Lesion Nematode Populations Research Articles

Evaluating the densities and distribution of root-lesion nematodes (Partylenchus spp.) in wheat grown in Canterbury, New Zealand

Species of root-lesion nematode (Pratylenchus spp.) are associated with significant reductions in wheat yield in wheat-growing regions around the world. Of these, Pratylenchus thornei and P. neglectus are known to cause the highest damage to the Australasian wheat industry. New Zealand is known to produce high wheat yields on a per-hectare basis yet little research has been conducted to date to determine the effects of Pratylenchus spp. on the production of wheat in New Zealand. Therefore, as the first step towards filling this knowledge gap, the current research focused on conducting surveys to determine the population densities and distribution of Pratylenchus spp. in wheat-growing regions in Canterbury, South Island, New Zealand. Surveys were conducted at ten selected sites that were geographically distinct from each other. At six of the ten sites, lesion nematode populations were reported to be above the recorded Australian threshold of 2000 nematodes per kg of soil. In Australia, it’s been recorded that around 50% yield reductions can occur in intolerant wheat varieties when population densities reaches this number. Differences in population density within each location was also observed indicating the uneven distribution of lesion nematodes within a field. Morphological measurements of the nematodes collected from multiple sites during this study confirmed the presence of P. thornei and P. neglectus in Canterbury wheat-producing areas indicating a potential threat to the New Zealand wheat industry by root-lesion nematodes. Further studies need to be conducted to fully understand the situation and to develop management strategies to mitigate threats from nematodes.

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.

Canola versus wheat rotation effects on subsequent wheat yield

Winter canola (Brassica napus L.) (WC) is considered the most promising oilseed crop for diversifying wheat (Triticum aestivum L.)-based cropping systems in the Inland Pacific Northwest, USA (PNW). Canola serves as a break or non-host crop for many important soilborne pathogens of wheat and helps farmers control weeds. Most studies in the literature report that canola has a positive effective on subsequent wheat yield. We conducted a 6-yr field experiment near Davenport, WA to measure the effects of WC versus winter wheat (WW) on the subsequent production of spring wheat (SW). Averaged over the years, there were no differences between WC and WW in soil water use or overwinter water recharge into the soil following these crops. Subsequent SW had excellent plant stands, was weed free, was adequately fertilized, and had no foliar or root diseases. Root lesion nematode populations were miniscule and insignificant. Average SW seed yield following WC was 3292 kg/ha versus 3897 kg/ha following WW; a 17% reduction (p < 0.0001). Visual differences in SW plant height and spike density between treatments were also apparent. Spring wheat grain yield differences could not be attributed to the variables measured. This study provides novel information for ongoing efforts to promote and expand canola production and the influence of brassica crops on the subsequent performance of wheat.

Contribution of a Winter Wheat Cover Crop to the Maintenance of Root Lesion Nematode Populations in the Red Raspberry Production System

One of the primary production challenges red raspberry (Rubus idaeus) growers in the Pacific northwestern United States confront is root lesion nematode [RLN (Pratylenchus penetrans)]. In this perennial production system, red raspberry serves as a sustained host for RLN. When a red raspberry planting is slated for removal in the fall, a new red raspberry planting quickly follows in the same field the following spring. The primary crop that occurs in rotation with red raspberry is a winter wheat cover crop to provide soil coverage and protection during the winter. The objectives of this research were to determine if winter wheat (Triticum aestivum) provides a green bridge for RLN in continuous red raspberry production systems and to determine if modified winter cover cropping practices can be used to reduce population densities of RLN before replanting red raspberry. Four trials were established in fields being replanted to red raspberry and the following modified winter cover cropping practices were considered: cover crop planting date (at fumigation or 2 weeks after fumigation), termination date (cover crop kill with herbicide 2 or 6 weeks before incorporation compared with the industry standard of incorporation immediately before planting), and the additional application of methomyl. ‘Rosalyn’ and ‘Bobtail’ winter wheat planted as cover crops in these trials were demonstrated to be maintenance hosts for RLN (ranging from 10 to 947 RLN/g winter wheat root across trials) allowing them to be a green bridge for RLN to infect the following red raspberry crop. Altering winter wheat cover crop planting date, termination date with herbicide, or methomyl application did not affect RLN population densities in the subsequent red raspberry crop. Although planting an RLN maintenance host may be of concern to growers, the advantages of reduced soil erosion and nitrate leaching associated with cover cropping outweigh the perceived risk to the subsequent red raspberry crop.

