Root-lesion Nematode Populations Research Articles

Prevalence of Verticillium spp. and Pratylenchus spp. in Commercial Potato Fields in Atlantic Canada

A survey of New Brunswick (NB) and Prince Edward Island (PEI) potato fields in crop rotation phase prior to potato production was conducted in fall (October and November) between 2017 and 2021. A total of 113 and 126 fields for NB and PEI, respectively, were surveyed with 20 to 35 fields each year tested in each province. Root lesion nematodes (RLN, Pratylenchus spp.) were detected in 99 and 98% of the fields for NB and PEI, respectively, and two root lesion nematode species, P. crenatus and P. penetrans, were identified in both provinces from 2017 to 2021. Based on 2019 and 2020 results, all surveyed fields in NB and PEI were detected with P. crenatus, while only 29 and 43% of the fields in NB and PEI were detected with P. penetrans, respectively. P. crenatus accounted for 96 and 89% of the populations for NB and PEI, respectively, while P. penetrans accounted for 4 and 11% in commercial fields, respectively. In a single in-depth sampled experimental field with a history of severe potato early dying complex in 2018 in NB, P. crenatus accounted for 88% and P. penetrans was 12%. Verticillium dahliae was detected in 94 and 92% of potato fields in NB and PEI, respectively. All isolates obtained from potato cv. “Russet Burbank” in a baiting trial were V. dahliae, belonging to two lineages. V. albo-atrum was detected in a few fields at very low level, except two fields in NB where V. albo-atrum was predominating over V. dahliae. Rotation crops did not affect V. dahliae population densities for NB and PEI, and did not affect RLN population in NB, but significantly affected RLN in PEI. Fall green cover crop did not affect the populations of RLN and V. dahliae in PEI. The present study revealed that the potato pathogenic root lesion nematode P. penetrans was present in less than 50% of surveyed fields and accounted for around 10% of root lesion nematode population in NB and PEI, and V. dahliae was the dominant species and was present in greater than 90% of surveyed fields in both provinces.

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.

Molecular and Morphological Characterization of The Root -lesion Nematode, Pratylenchus Neglectus, on Corn from Henan Province of China.

SummaryRoot-lesion nematodes, Pratylenchus spp., are economically important pathogens because of their detrimental and economic impact on a wide range of crops. In August 2018, two samples of both roots and rhizosphere soil were collected from a corn field in Liangyuanqu of Shangqiu city, Henan Province, China. Root-lesion nematodes were recovered from the roots and soil samples using the modified Baermann funnel extraction method. Both the morphological characters and molecular analysis of the internal transcribed spacer (ITS) and D2-D3 expansion region of 28S ribosomal RNA sequences confirmed that the root-lesion nematode population collected from corn in this study was P. neglectus. Phylogenetic analyses showed that this isolate formed a highly supported clade with other P. neglectus isolates. To the best of our knowledge, this is the first report of P. neglectus on corn in Henan Province of China. This study reports the first partial sequences of 28S D2-D3 region of P. neglectus on corn in China. Due to the great harmfulness of root-lesion nematodes to corn, care should be taken to prevent the spread of P. neglectus to other regions in China. At the same time, further study on the biological characteristics of P. neglectus is needed, which will be helpful to develop corresponding management and control strategies.

Occurrence of Pratylenchus coffeae Causing Root Rot of Soybean in Shandong Province of China.

