Plant-parasitic Nematode Species Research Articles

Comprehensive Phylogenetic Analysis of Root-knot Nematodes Predicts Emerging Virulent Species

Among the root-knot nematodes three <i>Meloidogyne</i> species namely <i>Meloidogyne incognita, M. javanica</i>, and <i>M. arenaria</i> are emerging as an important pest of many cultivated plants, and recognized as the most economically destructive plant parasitic nematodes species of all over the world. Although other root-knot nematodes may virulent for plant but limited information is available. Thus, a comprehensive bioinformatics analysis including sequence acquisition, multiple sequence alignment and the phylogenetic tree construction for well-known <i>Meloidogyne</i> species was employed to predict the emerging virulent species. About eighty seven (87) 18S rRNA sequences of three damaging <i>Meloidogyne</i> species (<i>M. javanica, M. arenaria</i> and <i>M. incognita</i>) were retrieved from NCBI database, and allowed to construct phylogenetic trees using both NJ and ME methods of Molecular Evolution Genetic Analysis (MEGA) tools. Phylogeny analysis revealed that <i>M. enterolobii_1, M. sp._Mi_c3a, M. sp_Mj_c1a</i> and <i>M._sp._Mj_c3a</i> are genetically as well as evolutionally related to existing well recognized virulent nematodes. Moreover, evolutionally emerging strains of existing virulent species of <i>M. javanica, M. arenaria</i> and <i>M. incognita</i> along with the predicted virulence nematodes could become a great challenge to agriculture. The study could initiate the further analysis for novel insights in the pathogenesis of emerging virulence species of <i>Meloidogyne</i> that must be needed for future crop management strategies.

Plant-parasitic nematodes associated with the root zone of hop cultivars planted in a Florida field soil.

In early 2016, hop plants were introduced into Florida. By late 2016, the hop plants were showing stunted growth and were heavily parasitized by Meloidogyne javanica. In this study, we determined host susceptibility of 14 hop cultivars to M. javanica in a greenhouse experiment and monitored population development of plant-parasitic nematode species in the root zone of 17 hop cultivars planted in three newly established hop yards in Florida. Plant-parasitic nematodes in the rooting zone soil of field grown hop plants included M. javanica, Pratylenchus brachyurus, Paratrichodorus minor, Belonolaimus longicaudatus, Xiphinema setariae/vulgare complex, Mesocriconema xenoplax, and Helicotylenchus dihystera; however, soil population densities of P. minor, B. longicaudatus, X. setariae/vulgare complex, M. xenoplax, and H. dihystera remained low through the study. Root galling, M. javanica egg production, and soil population densities of M. javanica were consistently large on the ‘Canadian Red Vine’, ‘Centennial’, ‘Chinook’, and ‘Comet’ cultivars, and small on the ‘Galena’ and ‘Triple Perle’ cultivars. No differences were observed in soil population densities of P. brachyurus among hop cultivars. Overall, our study provides the first report of plant-parasitic nematode population development in the root zone on hop cultivars planted in Florida.

IMPACT OF PLANT GROWTH PROMOTING RHIZOBACTERIA AS BIO-CONTROL AGENTS ON CITRUS NEMATODE, TYLENCHULUS SEMIPENETRANS INFECTING BALADY ORANGE (CITRUS SINENSIS L.) AND IMPROVING ITS PRODUCTIVITY