First Report of Pratylenchus neglectus on Winter Wheat in China.

Root-lesion nematodes are major pathogens of wheat and have been reported in the United States, Mexico, India, Australia, Egypt, Canary Islands, South Africa, Iran, Japan, the Netherlands, Belgium, Italy, Germany, and Yugoslavia (1). They can also cause injury in a large number of crops, including grasses, cereal grains, and vegetables. In 2009 and 2010, a survey was conducted for nematodes in winter wheat fields near Taian city, Shandong, northern China. Root tissues were stained via the acid fuchsin tissue stain technique, and nematode numbers were recorded under a stereo microscope. Sixty-eight root samples were collected during the winter wheat growing season, and root lesion nematode was found in all samples. The highest average lesion nematode populations in fresh roots were 154.3 nematodes/g in 2009 and 236.7 nematodes/g in 2010. Nematodes were collected from infested wheat roots by a modified Baermann funnel method. Dimensions of the nematodes were: length, 0.42 to 0.54 mm; a, 18.8 to 24.2; b, 4.4 to 5.7; c, 19.8 to 25.4; V, 80.4 to 84.8; and spear, 17.1 to 18.9 μm. DNA was extracted from individual nematodes using liquid nitrogen. Amplification of rDNA-internal transcribed spacer region using the forward primers 5'-CGTAACAAGGTAGCTGTAG-3' and the reverse primer 5'-TTTCACTCGCCGTTACTAAGG-3' yielded a PCR fragment of approximately 900 bp. PCR products were purified using Universal Plant DNA Purification Kit (Tiangen, China) and ligated to the pMD18-T vector system (TaKaRa Bio, Japan) and transformed to E. coli strain DH5α. Plasmid DNA carrying the insert was extracted and used as the template for DNA sequencing. DNA sequencing was carried out in an ABI 3730, compared and aligned using MEGA 5.0. Sequences showed 96% sequence identity with those of Pratylenchus neglectus (GenBank Accession No. FR692291.1). The sequence was submitted to the GenBank database (JX228136). To our knowledge, this is the first report of P. neglectus infesting winter wheat in China. P. neglectus has been reported as causing economically significant damage to wheat production of up to 70% yield loss in the Pacific Northwest. Damage from lesion nematode may therefore be potentially significant to wheat production in Shandong Province, and further information should be obtained on its prevalence.

Interaction of Brassicaceous Seed Meal and Apple Rootstock on Recovery of Pythium spp. and Pratylenchus penetrans from Roots Grown in Replant Soils.

Pythium spp. and Pratylenchus penetrans are significant components of the diverse pathogen complex that incites apple replant disease in Washington State. The structure of the Pythium population differs among orchard soils but is composed of multiple pathogenic species. Studies were conducted to determine the effect of brassicaceous seed meals and apple rootstock on the activity and composition of these pathogen populations. Brassicaceous seed meals differed in capacity to suppress Pythium numbers and apple root infection, as well as differentially transformed composition of the population recovered from apple roots. Brassica juncea seed meal (SM) was the sole seed meal examined to suppress Pythium numbers and root infection; however, a persisting population was always detected in which Pythium irregulare existed as the dominant or co-dominant species. In general, the Geneva series rootstocks were less susceptible to root infection by native populations of Pythium, whereas M26, MM106, and MM111 were highly susceptible. Apple rootstocks from the Geneva series consistently supported lower populations of P. penetrans than did Malling or Malling-Merton rootstocks. B. juncea SM was superior to Brassica napus SM or Sinapis alba SM in suppressing lesion nematode populations. Significant rootstock × seed meal interaction was detected, and nematode suppression in response to B. napus or S. alba SM was only observed when used in concert with a tolerant rootstock, while B. juncea SM suppressed lesion nematode root populations irrespective of rootstock. These findings demonstrate that utilization of brassicaceous seed meal amendments for replant disease suppression must employ an appropriate rootstock in order to achieve optimal disease control.