Soybean (Glycine max L.) is a very important commercial crop in China (Li et al. 2019). Pratylenchus coffeae (Zimmermann, 1898) Filipjev & Schuurmans Stekhoven, 1941, is one of the most important root-lesion nematodes that invade the roots of many crops. In August 2018, five root and soil samples were collected in a soybean field, near Xipan village in Linshu county of Linyi City, Shandong Province, China (Fig. S1), to investigate the occurrence of root-lesion nematodes. The collected plants (cv. Lindou No.10) were growing poorly and the roots showed distinct brown lesions (Fig. S2). Pratylenchus spp. were extracted using the modified Baermann funnel method for 2 days (Hooper et al. 2005). On average, 395 root-lesion nematodes per kg of soil and 36 root-lesion nematodes per gram of fresh roots were extracted. The extracted root-lesion nematodes were disinfected with 0.3% streptomycin sulfate and cultured on carrot disks for propagation at 25°C. The species identification was based on morphological and molecular criteria. Key morphological features were determined for females and males. Measurements of females (n = 16) included body length = 561.0 μm ± 37.6 (standard deviation) (520.5 to 654.0 μm), tail length = 30.0 μm ± 1.9 (27.0 to 33.5 μm), stylet = 16.0 μm ± 0.6 (15.0 to 17.5 μm), a = 28.2 ± 2.3 (23.7 to 31.5), b = 6.4 ± 0.5 (5.7 to 7.3), c = 18.7 ± 1.8 (15.7 to 23.8), and V = 80.8% ± 2.1 (76.5 to 83.8%). Measurements of males (n = 16): body length = 511.0 μm ± 28.1 (range= 475.5 to 566.0 μm), tail length = 26.0 μm ± 1.3 (23.5 to 28.5 μm), stylet = 15.0 μm ± 0.5 (14.5 to 16.0 μm), spicule length = 17.0 μm ± 0.9 (16.0 to 18.5 μm), a = 30.8 ± 1.5 (28.0 to 33.2), b = 6.1 ±0.4 (5.6 to 6.9), and c = 19.8 ± 1.3 (18.1 to 22.2) (Fig. S3). All the morphological features of this population matched the description of P. coffeae (Castillo and Vovlas, 2007). DNA was extracted from an individual female as described previously (Wang et al. 2011). The rDNA-internal transcribed spacer (ITS) region and the D2/D3 region of the 28S rRNA gene were amplified by primers 18S/26S (Vrain et al. 1992) and D2A/D3B (De Ley et al. 1999), respectively. The PCR products were purified and sequenced. The obtained sequences of the ITS region (1,253 bp) and the D2/D3 region of 28S rRNA (781 bp) were deposited in GenBank. The ITS sequences of the root-lesion nematode obtained in this study (GenBank Accession no. MT879294) exhibited 99% identity with several P. coffeae sequences available in the GenBank (e.g., KR106219, MT586756, KY424205, and MN749379), and the obtained D2/D3 region sequence (MT879295) exhibited 100% identity with several P. coffeae sequences (e.g., MT586754, MN750755, MK829009, and MH730447). Both morphological and molecular data confirmed the presence of P. coffeae. To confirm reproduction on soybean, the obtained root-lesion nematode population was used in a greenhouse (25°C) assay to fulfill modified Koch's postulates. About 20 days after sowing, eight pots, each with one soybean plant (Lindou No.10) were inoculated with 1000 P. coffeae. The inoculated plants were kept in 1.5 L pots containing 1.2 L sterilized soil. Eight pots of uninoculated soybeans were used as the control. Ten weeks later, the inoculated roots were washed and brown lesions were observed. The number of nematodes/pot was approximately 7360 in soil and 796 in roots, and the reproduction factor was 8.16. Root-lesion nematodes and symptoms were not observed in control groups. P. coffeae has only been reported on soybean in Zhejiang (Wei et al. 2013) and Henan Province (Li et al. 2019) of China. To our knowledge, this is the first report of P. coffeae infecting soybean in Shandong Province, China. Since the root-lesion nematode can cause considerable damage to soybean, care should be taken to prevent the spread of P. coffeae to other regions in China.

Polyethylene and biodegradable plastic mulches improve growth, yield, and weed management in floricane red raspberry

Polyethylene (PE) mulch and biodegradable plastic mulches (BDMs) have been used in annual vegetable and strawberry (Fragaria × ananassa Duch.) production systems for several decades due to their ability to suppress weeds, modify soil temperature and moisture, and promote earlier and greater yields. However, there are only a few studies that have explored mulch use in perennial production systems. The overall objective of this study was to compare PE mulch and BDMs to growers’ standard practice of bare ground (BG) cultivation in a floricane red raspberry (Rubus idaeus L.) production system in northwestern Washington, USA. Cumulative weed growth, root lesion nematode [Pratylenchus penetrans (Cobb) Filipjev and Schuurmans Stekhoven; RLN] population densities, soil temperature and moisture, cumulative plant growth, and fruit yield were evaluated in a ‘Wake™Field’ red raspberry field in 2017 and 2018. Compared to the BG control, PE mulch and BDMs suppressed weeds and generally increased soil temperature. Root lesion nematode population densities were greater in soil covered with PE mulch than Novamont 0.5, and were greater in raspberry roots from plots treated with PE mulch than BASF 0.6 and the BG control. Primocane height and number were higher for plants grown with mulches relative to the BG control in 2017. Average fruit yield of plants from the mulched treatments was 34% greater than the BG control. Overall, this research demonstrated that PE mulch and BDMs improved raspberry plant growth and yield. These findings demonstrate the potential benefits of using PE mulch and BDMs for improving establishment in perennial crops.

