Journal of nematology最新文献

Many root-knot nematode (RKN) species in the genus Meloidogyne occur in Florida, including M. enterolobii, a species able to overcome RKN resistance genes in many crops. The distribution of these nematodes in horticultural crops is not well known. A RKN survey was conducted in South and Central Florida aiming to: (i) identify RKN infecting vegetables, fruit, and other crops; (ii) document host plants; (iii) determine RKN distribution; and (iv) gain insight on the relatedness of M. enterolobii obtained in this study with other populations from the USA and other countries. A total of 304 soil and root samples were collected from 56 plant species cultivated in commercial vegetable and fruit farms, research farms, horticultural gardens, Asian vegetable farms, and natural landscapes in 12 counties. Meloidogyne species identification was performed using mitochondrial haplotype-based identification, species-specific primers, DNA sequencing and phylogenetic analysis. RKN were detected in 247 out of 304 (81.25%) root samples collected from September 2019 to January 2023. Five RKN species (M. arenaria, M. enterolobii, M. hapla, M. incognita and M. javanica) were identified. The most prevalent RKN were M. incognita and M. enterolobii, which were found in 25% of the samples. Less prevalent were M. javanica, found in 16%, and M. arenaria and M. hapla, found in 8% and 5% of samples, respectively. Mixed populations of M. enterolobii and M. incognita were found in 1% of the samples. Phylogenetic analysis showed low genetic variability among DNA sequences of M. enterolobii populations from Florida, other states in the USA, and other countries. New host records found in this study include: a worldwide host record, Solanum capsicoides (M. enterolobii); new US continental host records, Vigna unguiculata (M. enterolobii), Opuntia cochenillifera (mixed species - M. enterolobii and M. incognita). Additionally, new state host records found were Cannabis sativa, Colocasia esculenta, and Lilium sp. (M. arenaria), Phaseolus vulgaris (M. enterolobii), Cucumis melo (M. hapla), and Lavandula angustifolia and Helianthus annuus (M. incognita). These findings confirm the predominance of tropical RKN species, and especially of M. enterolobii, in Florida. and provide new insights into the distribution, prevalence, and hosts of RKN species in horticultural crops in Central and South Florida.

We briefly review the history and development of recognizing nematode assemblages as indicators of environmental conditions. We highlight the effects of spatio-temporal successional changes in nematode assemblages on the auto-regeneration of ecosystem functions after disturbance. We expand on the need for herbivory components in the analysis of soil nematode assemblages in recognition of the important impact of plant parasitism on the resources and productivity of the soil system. Finally, we point out some important areas of research that would enhance the process and value of nematode faunal analysis. We include an evaluation of the current potential for molecular assessment of nematode abundance and function and for the application of artificial intelligence in automated nematode identification.

In this survey, 14 populations of Mesocriconema xenoplax were collected from the rhizosphere of eight fruit and nut trees in Fars province, Southern Iran. The phylogenetic relationships of these populations with other representatives of the species were investigated using sequences of cytochrome c oxidase subunit 1 mitochondrial gene (COI) and D2-D3 expansion fragments of 28S rDNA. Phylogenetic studies indicated a close relationship of the currently sequenced populations with known haplotype groups (HG) in the COI tree and revealed two separate lineages in the 28S rDNA tree. Moreover, the genetic diversity of the populations was analyzed using seven ISSR primers as molecular markers. The estimated genetic diversity among populations regarding associated trees and geographic regions were low values of 3.3% and 5.9%, respectively, indicating high gene flow among the recovered nematode populations. On the other hand, the estimated fixation index (F_ST) was higher for associated plants than for geographic regions (0.611 vs 0.504) indicating that plant-based population segregation better explains genetic diversity in this species. This work expands our knowledge of the genetic structure of this cosmopolitan species of plant-parasitic nematodes.

