Ring Nematode Research Articles

Flood irrigation applications of sodium tetrathiocarbonate reduce severity of ring nematode and bacterial canker in prunes

Flood irrigation applications of sodium tetrathiocarbonate reduce severity of ring nematode and bacterial canker in prunes

Molecular characterisation and diagnostics of the red ring nematode, Bursaphelenchus cocophilus, from Mexico

Summary The red ring nematode, Bursaphelenchus cocophilus, vectored by the South American palm weevil, Rhynchophorus palmarum, is the causal agent of red ring disease in coconut and other palms in countries of Central and South America. The populations of B. cocophilus collected in the states of Guerrero and Tabasco, Mexico, were molecularly characterised using the D2-D3 expansion segments of 28S rRNA, ITS rRNA and COI gene sequences. Mexican B. cocophilus populations were molecularly different from other Central and South American populations. Comparative analysis of available rRNA sequences obtained from several countries showed that B. cocophilus consists of molecularly different populations and its species structure is likely congruent with that of the beetle vector. Conventional PCR, real-time PCR and recombinase polymerase amplification (RPA) with lateral flow dipstick (LF) assays have been developed for the identification of the red ring nematode in this study. The specificity of the ITS rRNA primers in the assays were examined using B. cocophilus and other 15 species of family Aphelenchoididae. Detection sensitivity levels, determined by using a dilution series of B. cocophilus extracts, was 0.13 nematode per reaction tube for real-time PCR and 0.25 nematode per reaction tube for conventional PCR and LF-RPA assays. The application of the LF-RPA assay has great potential for diagnosing infestation of this species with a minimal laboratory infrastructure.

The more we search, the more we find: discovering and expanding the biodiversity in the ring nematode genus Xenocriconemella De Grisse and Loof, 1965 (Nematoda: Criconematidae)

The ring nematode genus Xenocriconemella De Grisse and Loof, 1965 comprises only one nominal species, Xenocriconemella macrodora (Taylor, 1936) De Grisse and Loof, 1965. The initial objective of the present study was to investigate the morphological–morphometric and molecular diversity of 28 X. macrodora populations in the Iberian Peninsula associated with tree forests (mainly Quercus spp.). However, a detailed integrative taxonomic analysis (morphological–morphometric and molecular data) from each population and analysis of this data using principal component analysis (PCA) for morphometric data (including these 28 populations and other 25 X. macrodora populations around the world) and molecular and phylogenetic species delimitation methods revealed that X. macrodora forms a species complex. This species complex is composed by species that are morphometricly and morphologically similar, but clearly different at the molecular level. Three new species are described applying integrative taxonomy, namely as Xenocriconemella iberica sp. nov., Xenocriconemella paraiberica sp. nov. and Xenocriconemella pradense sp. nov. However, the molecular diversity of this species in USA and Italy confirmed that additional species are likely present in this species complex, and the diversity of this group may be higher than expected. The study of X. macrodora topotypes can clarify the position of this species using molecular markers under an integrative approach.

The Impact of Peach Rootstocks and Winter Cover Crops on Reproduction of Ring Nematode

Two peach rootstocks (‘Guardian’ and ‘MP-29’) and ten winter cover crops (rye, wheat, barley, triticale, oat, Austrian winter pea, crimson clover, balansa clover, hairy vetch, and daikon radish) were evaluated in a greenhouse environment to determine their suitability to host ring nematode, Mesocriconema xenoplax. Each crop was inoculated with 500 ring nematodes, and the experiments were terminated 60 days after inoculation. The reproduction factor (ratio of final and initial nematode population) ranged from 0 to 13.8, indicating the crops greatly varied in their host suitability to ring nematode. ‘Guardian’ has been known to tolerate ring nematode; however, results from the current study suggest the tolerance statement is anecdotal. Another peach rootstock, ‘MP-29’, was also a good host for ring nematode, suggesting an urgency to develop ring nematode-resistant peach rootstocks. Wheat supported the least to no nematode reproduction while pea supported the greatest reproduction. The rest of the cover crops were poor to good hosts to ring nematodes. Although planting cover crops in peach orchards is not common, employing non or poor host crops can help suppress nematodes in addition to having soil health benefits. Furthermore, peach breeding programs should focus on finding and introgressing ring nematode resistance in commercial rootstocks.

