Host response of Nicotiana benthamiana to the parasitism of five populations of root-lesion nematode, Pratylenchus coffeae, from China

In a recent survey of nematodes associated with tobacco in Shandong, China, the root-lesion nematode Pratylenchus coffeae was identified using a combination of morphology and molecular techniques. This nematode species is a serious parasite that damages a variety of plant species. The model plant benthi, Nicotiana benthamiana, is frequently used to study plant-disease interactions. However, it is not known whether this plant species is a host of P. coffeae. The objectives of this study were to evaluate the parasitism and pathogenicity of five populations of the root-lesion nematode P. coffeae on N. benthamiana.N. benthamiana seedlings with the same growth status were chosen and inoculated with 1,000 nematodes per pot. At 60 days after inoculation, the reproductive factors (Rf = final population densities (Pf)/initial population densities (Pi)) for P. coffeae in the rhizosphere of N. benthamiana were all more than 1, suggesting that N. benthamiana was a good host plant for P. coffeae.Nicotiana. benthamiana infected by P. coffeae showed weak growth, decreased tillering, high root reduction, and noticeable brown spots on the roots. Thus, we determined that the model plant N. benthamiana can be used to study plant-P. coffeae interactions.

Pratylenchus smoliki, a new nematode species (Pratylenchidae: Tylenchomorpha) from the Great Plains region of North America

Pratylenchus smoliki is a new species of root-lesion nematode described from corn-soybean production fields in the Central Great Plains of North America. It is characterized by populations with relatively abundant males, two lip annuli, females with a round functional spermatheca and a conoid to subcylindrical tail with a non-crenate, smooth terminus. In host preference tests, corn and wheat produce the largest nematode populations, whereas sorghum and soybeans produce less than 20% the numbers observed on corn. Scanning electron microscopy reveals that the en face patterns compare to those seen in Pratylenchus pseudocoffeae, P. scribneri, P. hexincisus, and P. alleni. The pattern is described as rectangular to trapezoidal subdorsal and subventral lips adjoining oral disc, but with a clear demarcation between the oral disc and the subdorsal and subventral sectors. A Maximum Likelihood COI tree recognizes P. smoliki as a moderately-well-supported clade with several haplotype subgroups. A Maximum Likelihood partial 28S tree provides strong support for the P. smoliki clade and reinforces the close relationships between species with similar en face patterns. Topotype specimens of P. alleni were demonstrably different from P. smoliki using DNA markers. The geographic range of P. smoliki overlaps with the ranges of P. alleni, P. scribneri, P. neglectus, P. hexicisus, and P. dakotaensis. The observed host range (corn, rye, sunflower, and wheat) suggests that P. smoliki may be native to the tallgrass prairie region of the Great Plains.

A QTL on the Ca7 chromosome of chickpea affects resistance to the root-lesion nematode Pratylenchus thornei

The root-lesion nematode Pratylenchus thornei Sher & Allen, 1953 is a damaging parasite of many crop plants, including the grain legume chickpea (Cicer arietinum L.). Within cultivated chickpea, there are no known sources of strong resistance to P. thornei, but some cultivars have partial resistance. In the research reported here, the genetic basis for differences in P. thornei resistance was analysed using a population derived by accelerated single seed descent from a cross between a partially resistant cultivar, PBA HatTrick, and a very susceptible cultivar, Kyabra. A genetic linkage map was constructed from genotyping-by-sequencing data. Two quantitative trait loci were mapped, one on the Ca4 chromosome and one on the Ca7 chromosome. The Ca7 locus had a greater and more consistent effect than the Ca4 locus. Marker assays designed for single nucleotide polymorphisms on Ca7 were applied to a panel of chickpea accessions. Some of these markers should be useful for marker-assisted selection in chickpea breeding. Haplotype analysis confirmed the Iranian landrace ICC14903 to be the source of the resistance allele in PBA HatTrick and indicated that other Australian cultivars inherited the same allele from other Iranian landraces. A candidate region was defined on the Ca7 pseudomolecule. Within that region, 69 genes have been predicted with high confidence. Among these, two have annotations related to biotic stress response. Three others have previously been reported to be expressed in roots of PBA HatTrick and Kyabra, including one that is more highly expressed in PBA HatTrick than in Kyabra.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-021-01271-8.