Three bacterial species of plant growth promoting rhizobacteria (PGPR) namely Paenibacillus polymyxa, Methylobacterium mesophilicum and Methylobacterium radiotolerans were tested alone or combined with humic acid as bio-control agents against the citrus nematode Tylenchulus semipenetrans under laboratory and field conditions. Results cleared that; all tested PGPR species produced IAA, HCN, ammonia, chitinase and protease enzymes and also solubilized phosphate in laboratory. P. polymyxa emphasized the superiority among other species in all PGPR properties except for phosphate solubilization, whereas M. radiotolerans showed highest amount of phosphorus solubilized in culture media. On the other hand, the results of the nematode survey conducted on orange, Citrus sinensis L. cv Balady grown in different localities of Ismailia and Sharkia Governorates during season 2019, revealed the presence of seven genera and species of plant-parasitic nematodes. Among which, T. semipenetrans occurred in all examined samples (100% frequency of occurrence) with a relatively high population density of 2330 and 2640 infected juveniles (J2) /250 g soil in Ismailia and Sharkia Governorates, respectively. Field experiments were conducted in two different locations, at Ismailia and Sharkia Governorates to assess the effectiveness of PGPR strains alone or combined to reduce the numbers of T. semipenetrans during season 2019. It was found that, all treatments caused significant (P≤0.05) reduction in T. semipenetrans population, compared to control treatment. The nematicide, Nemathorin® 10% G followed by P. polymyxa (20 L.fed-1 ) + foliarspraying of M. mesophilicm (5 L.fed-1 ) gave the highest efficacy in controlling the citrus nematode. Percentage reduction in numbers of J2/250g soil and adult females/1g roots for these treatments in Ismailia Governorate were 91% (85.7%) and 91.4% (89.5%), respectively. While the parallel values in Sharkia Governorate were 90% (87%) and 94% (90%), respectively. The combination of P. polymyxa and humic acid (20 L.fed-1 ) with foliar spraying of M. mesophilicm (5 L.fed-1 ) gained the third position. All treatments increased the fruit yield compared to control treatment. The highest percentages of increase were determined with Nemathorin (160% and 206%) followed by P. polymyxa + Humic acid (20 L.fed-1 ) + foliar spraying of M. mesophilicum (155.7% and 193%) and M. radiotolerans + P. polymyxa + foliar spraying of M. mesophilicum (153% and182%) in Ismailia, and Sharkia Governorates respectively.

Candidate genes underlying the quantitative trait loci for root-knot nematode resistance in a Cucumis hystrix introgression line of cucumber based on population sequencing

The southern root-knot nematode (RKN), Meloidogyne incognita (Kofoid & White) Chitwood, is one of most destructive species of plant parasitic nematodes, causing significant economic losses to numerous crops including cucumber (Cucumis sativus L. 2n = 14). No commercial cultivar is currently available with resistance to RKN, severely hindering the genetic improvement of RKN resistance in cucumber. An introgression line, IL10-1, derived from the interspecific hybridization between the wild species Cucumis hystrix Chakr. (2n = 24, HH) and cucumber, was identified with resistance to RKN. In this study, an ultrahigh-density genetic linkage bin-map, composed of high-quality single-nucleotide polymorphisms (SNPs), was constructed based on low-coverage sequences of the F2:6 recombinant inbred lines derived from the cross between inbred line IL10-1 and cultivar ‘Beijingjietou’ CC3 (hereinafter referred to as CC3). Three QTLs were identified accounting for 13.36% (qRKN1-1), 9.07% and 9.58% (qRKN5-1 and qRKN5-2) of the resistance variation, respectively. Finally, four genes with nonsynonymous SNPs from chromosome 5 were speculated to be the candidate RKN-resistant related genes, with annotation involved in disease resistance. Though several gaps still exist on the bin-map, our results could potentially be used in breeding programs and establish an understanding of the associated mechanisms underlying RKN resistance in cucumber.

Antagonistic role of the microbiome from a Meloidogyne hapla-suppressive soil against species of plant-parasitic nematodes with different life strategies

Summary In certain soils populations of plant-parasitic nematodes (PPN) decline. Understanding this effect may open up environmentally friendly management options. We identified such a suppressive soil containing virtually no PPN. Inoculated Meloidogyne hapla declined in this soil more than in a control soil and reproduction on tomato was reduced. The extracted soil microbiome alone decreased root invasion of second-stage juveniles (J2) and progeny as well as the native soil. We tested the antagonistic potential against PPN that differ in life strategies. The microbiome was most suppressive against two populations of M. hapla and one population of Pratylenchus neglectus, and least suppressive against M. incognita and the ectoparasite Hemicycliophora conida. In a split-root system with M. hapla, plant-mediated but not direct effects of the microbiome significantly reduced root invasion of J2, while direct exposure of M. hapla to the microbiome significantly affected reproduction. Overall, both plant-mediated and direct effects of the microbiome were responsible for the soil suppressiveness against M. hapla.