Depth distribution of plant-parasitic nematodes on bentgrass golf greens in Missouri and Indiana.

Control of plant-parasitic nematodes (PPNs) on golf putting greens with nematicides is dependent on the seasonal occurrence and depth distribution of target PPN populations. This study aimed to determine if plant-parasitic nematode populations on golf course putting greens in Missouri and Indiana peaked at a targetable depth at a specific time in the year, focusing primarily on lance (Hoplolaimus spp.) and root-knot (Meloidogyne spp.) nematodes. To elucidate species diversity in the region, rDNA from a subset of lance and root-knot nematodes was sequenced and analyzed, with additional micromorphology of a lance nematode assessed in scanning electron micrographs (SEM). Soil samples were taken to a depth of 25 cm and stratified into 5 cm increments during April, June, August and October at seven sites across Missouri, three in the Kansas City metro of Kansas in 2021 and in ten sites across Indiana in 2022. Samples were stratified in five-centimeter increments and aggregated for a total of 100 cm3 of soil at each depth for each sampling. Samples were processed using a semi-automatic elutriator followed by the sucrose-flotation method, and populations were counted using a hemocytometer and recorded. For molecular characterization, rDNA was extracted and analyzed from 31 individual lance nematodes from one site in Missouri and eight sites in Indiana, and 13 root-knot nematodes from nine sites across Indiana. A significant interaction occurred between sampling month and depth for lance and ring nematodes Missouri/KS, with both PPN populations peaking at the 0-5 cm depth during October, which is well after most targeted nematicide applications are applied. Ring nematodes in Indiana did not follow this trend and were most abundant in August at a depth of 0-5 cm. No significant interaction between depth and month occurred for lance or root-knot nematodes in Indiana, or root-knot nematodes in Missouri/KS. Hoplolaimus stephanus and H. magnistylus were the lance species identified on golf greens, and Meloidogyne naasi, M. graminicola and M. marylandi were the root-knot species identified. Scanning-electron micrographs confirmed morphological characteristics unique to H. stephanus.

Population Dynamics of Mesocriconema xenoplax Parasitizing Sweet Cherry Trees in British Columbia, Canada.

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.

Occurrence of Plant-Parasitic Nematodes on Ornamental Foliage Plants, Citrus Orchards, and Tea Plantations in Korea

This study was conducted to investigate the plant-parasitic nematodes of ornamental foliage plants, citrus orchards, and tea plantations from July to December 2022. As a result of the investigation of plant-parasitic nematodes in 415 foliage plants, root-lesion nematodes were detected most frequently, followed by rootknot nematodes, pin nematodes, and other nematodes. In tea plantations, spiral nematodes, cyst nematodes, and root-knot nematodes were detected. Citrus nematodes, ring nematodes, and root-knot nematodes were discovered in citrus orchards. In foliage plants, tea plantations, and citrus orchards, the detection rate of plantparasitic nematodes was not high, but root-lesion nematodes were detected. Therefore, it is necessary to apply appropriate control methods to manage root-lesion nematodes during the cultivation of foliage, tea, and citrus plants.

Nematode population dynamics and plant steaming effects on strawberry cultivars under organic field conditions in Florida