Molecular data should be combined with morphological data to enhance the reliability of phylogenetic and diagnostic studies on nematodes. In this study, the citrus nematode Tylenchulus semipenetrans collected from citrus orchards in different localities in Fars province, southern Iran, was characterized using the partial sequencing of ITS rDNA, D2-D3 of 28S rDNA and COI mtDNA genes. We also morphometrically characterized the second-stage juveniles (J2) and male specimens. The results showed that T. semipenetrans is a genetically homogeneous species, and only minor nucleotide differences were detected among the populations. Phylogenetic studies demonstrated that most Iranian populations were grouped together, and there were no differences among the populations. However, sequence alignment of ITS, D2-D3 of 28S rDNA and COI mtDNA revealed 17, 24, and 16 single nucleotide variations (SNVs) and 11, 12, and 11 single-nucleotide polymorphisms (SNPs), respectively. The results of the morphometric analysis showed slight morphometric differences among and within the populations of T. semipenetrans. The morphometric differences among citrus nematode populations and the haplotype topology of the populations did not correlate with their geographical origin and host type. The constructed phylogenetic trees showed a close relationship between Tylenchulus and Trophotylenchulus. In addition, the phylogenetic relationships showed that T. musicola is the closest taxon to T. semipenetrans. The results of this study provide a better understanding of the diversity of T. semipenetrans populations and may shed light on the genetic variation of citrus nematode.

During a nematode survey in Iran, an abundant population of sheathoid, migratory, root-ectoparasitic nematodes was recovered from a tea, Camellia sinensis (L.), Kuntze plantation for the first time. Morphological and molecular characterization identified the Iranian population as Hemicriconemoides kanayaensis. The morphometrics of H. kanayaensis agreed with the original description. Phylogenetic relationships within Hemicriconemoides-based on ITS region, D2 to D3 expansion regions of the 28S rRNA, and the partial 18S rRNA genes along with the partial mitochondrial COI gene-confirmed the occurrence of H. kanayaensis on the tea plantation in Iran. Principal component analysis (PCA) confirmed the high intraspecific and interspecific variabilities among Hemicriconemoides species and between H. kanayaensis populations.

Root-knot nematodes were discovered in severely declining creeping bentgrass putting greens at a golf course in Indian Wells, Riverside County, California. The exhibited disease symptoms included chlorosis, stunted growth, and dieback. Based on morphological examination and measurements of J2 females and males, it was suggested that the causal pathogen was Meloidogyne marylandi. This identification was confirmed by analysis of the D2-D3 expansion segments of 28S rRNA and COI gene sequences. The host status of 28 plant species was evaluated in greenhouse trials. All tested monocots, except rye and Allium species, were found to be hosts, while no reproduction occurred on dicots. Temperature-tank experiments helped determine that the life cycle of M. marylandi was completed between 17-35 °C, with a base temperature of 8.3 °C and a required heat sum of 493 degree-days (DD). In greenhouse trials in pasteurized soil and near-ideal growing conditions, M. marylandi did not cause significant growth reduction of creeping bentgrass cv. Penn A-4, even at very high J2 inoculation densities. It is highly probable that other biotic and abiotic factors contributed to the observed putting green damage.

The ring nematode, Mesocriconema xenoplax, has become recognized as a widespread pest of sweet cherry trees in the Okanagan Valley of British Columbia (BC). Understanding the cumulative impacts of M. xenoplax on tree health, interpreting diagnostic sample data, and predicting the impacts of climate change on M. xenoplax population densities all depend on knowledge of the temporal dynamics of M. xenoplax populations and their linkage with soil temperature and moisture regimes. The objective of this study was to measure population densities of M. xenoplax on a monthly basis over five years, in relation to soil temperature and moisture regimes, in a 16-year-old irrigated sweet cherry orchard. We tested the following hypotheses: (i) population densities would start low each spring and increase continuously with soil degree-day heat accumulation during each growing season, and (ii) year-to-year variation in population growth during the growing season would be correlated with year-to-year variation in soil degree-day heat accumulation. The data did not support these hypotheses and indicated that although there were significant differences in population densities among sample dates, there were no regular seasonal cycles of population growth and decline. We suggest that in mature cherry orchards, density-dependent processes mask the influences of annual changes in soil temperature and moisture on population processes. The data indicate that for diagnostic sampling purposes, all seasons would be equally representative of M. xenoplax population densities in irrigated orchards in BC. Furthermore, the lack of any strong linkage between soil temperature regimes and within- or across-year population dynamics indicate that modeling efforts based solely on abiotic drivers of temperature and moisture would not likely represent changes in population dynamics of M. xenoplax that will actually occur with climate change.

