The rice root-knot nematode, Meloidogyne graminicola , is a serious pest in most rice-growing countries. Usually, nematodes employ antioxidants to counteract the harm of reactive oxygen species (ROS) and facilitate their infection. Here the gene encoding M . graminicola protein disulphide isomerase ( MgPDI ) was identified. The deduced protein is highly conserved in the putative active-site Cys-Gly-His-Cys. In situ hybridization showed that MgPDI was specifically localized within esophageal glands of pre-parasitic second stage juveniles (J2s). MgPDI was significantly up-regulated in the late parasitic J2s. Characterization of the recombinant protein showed that the purified MgPDI exhibited similar activities to other oxidases/isomerases such as the refolding of the scrambled RNase and insulin disulfide reductase and the protection of plasmid DNA and living cells from ROS damage. In addition, silencing of MgPDI by RNA interference in the pre-parasitic J2s lowered their multiplication factor. MgPDI expression was up-regulated in the presence of exogenous H 2 O 2 , whereas MgPDI silencing resulted in an increase in mortality under H 2 O 2 stress. MgPDI is localized in the apoplast when transient expression in Nicotiana benthamiana leaves. The results indicated that MgPDI plays important roles in the reproduction and pathogenicity of M . graminicola and it also contributes to protecting nematodes from exogenous H 2 O 2 stress.

Populations of Criconemoides parvus, Discocriconemella hengsungica, and Discocriconemella limitanea, isolated in Hangzhou, China from the rhizosphere soil of woody perennials were characterized morphologically and molecularly. The morphometric data of the Chinese populations were compared with populations from other regions of the world. DNA barcoding with the mitochondrial COI gene confirmed conspecificity of Chinese and Costa Rican populations of D. limitanea. Phylogenetic assessment using a near full-length 18S ribosomal DNA sequence provided weak support for a grouping of Criconemoides parvus from China and C. annulatus from western North America. The phylogenetic position of D. hengsungica from China and an unknown species of Discocriconemella from Thailand relative to D. limitanea suggests that the genus Discocriconemella is not monophyletic. The study provides the first record of D. hengsungica in China and confirms the presence of C. parvus previously reported from China. Biogeographic implications of these nematode distributions are discussed.

Ring nematodes of the genus Criconemoides are a group of polyphagous, migratory rootectoparasites of plants. In a nematological survey of Zhejiang Province, three new Criconemoides species were isolated from the rhizosphere of Citrus sp., Euonymus alatus and Pterocarya stenoptera trees. In the present study, the new species characterized using an integrative taxonomic approach and described as Criconemoides parainformis n. sp., C. geraerti n. sp. and C. rotundicaudatus n. sp. Three of the species shares truncated anteriorly flattened lip region comprised of two annuli, body annuli margin smooth with few anastomoses, (except C. rotundicaudatus n. sp. it has crenated annuli margins and numerous anastomoses), excretory pore 1-2 annuli posterior to pharyngeal bulb base, (except C. geraerti n. sp. it has excretory pore at the same level, or 1-2 annuli anterior to pharyngeal bulb base), vulva closed, anus hardly visible 1-3 annuli posterior to vulva. The new species can be distinguished based on their en face view pattern under scanning electron microscope (SEM) and the tail shapes. i.e. C. parainformis n. sp. has an ellipsoid oral disc, slightly fused pseudolips and tail ending in a bilobed terminus. C. geraerti n.sp. has a hexagonal oral disc, separated pseudolips, and a bluntly conoid tail. C. rotundicaudatus n. sp. has a rounded oral disc, well developed pseudolips, and a short broadly rounded tail. Besides detailed morphological studies using SEM, genomic and mitochondrial molecular data were obtained for the three described new species. In inferred phylogenies, these three species clustered with known Criconemoides species in 18S, 28S, ITS and coxI trees. Currently, only four known Criconemoides species occur in China and the discovery of the three new Criconemoides species in present study has increased our knowledge on the diversity of Criconemoides in China.

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