Summary Demand for Florida organic strawberries has significantly increased in recent years, yet this industry is threatened by pests and pathogens that often come with transplants from out-of-state nurseries. Plant steaming has been explored as an alternative to reduce those threats in transplants. This study evaluated the yield performance of seven strawberry cultivars and their impact on nematode densities and plant vigour after steaming was applied to transplants imported from California during two growing seasons (2020-2021 and 2021-2022). The cultivars used were ‘Sensation® Florida127’, ‘Florida Brilliance’, ‘Florida Radiance’, ‘Winterstar™ FL 05-107’, ‘Florida Elyana’, ‘Strawberry Festival’ and ‘Florida Beauty’. Plant steaming reduced plant vigour only 4 weeks after transplanting. Nevertheless, no negative effect was observed in total fruit yield. Differences among cultivars were observed for plant vigour, total fruit yield and abundance of root-knot nematodes. The plant vigour of each cultivar depended on the time of the year, which varied significantly throughout the season. Cultivars ‘Sensation® Florida127’ and ‘Florida Radiance’ attained the highest total yield in both seasons. There was an effect of the cropping system in the nematode community, which increased the bacterivores but drastically reduced omnivores and ring nematodes over time. No effect of cultivar was observed in plant-parasitic nematode populations. The cultivar ‘Winterstar™ FL 05-107’ was an exception since Meloidogyne javanica population densities were significantly higher in ‘Winterstar™ FL 05-107’s experimental plots. Overall, transplant steaming shows the potential to be a component of an integrated pest and disease management programme for the success of sustainable and profitable yields

Vineyard soil texture and pH effects on Meloidogyne hapla and Mesocriconema xenoplax

AbstractNorthern root‐knot nematode (Meloidogyne hapla) and ring nematode (Mesocriconema xenoplax) are the most prevalent plant‐parasitic nematodes of wine grapes in the Pacific Northwest, but M. hapla is most important in eastern Washington and M. xenoplax in western Oregon. These regions differ edaphically where Washington soils are minimally weathered and alkaline while Oregon soils are highly weathered and acidic. To examine the effect of soil texture and pH on nematode reproduction, an alkaline, sandy loam soil (pH 7.9) from Washington and an acidic loam soil from Oregon (pH 5.4) were modified to the other pH extreme, and to a middle pH of 6.9. Tomatoes were planted into each soil/pH combination, and either 500 M. hapla second‐stage juveniles or M. xenoplax individuals were added to each pot. After 7 weeks, plants were harvested, three roots collected for analysis, remaining roots and leaves dried and weighed, and nematode population densities determined as eggs on roots (M. hapla) and nematodes in soil (M. xenoplax). Soil texture (sandy loam or loam) had no effect on either nematode, but M. hapla reproduction was greater in the lowest pH soil while M. xenoplax was unaffected by soil pH. Mesocriconema xenoplax parasitism reduced root length and root tip number, whereas M. hapla increased root mass in the highest pH Washington soil. Under these experimental conditions, it appears vineyard soil texture in the Pacific Northwest is not a determining factor in population growth of these nematodes, but M. hapla performed better at low pH.

Successional effects of cover cropping and deep tillage on suppression of plant-parasitic nematodes and soilborne fungal pathogens.

Cover crops can suppress soilborne nematodes and fungal pathogens by serving as a poor host to pathogens and producing allelopathic compounds. Yet, cultural practices can influence their effectiveness. Cover crop and weedy fallow rotations and their interactions with deep tillage were evaluated from 2019 to 2021 in a three-season vegetable cropping system (spring tomato, fall squash, and winter cabbage) for their suppressive effects on soilborne diseases. Experimental plots were arranged in a split-plot 2 × 4 factorial design in randomized complete blocks. Whole-plot tillage treatments were shallow-tilled or deep-tilled. Subplots had two factors of crop rotations: rotation type (cover crop [spring or fall sunn hemp or winter rye] or weedy fallow) and rotation season. Independent of tillage practice, sunn hemp and weedy fallow reduced population density and root galling severity of root-knot nematode (Meloidogyne incognita) for the first subsequent vegetable compared to the all-vegetable rotation (P < 0.05) but had little effect on fungal pathogens. Fall sunn hemp had higher plant biomass and reduced gall severity for the second subsequent vegetable. Spring and fall sunn hemp improved vegetable yields. Winter rye only reduced ring nematodes (Mesocriconema spp.) population density in the first subsequent vegetable. Deep tillage reduced incidence of fungal pathogens of Rhizoctonia solani and Sclerotinia sclerotiorum, and population density of stubby-root nematode (Nanidorus minor). Sunn hemp is effective in suppressing M. incognita, whereas deep tillage can be used to suppress R. solani, S. sclerotiorum, and N. minor in vegetable production systems. © 2023 Society of Chemical Industry.