Pratylenchus neglectus, P. thornei, and Paratylenchus hamatus Nematodes Causing Yield Reduction to Dryland Peas and Lentils in Idaho.

In June 2006, stunted and chlorotic plants were observed in large patches in two 40.5-ha fields of dryland peas (Pisum sativum) in Latah County, Idaho, which resulted in 90 and 75% crop loss. In the same region, a 121.4-ha field of dryland lentils (Lens culinaris) also had plants showing poor growth, wilting, and yellowing in large patches, which resulted in 40% crop loss. Two species of lesion nematodes (Pratylenchus neglectus and P. thornei) and one species of pin nematode (Paratylenchus hamatus) were extracted from rhizosphere soil and the roots of symptomatic plants from these fields. In a subsequent survey of seven dryland pea fields, under cv. Columbian, in Latah and Nez Perce counties and one dryland pea field, under cv. Small Sieve, in Latah County, plant samples had means of 551 and 2,178 mixed species of lesion nematodes per gram of dry root, respectively. Plant samples from 12 lentil fields in Latah County, six planted with cv. Red Chief and six with cv. Pardina, had means of 279 and 987 mixed species of lesion nematodes per gram of dry root, respectively. Soil samples from the same fields had a mean of 628 and 671 pin nematodes, Paratylenchus hamatus, per 250 cm3 soil for Red Chief and Pardina, respectively. Lentils cv. Pardina and peas cv. Columbian were planted separately in six pots, five seeds per pot containing 250 g of infested soil brought from the field to the greenhouse. Fumigated sandy loam soil was used as control. These assays were repeated three times. In addition, peas and lentils were planted to pots infested singly with each of the three nematode species. For this assay, nematodes were extracted from field soil, surface sterilized, and used to infest 250 g of fumigated sandy loam soil at two nematodes per gram of soil. Six plants per nematode species and an uninoculated control were used in the greenhouse assays, which were repeated three times. Nematodes in all of the assays reduced plant growth in comparison with controls; an average of 50 to 70% reduction in plant height was noted. The lesion nematode populations increased in all pots. The greenhouse assays verified the negative impact of these nematodes on growth of dryland peas cvs. Columbian and Small Sieve and lentils cvs. Red Chief and Pardina. P. neglectus, P. thornei, and Paratylenchus spp. previously have been reported from the semi-arid Pacific Northwest (1). However, to our knowledge, this is the first report attributing plant growth and yield reduction of certain cultivars of lentils and peas to these two species of lesion nematodes and pin nematodes, identified to species level as Paratylenchus hamatus. Reference: (1) R. W. Smiley et al. J. Nematol. 36:54, 2004.

The impact of farming systems on soil biology and soilborne diseases: examples from the Australian sugar and vegetable industries – the case for better integration of sugarcane and vegetable production and implications for future research

A sugarcane farming system based on residue retention, minimum tillage, a leguminous rotation crop and controlled traffic using global positioning system guidance is currently being adopted by the Australian sugar industry because it improves sugar yields, reduces costs and provides additional income from crops such as soybean and peanut. This paper discusses the soil health improvements that are being obtained with this new farming system, particularly its beneficial effects on soil carbon levels and soil biological properties. It also summarises research showing that breaking the sugarcane monoculture with a soybean or peanut crop reduces populations of lesion nematode (Pratylenchus zeae) and root-knot nematode (Meloidogyne javanica), the two most important nematode pests of sugarcane. The role of minimum tillage and inputs of organic matter in enhancing the natural biological control mechanisms that suppress these nematodes is also discussed. The paper then considers the farming system currently used for vegetable crops such as tomato, capsicum and rockmelon, where inadequate crop rotation, excessive tillage, low organic inputs and the fallowing and solarisation effect of covering beds with plastic leads to a situation where soil fumigation is seen as the only option for reducing losses from soilborne pests and pathogens. Since the sugar industry coexists with the vegetable industry in some areas of Australia, the paper argues the case for developing minimum tillage practices for vegetable production and integrating them into the sugarcane farming system. It concludes that a farming system of this nature would improve profitability in both industries, produce better environmental outcomes at a landscape level and provide more sustainable solutions to nematode and soilborne disease problems.