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 vulnus associated with apple in Tunisia.

Abstract The root-lesion nematode of the genus Pratylenchus Filipjev (1936) has a worldwide distribution and cause severe production constraints on numerous important crops. In 2013-14, during a survey of the apple nurseries and orchards in center of Tunisia (Kairouan, Zaghouan, Monastir and Kasserine), 70 different roots and soil samples were collected. The populations of root-lesion nematode were identified on the basis of their morphological and morphometric characters, and by molecular methods. Microscopic observation of females and males demonstrated the occurrence of Pratylenchusd vulnus on apple trees. The ribosomal DNA D2-D3 expansion segments of the 28S rRNA and of the Pratylenchus populations were PCR amplified and sequenced. The sequences were compared with those of Pratylenchus species in the GenBank database with high similarity (99%). This comparison reconfirmed the morphological identifications. Phylogenetic studies placed those populations with P. vulnus. This is the first report of P. vulnus infecting apple in Tunisia.

Elevated temperature reduces survival of peak populations of root-lesion nematodes (Pratylenchus thornei) after wheat growth in a vertisol

Elevated temperature was investigated to understand why there is a faster decline in Pratylenchus thornei population abundances in the topsoil than in deeper layers of vertisols after wheat matures in the subtropical grain region of eastern Australia. Soil containing a large population abundance of P. thornei (after wheat growth) was incubated in a replicated experiment for various periods up to 16 weeks at eight temperatures ranging from 10 to 45 °C in 5 °C intervals, with three moisture treatments, namely (a) field capacity maintained during incubation, (b) field capacity allowed to dry during incubation and (c) air-dried before incubation. After incubation, live nematodes were extracted from the soil samples by the Whitehead tray method for 2 and 7 days and P. thornei was counted in four life-stage categories. Temperatures ≥ 35 °C resulted in rapid death of P. thornei independent of any effects due to soil desiccation. At lower temperatures, survival over a 16-week period was better in soil maintained at field capacity than in soil allowed to dry. Death of P. thornei in soil that was air-dried before incubation was rapid during incubation at all temperatures tested. Elevated temperature of itself plus faster soil desiccation with increasing temperature are the likely causes of the faster decline in P. thornei population abundances in the topsoil than in the subsoil. These effects can contribute to soil profile distributions of P. thornei recorded in some fields in this subtropical grain region after clean fallow periods where greater population abundances of P. thornei occur in the subsoil layers than in the topsoil.

Compost and poultry manure as preplant soil amendments for red raspberry: Comparative effects on root lesion nematodes, soil quality and risk of nitrate leaching

Raspberry fields in the Pacific Northwest, USA and British Columbia, Canada are often prepared for replanting by fumigating with broad-spectrum biocides to control root-lesion nematodes, Pratylenchus penetrans. Nematode-suppressive organic amendments have been advocated as reduced risk alternatives to fumigation but may pose other risks to the environment. This study compared alternative pre-plant soil management practices with respect to their effects on plant-parasitic nematode populations, soil quality parameters and risk of nitrate leaching. In fall of 2009 and 2010, a mature raspberry field was mowed down and plowed, and replicate plots were randomly allocated to each of six treatments: (1) a non-amended control, (2) fumigation with Basamid®, (3) fall seeded barley cover crop, (4) recommended rate (20m3ha−1) and (5) historical “biofumigant” high rate (250m3ha−1) of spring incorporated poultry manure, and (6) spring incorporated compost (250m3ha−1). Raspberry cv Saanich was planted approximately one month after incorporation of amendments. Composite soil samples were taken from each plot at multiple times during two subsequent growing seasons and analyzed for nematode populations and soil chemical and physical properties. Primocane biomass was assessed at the end of each of the first two growing seasons as an index of crop vigor. The high poultry manure and compost treatments suppressed root-lesion nematode populations nearly as well as fumigation over two growing seasons. These treatments also improved soil bulk densities and aggregation relative to control, cover crop and fumigation treatments, while compost addition beneficially increased soil pH, CEC and Ca concentrations more than manure. Primocane production in the manure and compost treatments was greater than in the control and cover crop treatments, but less than in the fumigated treatment. Substantial nitrate accumulation in soil amended with the high rate of manure indicated that application of sufficient manure to suppress parasitic nematodes would pose a significant risk of nitrate leaching. In contrast, soil nitrate accumulation was not significantly increased in the compost amended plots. Overall, compost application reduced nematode populations, improved crop growth and did not increase the risk of nitrate leaching in the short term and may be a viable alternative to fumigation.