First Report of Mesocriconema xenoplax from Apricots (Prunus armeniaca) in Ontario, Canada.

Plant-parasitic nematodes have been causing more economic losses and related damages to fruit crops in the Province of Ontario than previous estimates. We have been conducting surveys since 2019 for the presence of plant-parasitic nematodes in different orchards in the Niagara region. Collected soil samples were extracted for nematodes following Jenkins (1964). Among the plant-parasitic nematodes identified, we detected ring nematodes (Mesocriconema species) in 87% of the soil samples collected from different apricots fields, ranging from 20 to 200 ring nematode per kg of soil. The apricot cultivar was Haroblush and did not show any symptoms of nematode infestation. The morphometric measurements (mean in μm ± standard deviation, range) of the ring nematodes (adult females), n = 27), body length = (605 +/- 23, 550 - 650), stylet = (75 +/- 8, 65 - 79), a (total body length divided by maximum body diameter = 12 +/- 1.5, 10.2 - 13.9), b (total body length divided by pharyngeal length = 3.6 +/- 0.5, 3.2 - 3.9), c = 20, V (percentage of length from anterior end to vulva position in total body length) = 92 +/- 1.3,91 - 93), R (total body annules = 105 +/- 5, 100 - 110), Rvan (total annules between vulva and anus = 2), and Ran (total annules between anus and tail terminus = 5). Lips sclerotized, with conspicuous and elevated labial disc surrounding the oral aperture, sub-lateral lobes also conspicuous. The stylet was long and robust. Excretory pore was located between 30-31 annuli from the anterior end. The vulva located either between 6 and 7, but mostly between 7 and 8 annuli from the posterior end. The juveniles were similar to the females in body shape with: sub-lateral lobes present, stylet 55-60 µm long, total annuls 80-90, and fine longitudinal lines were observed. Based on the morphology (Figure 1) and morphometric characteristics, the nematode species was identified as Mesocriconema xenoplax, which was consistent with the description by Raski (1952). To further confirm, DNA was extracted from a total of 20 nematodes (females and juveniles), the D2-D3 expansion segment of 28S rDNA amplified using the primer pair: D2A: 5´-ACAAGTACCGTGAGGGAAAGT TG-3', D3B: 5'-TCCTCGGAAGGAACCAGCTACTA-3' (Nunn, 1992). The PCR product was purified and sequenced. The resulting sequence was deposited into the GenBank database and assigned with accession number ON130754. A BLAST search in the NCBI database revealed 99% similarity to sequences of M. xenoplax with accession numbers MH819082.1 and FN433854.1 from South Africa and California, respectively. Eight Haroblush plants were each inoculated with 100 ring nematodes/kg in 5-gallon pots. Haroblush without nematode were maintained as control. The nematode reproduction and symptoms were assessed after 6 and 24 months. The plants did not show below or aboveground symptoms after 6 months. However, root growth reduction, necrosis and death of feeder roots were observed after 24 months when compared to the control. Nematodes extracted from the soil had a mean of 512±48 and 1593±162 ring nematode/kg after 6 and 24 months, respectively, an indication of susceptibility. Mesocriconema xenoplax can cause 85% reduction in root biomass, and yield losses can occur at higher infestations (Pinkerton et al., 2004). Regardless, the potential impact and distribution of this nematode on apricots growth and yield in Ontario are not documented yet. To the best of our knowledge, this is the first report of the ring nematode M. xenoplax on apricots from Ontario, Canada.

A Blind-Identification Test on Criconema annuliferum (de Man, 1921) Micoletzky, 1925 Species Complex Corroborate the Hyper-Cryptic Species Diversity Using Integrative Taxonomy.

