Department of Plant Pathology, Faculty of Agriculture, Tarbiat Modares University, Tehran, Iran.
Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, United States of America.
PLoS One. 2019 Jun 26;14(6):e0217506. doi: 10.1371/journal.pone.0217506. eCollection 2019.
Three populations of Xiphinema primum n. sp. and two populations of X. pachtaicum were recovered from natural forests and cultural regions of northern Iran. Both species belong to the X. americanum-group and were characterized by their morphological, morphometric and molecular data. The new species, which was recovered in three locations, belongs to the X. brevicolle-complex and is characterized by 2124-2981 μm long females with a widely rounded lip region separated from the rest of the body by a depression, 103-125 μm long odontostyle, two equally developed genital branches with endosymbiont bacteria inside the ovary, which are visible under light microscope (LM), vulva located at 51.8-58.0%, the tail is 26-37 μm long with a bluntly rounded end and four juvenile developmental stages. It was morphologically compared with nine similar species viz. X. brevicolle, X. diffusum, X. incognitum, X. himalayense, X. luci, X. parabrevicolle, X. paramonovi, X. parataylori and X. taylori. The second species, X. pachtaicum, was recovered in two geographically distant points close to city of Amol. Molecular phylogenetic studies of the new species were performed using partial sequences of the D2-D3 expansion segments of the large subunit ribosomal RNA gene (LSU rDNA D2-D3), the internal-transcribed spacer rDNA (ITS = ITS1+5.8S+ITS2), and the mitochondrial cytochrome c oxidase I gene (COI mtDNA) regions. The Iranian population of X. pachtaicum was also phylogenetically studied based upon its LSU rDNA D2-D3 sequences. Both species were also inspected for their putative endosymbiont bacteria. Candidatus Xiphinematobacter sp. was detected from two examined populations of the new species, whereas the second endosymbiont bacterium, detected from three examined isolates of X. pachtaicum, was related to the plant and fungal endosymbionts of the family Burkholderiaceae. The phylogenetic analyses of the two endosymbiont bacteria were performed using partial sequences of 16S rDNA. In cophylogenetic analyses, significant levels of cophylogenetic signal were observed using both LSU rDNA D2-D3 and COI mtDNA markers of the host nematodes and 16S rDNA marker of the endosymbiont bacteria.
三种新的 Xiphinema primum n. sp. 和两种 X. pachtaicum 种群从伊朗北部的自然森林和文化区中被回收。这两个物种都属于 X. americanum 组，并通过形态学、形态计量学和分子数据进行了特征描述。在三个地点回收的新物种属于 X. brevicolle 复合体，其特征是雌虫长 2124-2981μm，具有宽阔圆形的唇区，与身体的其余部分通过凹陷分开，有 103-125μm 长的齿状突，两个同样发达的生殖枝，在卵巢内有共生细菌，在光镜（LM）下可见，阴门位于 51.8-58.0%处，尾部长 26-37μm，末端钝圆，有四个幼体发育阶段。它与九种类似的物种进行了形态比较，即 X. brevicolle、X. diffusum、X. incognitum、X. himalayense、X. luci、X. parabrevicolle、X. paramonovi、X. parataylori 和 X. taylori。第二种 X. pachtaicum 是在距离阿摩尔市不远的两个地理位置遥远的地方回收的。对新物种的分子系统发育研究是使用核糖体 RNA 基因（LSU rDNA D2-D3）大亚基的 D2-D3 扩展片段、内部转录间隔区 rDNA（ITS=ITS1+5.8S+ITS2）和线粒体细胞色素 c 氧化酶 I 基因（COI mtDNA）区域的部分序列进行的。还基于其 LSU rDNA D2-D3 序列对伊朗的 X. pachtaicum 种群进行了系统发育研究。还检查了这两个物种的潜在共生细菌。从新物种的两个检查种群中检测到候选 Xiphinematobacter sp.，而从三个检查的 X. pachtaicum 分离株中检测到的第二种共生细菌与伯克霍尔德氏菌科的植物和真菌共生体有关。使用 16S rDNA 的部分序列对两种共生细菌进行了系统发育分析。在共进化分析中，使用宿主线虫的 LSU rDNA D2-D3 和 COI mtDNA 标记以及共生细菌的 16S rDNA 标记观察到共生细菌的共进化信号具有显著水平。