Crop rotation has been a commercial practice for managing the sugarbeet cyst nematode (Heterodera schachtii, SBCN) since the 1950s. Research conducted in southern California established that SBCN populations decline at the rate of 49% to 80% per year, leading to estimates that three- to four-year rotations to nonhost crops would be sufficient to reduce SBCN densities to nondamaging levels. Following grower reports that much longer rotations were needed in central California, trials were conducted to establish the rate of decline of SBCN in the San Joaquin Valley. Ten commercial fields with a history of SBCN infestation were sampled periodically for up to 6.3 years. In each field, 10 circular subplots located 30.5 meters apart (each with a 6-m radius) were established with reference to a permanent landmark. On each sampling date, 12 subsamples from each subplot were taken randomly from the top 0 cm to 30 cm of soil and composited into a single sample. Standard techniques were utilized to extract and count cysts and eggs from soil samples. Average yearly rates of population decline in the sampled fields ranged from 11.4% to 25.8%. This finding has implications for SBCN management in California sugarbeets grown for biofuel, as the lower decline rates indicate that longer nonhost rotation periods than previously anticipated may be necessary.

Panagrolaimus namibiensis n. sp. was recovered and cultured from soils collected under Arthraerua leubnitziae (pencil-bush) in the Namib Desert of Namibia, one of the driest terrestrial habitats on Earth. It is described here based on morphometrics, scanning electron micrographs, light images, line drawings, and molecular data. The new species is distinguished by having a conspicuous posterior deirid, a hook-shaped stegostomal dorsal tooth, and anterior deirids and excretory pore aligned at mid-bulb. It was morphologically compared to eleven well-described species in the genus with which it shared similar labial structure (six distinct rounded lips, and low lip segments separated in pairs), conoid tail, and/or a lateral field with three incisures, including P. labiatus, P. kolymaensis, P. davidi, P. rigidus, and P. superbus. Bayesian phylogenetic analyses using SSU and LSU rDNA each placed P. namibiensis n. sp. within clades of Panagrolaimus species, although the two trees resolved its relationship to previously described species differently. Furthermore, our analyses showed the genus is not monophyletic. In a laboratory experiment, P. namibiensis n. sp. survived exposure to 0% relative humidity for 24 h, demonstrating the anhydrobiotic ability of this species that contributes to its survival in the Namib Desert.

Root-knot nematodes (RKNs) are the most destructive nematode species in main pistachio cultivation areas of Iran, and adversely affect crop quality and yield. So far, Meloidogyne incognita and M. javanica have been reported infecting pistachio. In this study, four populations of M. arenaria were found infecting pistachio in Kerman and Khorasan Razavi provinces. The morphology and morphometrics of the recovered populations closely match the data given for other populations of the species. Molecular characterization of the recovered populations was performed by sequencing three genomic and mitochondrial regions, including D2-D3 of LSU rDNA, COII-16S and Nad5 mtDNA. The D2-D3 sequences had more than 99% identity with many sequences of tropical species. The COII-16S sequences had more than 99% identity with sequences of M. arenaria, M. morocciensis and M. thailandica. The Nad5 sequences had 99.81% identity with some sequences of M. arenaria. The D2-D3 and COII-16S sequences of M. arenaria did not form independent clades in corresponding Bayesian trees, but Nad5 sequences formed a monophyletic group in corresponding phylogeny. Based on this study, M. arenaria is present in Iran's pistachio gardens, necessitating appropriate management measures.