Ring nematodes are obligate ectoparasites on crops and natural herbaceous and woody plants, and some species are of economic importance and cause damage to roots of several crops. Recent integrative taxonomical analyses recognized the existence of two cryptic species within the Criconema annuliferum morphotype in Spain. In this study, we corroborated that morphometric, morphological and a multi-locus analysis (including the ribosomal markers D2-D3 expansion segments of 28S rRNA, ITS rRNA, 18S RNA, and the mitochondrial DNA cytochrome oxidase I gene) identified a new lineage clearly separated from C. annuliferum, C. paraannuliferum and C. plesioannuliferum. The new lineage was described herein as Criconema pseudoannuliferum sp. nov., confirming that C. annuliferum species complex species complex comprises a hyper-cryptic species complex. This research analysed soil samples from the rhizosphere of maritime pine (Pinus pinaster Ait.) forests in Bermeja-Crestellina Mountain, located at the western part of Málaga province, southern Spain. The integrative taxonomical analyses revealed the occurrence of a new cryptic species identified using females, males and juveniles with detailed morphology, morphometry and molecular markers, described herein as Criconema pseudoannuliferum sp. nov. All molecular markers (D2-D3, ITS, 18S and COI) were obtained from the same individual that was also used for morphological and morphometric analyses. This research demonstrated the hidden diversity within the C. annuliferum species complex species complex can reach to four lineages under ribosomal and mitochondrial gene markers for one morphospecies group, which includes four species, viz. C. annuliferum, C. paraannuliferum, C. plesioannuliferum, and C. pseudoannuliferum sp. nov. Criconema pseudoannuliferum sp. nov. was detected in moderate soil density in two maritime pine forests (5 and 25 nematodes/500 cm3 of soil) suggesting that does not cause damage to maritime pine.

Plant-Parasitic Nematodes Associated with Cannabis sativa in Florida.

The subtropical climate of Florida allows for a wide range of crops to be grown. With the classification of hemp (Cannabis sativa L., <0.3% delta-9-tetrahydrocannabinol) as an agricultural commodity, hemp has become a potential alternative crop in Florida. Hemp cultivars of different geographies (Europe, China, and North America), and uses (fiber, oil and CBD), were evaluated in three field experiments. The field experiments evaluated a total of 26 cultivars and were conducted for two consecutive seasons at three different locations (soil types) in North (sandy loam), Central (fine sand), and South Florida (gravelly loam). Nematode soil populations were measured at the end of each season. A diverse population of plant-parasitic nematodes was found, with reniform nematodes (RN, Rotylenchulus reniformis) the dominant species in North and South Florida (up to 27.5 nematodes/cc soil), and RKN (Meloidogne javanica) the main species in central Florida (up to 4.7 nematodes/cc soil). Other nematodes that were commonly found in south Florida (and to a lesser extent north Florida) were spiral (Helicotylenchus spp.), stunt (Tylenchorhynchus spp.) and ring nematodes (Criconemoids), while in central Florida, stubby root (Nanidorus minor) and sting nematodes (Belonolaimus longicaduatus) were found. No significant difference among hemp cultivars was noted at any of the locations. RKN were found in all three regions and soils, while RN were only found in North and South Florida. This is the first report on plant-parasitic nematodes associated with hemp in Florida fields. Natural nematode populations varied greatly, depending on where in Florida hemp was grown. Growers who wish to include hemp in their crop rotation need to be aware of potential pest pressure from nematodes. More research is needed to determine to what extent nematodes, especially RKN and RN, can reduce hemp growth and yield.

On-Farm Evaluations of Nonfumigant Nematicides on Nematode Communities of Peach.