Intraspecific variation in phenotypic and phylogenetic features among Pratylenchus penetrans isolates from Wisconsin, USA

Pratylenchus penetrans is a common and important agricultural pest in Wisconsin, a USA state with a diverse agriculture. We compared populations from around the state to each other and to data published for populations around the world to gain insight on the variability of features important for identification of this cosmopolitan species. Thirteen isolates from samples collected in soybean fields in ten Wisconsin counties were established in monoxenic cultures. Analysis of morphological features revealed the least variable feature for all isolates collectively was vulva percentage. Features less variable within than among isolates were body width, lip region height, and stylet length. Some isolates showed only the smooth tail tip phenotype and others had a mix of smooth and annulated tail phenotypes. A suite of features provided sufficient pattern to group isolates into four clusters according to hierarchical agglomerative clustering and canonical discriminative analyses, but not with enough distinction to be useful for classification. Haplotype analysis based on the COI mitochondrial gene of the 13 cultured isolates, 39 Wisconsin field populations, and published sequences representing five additional USA states and six countries revealed 21 haplotypes, 15 of which occurred in Wisconsin. Ten haplotypes represented in Wisconsin were shared with populations from Europe, South America, Africa, or Asia. Five haplotypes were unique to Wisconsin, six were unique to The Netherlands, and one was unique to Japan suggesting that even more COI diversity will be revealed when more COI sequences for P. penetrans become available. The maximum pairwise sequence variation was 6% and the SNPs did not alter amino acids, indicating cryptic biodiversity within the species worldwide. The cosmopolitan to localized scale of distribution of COI haplotypes could be due to frequent and ongoing dispersal events, facilitated by life history traits and the broad host range of P. penetrans. Regions of diverse agriculture, like Wisconsin, show promise for studying this important pest and our study confirms the utility of the COI mtDNA gene for studying variation within a species.

New data on known species of Hirschmanniella and Pratylenchus (Rhabditida, Pratylenchidae) from Iran and South Africa

Hirschmanniella anchoryzae from Iran and Pratylenchus hippeastri from South Africa were recovered during a survey of plant-parasitic nematodes belonging to the family Pratylenchidae. Both species were studied using morphological and molecular techniques. Hirschmanniella anchoryzae is identified based on the flattened head, short stylet (19–22 µm), excretory pore position (anterior to pharyngo-intestinal junction), spicule length (27–30 µm), and existence of an axial mucro at the tail end. Phylogenetic analysis using 28S rDNA showed monophyly of Hirschmanniella which Iranian H. anchoryzae placed close to H. halophila (EU620464; EU620465). This result was supported by the principal component analysis of Hirschmanniella species. SEM observation of the South African population of P. hippeastri showed the presence of two annuli in the lip region. Morphometric characters resembled those of specimens earlier reported from South Africa. Hierarchal cluster using morphometrical criteria showed that the Floridian (USA) and South African populations form a group. However, the principal component analysis showed variation within this species. The molecular study of P. hippeastri populations using 18S, ITS, 28S rDNA, and COI of mtDNA showed that all P. hippeastri cluster in one group and confirmed the identification of the species using both morphological and molecular techniques. In addition, the results indicated that South African populations group close to the USA populations. Illustrations of both species including light and scanning electron microscopy observations for P. hippeastri are provided.

Gaud) in response to root-lesion nematode infection

Ramie fiber extracted from stem bark is one of the most important natural fibers. The root-lesion nematode (RLN) Pratylenchus coffeae is a major ramie pest and causes large fiber yield losses in China annually. The response mechanism of ramie to RLN infection is poorly understood. In this study, we identified genes that are potentially involved in the RLN-resistance in ramie using Illumina pair-end sequencing in two RLN-infected plants (Inf1 and Inf2) and two control plants (CO1 and CO2). Approximately 56.3, 51.7, 43.4, and 45.0 million sequencing reads were generated from the libraries of CO1, CO2, Inf1, and Inf2, respectively. De novo assembly for these 196 million reads yielded 50,486 unigenes with an average length of 853.3bp. A total of 24,820 (49.2%) genes were annotated for their function. Comparison of gene expression levels between CO and Inf ramie revealed 777 differentially expressed genes (DEGs). The expression levels of 12 DEGs were further confirmed by real-time quantitative PCR (qRT-PCR). Pathway enrichment analysis showed that three pathways (phenylalanine metabolism, carotenoid biosynthesis, and phenylpropanoid biosynthesis) were strongly influenced by RLN infection. A series of candidate genes and pathways that may contribute to the defense response against RLN in ramie will be helpful for further improving resistance to RLN infection.