Characterisation of amphimictic and parthenogenetic populations of Pratylenchus bolivianus Corbett, 1983 (Nematoda: Pratylenchidae) and their phylogenetic relationships with closely related species

Amphimictic populations of root-lesion nematodes with numerous males and females having three lip annuli, a functional spermatheca and non-areolated lateral field occur on sword fern (Nephrolepis exaltata) in Florida. Identified for decades asPratylenchus penetrans, they appeared to be a morphologically separated species on the basis of a longer stylet (17.8-18.3 μm) thanP. penetrans(15-17 μm) and different lip pattern inen faceview (rectangularvsdumb-bell inP. penetrans). Morphologically similar amphimictic root-lesion nematodes have also been detected on flax lily in Costa Rica. Subsequent morphological observations indicated that these amphimictic root-lesion nematodes from fern and flax lily are closely related to the parthenogenetic speciesP. bolivianus, which has areolated lateral fields. In spite of the reproductive and morphological dissimilarities between these populations, their separation into different species was not supported by the results of molecular analyses of their DNA sequences. The populations used in these analyses included those that are amphimictic from Florida and Costa Rica and others that are parthenogenetic from the type locality in Bolivia, and geographically distant localities in Chile, China, Colombia and Europe. Phylogenetic analyses of the ITS and D2-D3 expansion segments of the 28S rRNA gene indicated that they belong to the same species,P. bolivianus, which consists of two morphotypes,P. bolivianus(am) amphimictic andP. bolivianus(pm) parthenogenetic, herein described and illustrated. Contradictory results were obtained by the analyses using a portion of thehsp90gene. The phylogenetic study, which included sequences of other root-lesion nematodes, a topotype and geographical distant populations ofP. zeae, revealed thatP. bolivianusandP. zeaeformed highly supported clades in the majority consensus trees. PCR with species-specific primers for rapid diagnostics ofP. bolivianusandP. zeaewere developed and tested.

Diversity of root-lesion nematodes (Pratylenchus spp.) associated with wheat (Triticum aestivum and T. durum) in Morocco

Root-lesion nematodes (Pratylenchus) have a worldwide distribution and cause severe production constraints on numerous important crops. During a survey of the wheat-growing area of Morocco, 17 populations of root-lesion nematode were collected. They were identified on the basis of their morphological and morphometric characters, and by molecular methods. Microscopic observations of females and males demonstrated the occurrence ofP. penetransin 13 of the 17 samples;P. thorneiandP. pseudocoffeaewere detected in four samples from Zaers and a single sample from Settat, respectively. A duplex PCR primer set was used to confirm the presence ofP. penetranswhile the species-specific forward primer PTHO and the common reverse primer D3B were used forP. thornei. For the remaining populations, the D2-D3 expansion segments of the 28S rRNA gene were amplified and the obtained sequences were compared with those ofPratylenchusspecies in the GenBank database. This comparison confirmed the morphological identifications and revealed a population ofP. pinguicaudatus. The study of the phylogenetic relationship of the MoroccanPratylenchuspopulations showed a high similarity (99-100%) between allP. penetranspopulations. The population dynamics of sixPratylenchuspopulations from Morocco were evaluated on carrot disk cultures at 4, 8 and 12 weeks after inoculation, and at 10, 15, 20 and 25°C. The optimum temperature for reproduction of all populations was 20°C. After 8 weeks at this temperature, nematode numbers increased up to 458-fold, 310-fold and 252-fold for the four populations ofP. penetrans, theP. thorneiand theP. pseudocoffeaepopulation, respectively.