Experiments were established to evaluate the efficacy of currently available nonfumigant chemical and biological nematicides against nematode communities in peach orchards in two different geographic regions of South Carolina: the Upstate and Ridge. The treatments included sole or mixed application of two chemical nematicides (oxamyl and fluopyram) and a biological nematicide (Majestene) plus an untreated control. Ring nematode and lesion nematode were predominant in Upstate and Ridge orchards, respectively. Fluopyram was the most effective nematicide in the Upstate orchard, and it reduced plant-parasitic nematodes by 69% relative to the untreated control at 3months postapplication. Similarly, fluopyram and oxamyl suppressed 74 to 87% of plant-parasitic nematodes in the Ridge orchard at 2months postapplication. Significant effects of Majestene on plant-parasitic nematodes was not observed. Mixed applications of nematicides were also effective in suppressing plant-parasitic nematodes although the suppressions were not always significant from sole applications or the control. The chemical nematicides significantly reduced free-living nematodes in the first 2months following their applications in the Ridge orchard, the reductions ranging from 60 to 79% relative to the control. However, free-living nematode populations quickly rebounded to the highest level in 3months following the nematicide applications. Free-living nematode communities in the Upstate orchard did not experience any significant effects of nematicides until 4 months following nematicide application; at that time there was a 60 to 68% decline in populations. Results from this study suggest that the nonfumigant nematicides can only provide a short-term management of plant-parasitic nematodes in peach.

A Proposed New Species Complex within the Cosmopolitan Ring Nematode Criconema annuliferum (de Man, 1921) Micoletzky, 1925.

Ring nematodes are obligate ectoparasites on cultivated and wild herbaceous and woody plants, inhabiting many types of soil, but particularly sandy soils. This study explored the morphometrical and molecular diversity of ring nematodes resembling Criconema annuliferum in 222 soil samples from fruit crops in Spain, including almond, apricot, peach and plum, as well as populations from cultivated and wild olives, and common yew. Ring nematodes of the genus Criconema were detected in 12 samples from under Prunus spp. (5.5%), showing a low to moderate nematode soil densities in several localities from southeastern and northeastern Spain. The soil population densities of Criconema associated with Prunus spp. ranged from 1 nematode/500 cm3 of soil in apricot at Sástago (Zaragoza province) to 7950 and 42,491 nematodes/500 cm3 of soil in peach at Ricla and Calasparra (Murcia province), respectively. The integrative taxonomical analyses reveal the presence of two cryptic species identified using females, males (when available), and juveniles with detailed morphology, morphometry, and molecular markers (D2-D3, ITS, 18S, and COI), described herein as Criconema paraannuliferum sp. nov. and Criconema plesioannuliferum sp. nov. All molecular markers from each species were obtained from the same individuals, and these individuals were also used for morphological and morphometric analyses. Criconema paraannuliferum sp. nov. was found in a high soil density in two peach fields (7950 and 42,491 nematodes/500 cm3 of soil) showing the possibility of being pathogenic in some circumstances.

Plant-parasitic nematodes in Nova Scotia vineyards

Plant-parasitic nematode populations were analyzed from composite soil samples collected from 62 vineyard blocks throughout Nova Scotia in 2018 and 2019. Nematode groups of potential concern that were found included ring nematodes (family Criconematidae), dagger nematodes (Xiphinema spp.), and root-knot nematodes (Meloidogyne spp.). Ring nematodes were overall the most widespread and abundant group of plant-parasitic nematodes, recovered from 79% of blocks with an overall average population density of 114 nematodes per 100 cm3 soil. Ring nematodes tended to be more abundant in older blocks. DNA sequence analyses of a subset of the ring nematode populations confirmed the presence of Mesocriconema xenoplax, which is the species known to be damaging to and most widely associated with grapevine globally. The analyses indicated that Criconema permistum was also present, notably in samples with the greatest ring nematode population densities. The results indicate that ring nematodes could be affecting the health of Nova Scotia vineyards, particularly in the future as populations continue to develop in relatively young vineyards and as older blocks are replanted. Additional research is needed to delineate the distribution of M. xenoplax vis-à-vis other species and to experimentally assess the host-parasite relationship between C. permistum and grapevine.

