类群分别具有98.7％，97.9％和99.2％的身份。以前和现在的表型数据支持分子数据。分类群A菌株在皮尔斯氏病琼脂培养基上生长较快，而B和C菌株则生长较慢。分类群B和C菌株对青霉素敏感，对羧苄青霉素具有抗性，而A菌株则相反。每个分类单元可以通过血清学以及结构蛋白来区分。我们建议将分类单元A，B和C命名为X. fastidiosa subsp。fastidiosa [更正]子空间。十一月 多重，亚种 十一月。包卡亚族 分别。亚种的类型菌株是亚种。fastidiosa [更正] ICPB 50025（= ATTC 35879T和ICMP 15197），子版本。复用ICPB 50039（= ATTC 35871和ICMP 15199），以及 pauca ICPB 50031（= ICMP 15198）。