Seemüller Erich, Schneider Bernd
Biologische Bundesanstalt für Land- und Forstwirtschaft, Institut für Pflanzenschutz im Obstbau, D-69221 Dossenheim, Germany.
Int J Syst Evol Microbiol. 2004 Jul;54(Pt 4):1217-1226. doi: 10.1099/ijs.0.02823-0.
Apple proliferation (AP), pear decline (PD) and European stone fruit yellows (ESFY) are among the most economically important plant diseases that are caused by phytoplasmas. Phylogenetic analyses revealed that the 16S rDNA sequences of strains of each of these pathogens were identical or nearly identical. Differences between the three phytoplasmas ranged from 1.0 to 1.5% of nucleotide positions and were thus below the recommended threshold of 2.5% for assigning species rank to phytoplasmas under the provisional status 'Candidatus'. However, supporting data for distinguishing the AP, PD and ESFY agents at the species level were obtained by examining other molecular markers, including the 16S-23S rDNA spacer region, protein-encoding genes and randomly cloned DNA fragments. The three phytoplasmas also differed in serological comparisons and showed clear differences in vector transmission and host-range specificity. From these results, it can be concluded that the AP, PD and ESFY phytoplasmas are coherent but discrete taxa that can be distinguished at the putative species level, for which the names 'Candidatus Phytoplasma mali', 'Candidatus Phytoplasma pyri' and 'Candidatus Phytoplasma prunorum', respectively, are proposed. Strains AP15R, PD1R and ESFY-G1R were selected as reference strains. Examination of available data on the peach yellow leaf roll (PYLR) phytoplasma, which clusters with the AP, PD and ESFY agents, confirmed previous results showing that it is related most closely to the PD pathogen. The two phytoplasmas share 99.6% 16S rDNA sequence similarity. Significant differences were only observed in the sequence of a gene that encodes an immunodominant membrane protein. Until more information on this phytoplasma is available, it is proposed that the PYLR phytoplasma should be regarded as a subtype of 'Candidatus Phytoplasma pyri'.
苹果增殖病（AP）、梨衰退病（PD）和欧洲核果黄化病（ESFY）是由植原体引起的最具经济重要性的植物病害。系统发育分析表明，这些病原体各菌株的16S rDNA序列相同或几乎相同。这三种植原体之间的差异在核苷酸位置的1.0%至1.5%之间，因此低于在“暂定种”状态下为植原体指定种级别的推荐阈值2.5%。然而，通过检查其他分子标记，包括16S - 23S rDNA间隔区、蛋白质编码基因和随机克隆的DNA片段，获得了在种水平上区分AP、PD和ESFY病原体的支持数据。这三种植原体在血清学比较中也存在差异，并且在介体传播和寄主范围特异性方面表现出明显差异。从这些结果可以得出结论，AP、PD和ESFY植原体是连贯但离散的分类单元，可在假定的种水平上区分，为此分别提出了“苹果植原体暂定种（Candidatus Phytoplasma mali）”、“梨植原体暂定种（Candidatus Phytoplasma pyri）”和“李植原体暂定种（Candidatus Phytoplasma prunorum）”的名称。选择菌株AP15R、PD1R和ESFY - G1R作为参考菌株。对与AP、PD和ESFY病原体聚类的桃黄叶卷叶病（PYLR）植原体的现有数据进行检查，证实了先前的结果，表明它与PD病原体关系最为密切。这两种植原体的16S rDNA序列相似度为99.6%。仅在编码免疫显性膜蛋白的基因序列中观察到显著差异。在获得关于这种植原体的更多信息之前，建议将PYLR植原体视为“梨植原体暂定种（Candidatus Phytoplasma pyri）”的一个亚型。