Relationship among soil properties, root-lesion nematode population, and soybean growth

Root-lesion nematode (RLN) (Pratylenchus brachyurus) is an important challenge to soybean production in Central Brazil due to its widespread occurrence, along with the absence of resistant cultivars and strategies for its management. The aim of this research was to evaluate the relationship among soil properties, RLN populations, and soybean crop growth using geostatistical analysis. The experiment was conducted in a soybean field located in the northern half of Mato Grosso state, in Brazil, with a history of damages by RLN. The results suggest a positive correlation between plant height and values of pH, Ca, Mg, and base saturation. On the other hand, RLN population was positively correlated with organic carbon, cation exchange capacity, and soil potential acidity. Moreover, our findings also indicate that soybean plant growth is reduced under acidic soil conditions, as susceptibility to RLN increases. Thus, the correction of soil acidity to suitable levels for soybean crop becomes an important strategy to minimize damages by RLN.

Composted Dairy Manure and Alfalfa Hay Mulch Affect Soil Ecology and Early Production of ‘Braeburn’ Apple on M.9 Rootstock

A variety of organic mulches and amendments have been observed to improve soil quality and productivity of apple orchards. Alfalfa hay and composted dairy manure solids (CDS) are readily available in the apple-growing region of the Pacific Northwest and British Columbia and could be used to improve orchard performance. The objective of this research was to determine the influences of CDS amendment and alfalfa hay mulch on populations of soil microfauna, soil chemical properties, and early growth; nutrient uptake; and yield of apple planted into a fumigated coarse-textured soil in central Washington State. Alfalfa mulch significantly improved tree vigor and fruit yield with minimal adverse effects on fruit quality, whereas the CDS amendment had minor effects on vigor and yield. Both alfalfa mulch and CDS amendment increased availability and uptake into leaves and fruit of most key nutrients but plant nutrient concentrations were not deficient in control plots, suggesting that increased nutrient availability was probably not the primary reason for the increased vigor attributed to alfalfa mulch at this site. The alfalfa mulch resulted in elevated populations of microbivorous nematodes and protozoa that persisted through later years of the experiment, indicating greater overall microbial activity, mineralization of nutrients, and possible direct stimulation of root growth under mulch; the CDS amendment did not consistently enhance populations of microbivorous nematodes. The alfalfa mulch, but not CDS amendment, suppressed the buildup of populations of root-lesion nematodes, which are important components of the replant disease complex that was suppressing tree growth at the site despite the preplant fumigation. Accordingly, we speculate that the reduced impacts of root-lesion nematodes contributed to the improved vigor and fruit yield of trees grown with alfalfa hay mulch.

Root-lesion nematode (Pratylenchus thornei) reduces nutrient response, biomass and yield of wheat in sorghum–fallow–wheat cropping systems in a subtropical environment

Wheat in winter and grain sorghum in summer are the most important crops of the subtropical grain region of eastern Australia, where they are often grown in sequences of 1–4 years of each crop species separated by a long fallow period of 11–14 months. Growers have observed that the second wheat crop in sequence can appear nutrient deficient with poor growth and grain yield compared with the first or subsequent crops. To investigate this problem, wheat was grown in various field experiments as the first–fourth wheat in sequence after long fallow from sorghum sequences of various lengths (one–four years) to test for responses in biomass production and grain yield to fertilisers, biocidal fumigants and nematicides. Populations of root-lesion nematodes (Pratylenchus thornei) were greatest in the soil before the second wheat crop was sown than before the first or third wheat crops. Greatest responses in wheat growth were obtained to the nematicide aldicarb in various wheat sequence positions up to the fourth (up to 137% increased yield of second wheat). Aldicarb best protected the roots from P. thornei allowing increased nutrient response. The fumigants chloropicrin and dazomet caused substantial changes in soil microbial populations and available nutrients, but the systemic nematicides fenamiphos and aldicarb did not. Responses in grain yield were also obtained to N fertiliser and less frequently to P and Zn (41% increase of second wheat to NPZn fertiliser), with best overall responses to a combination of aldicarb and fertiliser. A range of tolerance to P. thornei, as judged by both grain yield from nil treatment and response to aldicarb and/or fertiliser, was identified among wheat cultivars. In comparison, one barley cultivar yielded maximally without treatment (up to 3.7 and 1.3 times the yield of the most intolerant and the most tolerant wheat cultivars, respectively). Integrated management using crop rotation with sorghum to reduce P. thornei populations combined with growing tolerant wheat and barley cultivars supplied with adequate fertiliser are practical measures to reduce the impact of P. thornei.