Oriental mustard bran reduces Pratylenchus penetrans on sweet corn

Oriental mustard bran (Brassica juncea) is a by-product of the mustard-milling process. Its nematicidal activity has been confirmed in vitro and in the greenhouse in a previous study. In the present study, two field trials were undertaken in 1997 and 1998 to evaluate the potential of the bran to reduce populations of the root-lesion nematode Pratylenchus penetrans on sweet corn. When incorporated into the soil to a depth of 15 cm, the bran, applied at the rate of 1120 kg/ha (1000 lb/acre), significantly enhanced the growth of sweet corn as manifested by an increase in root biomass and marketable yield in both trials. However, the effects on nematode populations were inconsistent between the two trials. In 1997, bran applied at 1120 kg/ha significantly reduced the population density of lesion nematodes in the soil. However, in 1998 no significant reduction in lesion nematode populations in bran treatments was observed. Key words: Brassica juncea, isothiocyanates, lesion nematode, mustard bran, nematicide, Pratylenchus penetrans, sweet corn. Le son de la moutarde brune (Brassica juncea) est un sous-produit du procédé de mouture de la moutarde. Son action nématicide a été vérifiée in vitro et en serre lors d'une étude antérieure. Dans l'étude ici rapportée, deux essais en champ ont été entrepris en 1997 et en 1998 afin d'évaluer la capacité du son à diminuer les populations de Pratylenchus penetrans sur le maïs sucré. Lorsqu'il a été enfoui dans le sol à une profondeur de 15 cm, le son à 1120 kg/ha (1000 lb/acre) a significativement amélioré la croissance du maïs sucré dans les deux essais avec des augmentations de la biomasse racinaire et du rendement commercialisable. Cependant, les effets sur les populations de nématodes des essais de 1997 et 1998 ont été contradictoires. En 1997, le son à 1120 kg/ha a significativement réduit, dans le sol, la densité de population des nématodes des lésions. Cependant, en 1998, nous n'avons pas observé de réduction significative des populations de nématodes des lésions avec des traitements avec le son. Mots-clés : Brassica juncea, isothiocyanates, nématode des lésions, son de moutarde, nématicide, Pratylenchus penetrans maïs sucré.

The role of plant-parasitic nematodes in reducing yield of sugarcane in fine-textured soils in Queensland, Australia

Damage to sugarcane caused by root-knot nematode (Meloidogyne spp.) is well documented in infertile coarse-textured soils, but crop losses have never been assessed in the fine-textured soils on which more than 95% of Australia’s sugarcane is grown. The impact of nematodes in these more fertile soils was assessed by repeatedly applying nematicides (aldicarb and fenamiphos) to plant and ratoon crops in 16 fields, and measuring their effects on nematode populations, sugarcane growth and yield. In untreated plant crops, mid-season population densities of lesion nematode (Pratylenchus zeae), root-knot nematode (M. javanica), stunt nematode (Tylenchorhynchus annulatus), spiral nematode (Helicotylenchus dihystera) and stubby-root nematode (Paratrichodorus minor) averaged 1065, 214, 535, 217 and 103 nematodes/200 mL soil, respectively. Lower mean nematode population densities were recorded in the first ratoon, particularly for root-knot nematode. Nematicides reduced populations of lesion nematode by 66–99% in both plant and ratoon crops, but control of root-knot nematode was inconsistent, particularly in ratoons. Nematicide treatment had a greater impact on shoot and stalk length than on shoot and stalk number. The entire community of pest nematodes appeared to be contributing to lost productivity, but stalk length and final yield responses correlated most consistently with the number of lesion nematodes controlled. Fine roots in nematicide-treated plots were healthier and more numerous than in untreated plots, and this was indicative of the reduced impact of lesion nematode. Yield responses averaged 15.3% in plant crops and 11.6% in ratoons, indicating that nematodes are subtle but significant pests of sugarcane in fine-textured soils. On the basis of these results, plant-parasitic nematodes are conservatively estimated to cost the Australian sugar industry about AU$82 million/annum.