Biosolarization restructures soil bacterial communities and decreases parasitic nematode populations

Biosolarization is a soil disinfestation technology that combines passive solar heating and organic amendments to generate multiple pest-inactivating stressors. The objectives of this study were to assess the performance of almond (Prunus dulcis) processing residues in biosolarization to control infestations of root lesion (Pratylenchus vulnus) and ring nematodes (Mesocriconema xenoplax) during the pre-planting period of an almond orchard. The broader effects on soil microbial community composition were assessed by 16S rRNA gene sequencing immediately before and after biosolarization, as well as two months after treatment ended. Soil organic acids with nematicidal activity peaked after 9 days in biosolarized plots. Temperatures in biosolarized plots and solarized control plots reached maximum values 9–12 °C higher than untreated control plots. Biosolarization and solarization also enriched for specific Firmicutes, Actinobacteria, and Proteobacteria taxa associated with nematode suppression, some of which remained enriched two months post treatment. Biosolarization led to 100% mortality of P. vulnus in the upper 0–30 cm soil layer by 9 days of treatment. In contrast, reductions in plant-parasitic nematode densities between non-amended, solarized treatments and untreated controls were not observed until day 41 of treatment.

Integrative taxonomy of Mesocriconema onoense (Tylenchida: Criconematidae) from Vietnam highly suggests the synonymization of Mesocriconema brevistylus and related species.

The genus Mesocriconema is one of the most diverse genera within the family Criconematidae, known as ring nematodes, with more than 90 species. Although species in this genus usually show distinct morphological characterizations, the identification based only on morphology can lead to misidentification in many studies resulted in a number of synonymizations in the genus over time. In this study, an integrated approach has been applied in characterizing Mesocriconema onoense from Vietnam. The molecular data of 28S rRNA, ITS, 18S rRNA regions were analyzed and discussed to confirm the correct names on GenBank. Besides, phylogenetic analyses of 28S rRNA, ITS, and 18S rRNA regions of Mesocriconema species revealed that Mesocriconema brevistylus should be considered as a junior synonym of M. onoense. Consequently, M. helicus, M. onostris, and M. paronostris should also be considered as the synonyms of M. onoense.

Real time PCR assays to detect and quantify the nematodes Pratylenchus vulnus and Mesocriconema xenoplax

Economically damaging populations of lesion nematode and ring nematode are managed in tree crops largely through pre-plant chemical fumigation, the use of which is increasingly restricted due to human health and environmental concerns. Reducing the use of fumigants requires precise knowledge of pest nematodes’ density and distribution, however; extensive sampling is costly due to the time intensive process of nematode counting and identification. In this study, species specific primers were designed and real time PCR (qPCR) assays developed separately for both species of nematodes. The assays successfully detected each species and did not show significant amplification of non-target nematode groups. Both assays related well with microscopic counts of prepared solutions of nematodes, as well as solutions extracted from field samples. Such high-throughput molecular quantification could reduce diagnostic costs, allowing a more accurate picture of nematode populations in the field.

Bionematicides as an alternative to methyl bromide fumigation.

Fumigant use in perennial crops can be reduced through prolonging the life of existing orchards. The longer an orchard remains healthy and productive, the less often it will be terminated, fumigated, and replanted. Two trials were conducted to determine the effectiveness of DiTera, a toxin produced by the fungus (Myrothecium verrucaria) and Nema-Q, an extract of the soap bark tree (Quillaja saponaria) for management of root-lesion (Pratylenchus vulnus) and ring (Mesocriconema xenopla) nematodes on walnuts. In the first trial, spring and fall treatments of DiTera were applied each year for four years to variety ‘Chandler’ scion on seedling ‘Paradox’ rootstock, and to own-rooted ‘Chandler’ trees. On ‘Paradox’ rootstock, both DiTera and Nema-Q increased walnut yields (P ≤ 0.05) and produced more vigorous trees (P ≤ 0.05) without significant reductions in nematode populations (P ≤ 0.05). A second trial was conducted with three rates of DiTera and four rates of Nema-Q, combinations of the two products, and an untreated control on ‘Chandler’ scion on ‘Paradox’ rootstock. The highest rate of Nema-Q (P ≤ 0.05), and a combination treatment of DiTera plus Nema-Q (P ≤ 0.05) increased trunk circumference. Several treatments showed reductions in root-lesion and ring nematodes (P ≤ 0.05). Bionematicides can improve yield, growth, and vigor in walnut orchards infested with plant-parasitic nematodes.