Erratum to: Suppressive biological factors influence populations of root lesion nematode (Pratylenchus thornei) on wheat in vertosols from the northern grain-growing region of Australia

Soils from the grain-growing region of northern Australia were assessed for suppressiveness to Pratylenchus thornei by comparing nematode multiplication rates on wheat grown in sterilised soil, non-sterilised soil and sterilised soil to which 10% field soil had been added; or by looking for soils in which the nematode failed to multiply under conditions that favoured nematode multiplication. Bioassays with cropped soils indicated that multiplication of P. thornei consistently increased when soil was sterilised by heat or irradiation, with final population densities in sterilised soil typically 22–35 nematodes/g soil compared with only 2–8 nematodes/g in untreated soil. Soils from native vegetation and pasture reacted in much the same way. Results of other bioassays indicated that multiplication of P. thornei was sometimes reduced by transferring field soil to sterilised soil, and that the nematode failed to multiply in soil from some farms, particularly if that soil was collected from the upper 25 cm of the soil profile. These results suggest that biological mechanisms of suppression are operating in many of these soils. However, shoot growth generally improved when soil was sterilised and so it is also possible that increased root biomass or better root health was partly responsible for differences in nematode multiplication rates between sterilised and non-sterilised soil. Alternative ways of assessing suppressiveness and furthering our understanding of the factors that influence population densities of P. thornei are discussed.

Suppressive biological factors influence populations of root lesion nematode (Pratylenchus thornei) on wheat in vertosols from the northern grain-growing region of Australia

Suppressive biological factors influence populations of root lesion nematode (Pratylenchus thornei) on wheat in vertosols from the northern grain-growing region of Australia

A new species of the genus Pratylenchus from chrysanthemum in Kyushu, western Japan (Nematoda: Pratylenchidae)

A root-lesion nematode population collected from rhizospheres of Chrysanthemum morifolium in Kyushu Is., western Japan, is described as Pratylenchus kumamotoensis sp. n. The new species is characterized by its esophageal glandular lobe (EGL) inconsistently overlapping the intestine (dorsal, lateral and ventral overlap in varied frequencies), 2-3- annules in lip region, average spear length 14-15 μm, moderately distanced vulva (V = 76- 77), and thin tail terminal cuticle (< 2 μm). The new species is distinguished from closely related P. coffeae, P. pseudocoffeae, P. loosi, P. jaehni, and Apratylenchoides homoglans. The new species was placed in the genus Pratylenchus because of the lack of clear differences with the genus Pratylenchus. However, an inconsistent overlap of the EGL in the new species creates grave doubt about the separation of Pratylenchus and Apratylenchoides.

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.

Effects of aldicarb and fungicides on Pratylenchus penetrans populations, root rot and net blotch severity on barley

Population levels of the root lesion nematode, Pratylenchus penetrans, which produces necrotic lesions in the root cortex, were recorded in barley (Hordeum vulgare) in experimental plots during 1988, 1989, and 1990. Root lesion nematodes were the onlyendoparasitic nematodes recovered from barley roots and were the dominant nematode group found in the soil. Based on 3-yr averages, root rot ratings, caused primarily by Cochliobolussativusand Fusarium spp., increased from 27% at Zadoks Growth Stage (ZGS) 30-32 in July to 73 % at ZGS 70-72 in late August and early September. Net blotch (incited by Pyrenophora teres) was suppressed by a fungicide treatment consisting of a seed application of carbathiin and thiram, and a foliar application of propiconazole. Aldicarb suppressed the populations of root lesion nematodes in the soil, in the total root System, and in crown and seminal roots of barley. Yields were increased by ca 30% where aldicarb and fungicides were applied as a combined treatment. Population densities of root lesion nematodes were much greater in seminal roots than in crown roots at ZGS 30-32 and 55-60. Correlation coefficients between nematodes and yield data were often negative and significant (P≤0.05). There were no consistent trends in the numerical relationships between numbers of root lesion nematodes in roots or soil, and incidences of net blotch or root rot of barley.