Influence of previous crops and nematicide treatments on root lesion nematode populations and crop yields

A field study assessing the influence of the previous crop, the crop sequence, and aldicarb treatments on root lesion nematode populations and crop yields was carried out in Prince-Edward-Island, Canada. The most recent crop had the greatest impact on nematode numbers. The crop sequences had an influence in some cases on root lesion nematode populations (primarily Pratylenchus penetrans) and on crop yields. In commercial barley (Hordeum vulgare) fields, root lesion nematodes in roots were greatest when barley followed a red clover (Trifolium pratense) timothy (Phleum pratense) ley, and stunt nematodes (Tylenchorhynchus spp., primarily T. dubius, and Merlinius spp.) were more common when barley followed barley. The combined dry weight of foliage and grain was larger when barley was planted after potato (Solanumtuberosum) and smaller when barley followed barley or a red clover-timothy mixture. Under experimental field conditions, root lesion nematode populations were largest in barley roots when barley followed potato and grain yields were smallest when barley followed barley. Changes in nematode populations in potato were not associated with crop sequences. Potato tuber yields were higher in the sequences that began with wheat (Triticum aestivum) or barley than in the sequences that began with potato or soybean (Glycine max). Aldicarb reduced the numbers of root lesion nematodes in roots with concomitant yield increases in potato and soybean.

Transformation of Soil Microbial Community Structure and Rhizoctonia-Suppressive Potential in Response to Apple Roots

ABSTRACT Changes in the composition of soil microbial communities and relative disease-suppressive ability of resident microflora in response to apple cultivation were assessed in orchard soils from a site possessing trees established for 1 to 5 years. The fungal community from roots of apple seedlings grown in noncultivated orchard soil was dominated by isolates from genera commonly considered saprophytic. Plant-pathogenic fungi in the genera Phytophthora, Pythium, and Rhizoctonia constituted an increasing proportion of the fungal community isolated from seedling roots with increasing orchard block age. Bacillus megaterium and Burkholderia cepacia dominated the bacterial communities recovered from noncultivated soil and the rhizosphere of apple seedlings grown in orchard soil, respectively. Populations of the two bacteria in their respective habitats declined dramatically with increasing orchard block age. Lesion nematode populations did not differ among soil and root samples from orchard blocks of different ages. Similar changes in microbial communities were observed in response to planting noncultivated orchard soil to five successive cycles of 'Gala' apple seedlings. Pasteurization of soil had no effect on apple growth in noncultivated soil but significantly enhanced apple growth in third-year orchard block soil. Seedlings grown in pasteurized soil from the third-year orchard block were equal in size to those grown in noncultivated soil, demonstrating that suppression of plant growth resulted from changes in the composition of the soil microbial community. Rhizoctonia solani anastomosis group 5 (AG 5) had no effect on growth of apple trees in noncultivated soil but significantly reduced the growth of apple trees in soil from third-year orchard soil. Changes in the ability of the resident soil microflora to suppress R. solani AG 5 were associated with reductions in the relative populations of Burkholderia cepacia and Pseudomonas putida in the rhizosphere of apple.

Pratylenchus Loosi From Pasture Grasses in Central Florida

Amphimictic populations of lesion nematodes with two lip annuli were detected from pasture grasses, Paspalum notatum and Panicum hemitomon, in central Florida. When cultured on carrot disks, these Pratylenchus species differed (P = 0.05) from P. coffeae cultures with respect to posterior uterine sac length (28 and 34.5 μm vs 53.5 μm), vulva % (77.5 and 77.4 vs 79.7), b (5.4 and 6.01 vs 6.4) and c (17 and 17.3 vs 21.3) ratios and shape of tail (narrowly rounded vs bluntly rounded, truncate or indented). Morphometric differences between these lesion nematode populations and P. coffeae tended to be greater when collected directly from their original hosts (grasses and citrus) than from carrot cultures. Morphological characters of Pratylenchus species from grasses were similar to those of P. loosi. The lesion nematodes from grasses, however, had females with more anterior vulva (76-79) than P. loosi paratypes (79-85) from Sri Lanka.

Management of lesion nematode (Pratylenchus jordanensis) on replanted apple trees

Chemical and non-chemical strategies for managing lesion nematode (Pratylenchus jordanensis) on apple replants were investigated in field experiments at Applethorpe, Queensland. In the first experiment, old trees from a nematode-infested orchard were removed in June 1987 or April 1988. Plots then received one of the following treatments: solarisation; fallow; animal manures (� 900 kg urea/ha); green manure crops of forage sorghum or lablab bean ploughed in (� 1800 kg urea/ha); ethylene dibromide or methyl bromide. Lesion nematode populations before replanting apple trees in July 1988 were generally lower if trees had been removed 12 months rather than 3 months previously. Nematodes increased on forage sorghum, but populations were reduced substantially when the crop was ploughed in with urea. Methyl bromide was the only treatment to reduce nematode populations at planting to very low levels. Two years after planting, nematode populations on apples were reduced by some of the chemical and non-chemical treatments. Most non-chemical treatments increased the growth of replanted apple trees, but methyl bromide produced the largest trees. In a second experiment, methyl bromide again enhanced early growth, but after 5 years, trees mulched with sawdust or sawdust and manure had the lowest nematode populations and produced yields as good as, or better than, methyl bromide. The results of both experiments suggested that lesion nematodes on apple replants could be managed without fumigant nematicides through a combination of early removal of the previous orchard, incorporation of animal manure or a green manure crop with urea, choice of an appropriate rootstock, and maintenance of a layer of organic mulch around trees.

Influence of aldicarb on root lesion nematodes, leaf disease and root rot in wheat and barley

The effects of aldicarb on populations of root lesion nematodes (primarily Pratylenchus penetrans) and on grain yields of spring barley and wheat were examined in the field over 3 years, 1981*83. The incidence of barley net blotch (Pyrenophora teres), wheat leaf blotch (Leptosphaeria nodorum), and common root rot (Cochliobolus sativus) was also recorded in 1982 and 1983. Aldicarb treatments reduced the size of root lesion nematode populations in soil and roots in all years, except in the mid‐season soil sample in 1983. The severity of leaf disease was decreased only in 1982, but the incidence of root rot was not significantly affected by the nematticide. Although aldicarb increased cereal grain yields by approximately 15% there was no significant relationship between numbers of root lesion nematodes in roots and soil and fungal disease symptoms on barley and wheat.

Effect of Post-plant Nematicides and Trickle Irrigation on Newly Planted Peach Trees1

Abstract Carbofuran (2,3-dihydro-2,2-dimethyl-7 benzofuranyl methylcarbamate) at 5.7 and 11.1 kg/ha reduced soil populations of lesion (Paratylenchus penetrans, Filipjev &amp; Shuurmans Stekhoven), pin (Paratylenchus sp. Cobb), and lance (Hoplolaimus galeatus, Cobb, Filipjeu &amp; Schuurmans Stekhoven) nematodes. The highest rates of granular and flowable carbofuran were phytotoxic on peach [Prunus persica (L.) Batsch] planted just prior to treatment. In a subsequent experiment in soil previously planted to peach (old soil) or not previously planted to peach (new soil), trickle irrigation alone reduced dagger (Xiphinema americanum, Cobb) and lesion nematode populations. Carbofuran plus trickle irrigation reduced the dagger and lesion nematode populations and had the highest rate of tree growth in the old soil. Granular phenamiphos (ethyl-3-methyl-4-(methylthio) phenyl (1-methylethyl) phosphoridate) either alone or in combination with trickle irrigation reduced the stunt (Tylenchorhynchus claytoni, Steiner) nematode population. However, when phenamiphos was applied alone, tree growth was equal to the control in old soil but less than the control in new soil.