How Low Can They Go? Plant-Parasitic Nematode Distribution in a Washington Vineyard

Summary Goals: To map the distribution of two plant-parasitic nematode species, the northern root-knot nematode Meloidogyne hapla and the dagger nematode Xiphinema spp., in a Washington State winegrape vineyard slated for replanting. These nematode species can reduce vineyard longevity and weaken or kill young vines. Knowing how these nematodes are spatially distributed in soil can improve implementation of management strategies. Key Findings: Northern root-knot nematode and dagger nematode had distinctly different distributions within the soil profile. Northern root-knot nematode was concentrated near the vine rows and drip-irrigation lines, in the upper 61 cm (24 inches) of the soil profile. This is reflective of its life strategy, in which association with fine roots and areas of moisture is essential. Dagger nematode was relatively evenly distributed at all distances from the vine row, and significant populations were found down to the deepest sampling depth of 122 cm (48 inches). This demonstrates that it can survive readily on hosts other than grape and can parasitize root types that are not parasitized by northern root-knot nematode. Impact and Significance: This work provides evidence for how and why nematode management practices may differ in their efficacy. Dagger nematodes were distributed throughout the sampled area and were found at depths that most fumigation efforts cannot reach. This increases the likelihood that dagger nematodes will recolonize treated areas, but this may take time as they move upward from deep in the soil. Root-knot nematodes may be more easily controlled via chemigation or fumigation, as their distribution corresponds to shallower areas with high fine root biomass wetted by drip irrigation.

Three new species of the spiral nematode genus helicotylenchus steiner, 1945 (nematoda: hoplolaimidae) from Vietnam

Investigations on entomopathogenic and plant parasitic nematodes in some natural forests in the Ngoc Linh mountain (Quang Nam province) and the Thuong Xuan forest (Thanh Hoa province) revealed three new species of plant parasitic nematodes belonging to the genus Helicotylenchus Steiner, 1945 (Nematoda: Hoplolaimidae). These new species were named Helicotylenchus castanus sp. n., Helicotylenchus madhucus sp. n. and Helicotylenchus digitus sp. n. with morphological characteristics described and illustrated. The new species Helicotylenchus castanus sp.n. is characterized by the highly hemispherical shape of the lip region, extremely short and rounded tail without projection. The second new species Helicotylenchus madhucus sp. n. is characterized by high lip region with 4-5 annuli, hemispherical and not set off from body contour, stylet 31.3-35.9 (33.3 ± 1.3) µm long, tail with a short ventral projection and the presence of males in the population. The third new species, Helicotylenchus digitus sp.n. was recognized by broad rounded tail with strong annulated projection in the digital shape, and also the presence of males in population.

Identification of plant-parasitic nematodes associated with cut flowers

Carnation, gerbera and lisianthus are an important part of the cut flower market worldwide, but plant-parasitic nematodes (PPN) affect their production and quality. Therefore, rapid and accurate identification of PPNs is required for effective pest management programmes and crop rotation. In this study, a survey was carried out in the Antalya province of Turkey, an area where carnation, gerbera, lisianthus and chrysanthemum are commercially grown. A total of 79 soil samples were collected from greenhouses in the area, and 12 species-specific primers for identification of Meloidogyne, Pratylenchus and Rotylenchulus species were used for molecular detection. Pratylenchus thornei, M. incognita, P. neglectus, M. javanica, M. arenaria and M. hapla were detected in 98.73%, 88.60%, 65.82%, 34.17%, 22.78% and 5.06% of samples, respectively. Results showed combination of different PPN species in the soil of greenhouses where cut flowers were grown. These findings may be used to improve management practices, reducing losses in cut flower production.

Integrated management of plant-parasitic nematodes on guava and fig trees under tropical field conditions

Two field experiments were carried out to study the efficacy of different biological control agents in controlling certain plant-parasitic nematode species including Meloidogyne javanica, Tylenchorhynchus mediterraneus, Hoplolaimus seinhorsti, Longidorus latocephalus, and Xiphinema elongatum on guava and fig trees under the tropical field conditions of Jazan region, south-west Saudi Arabia during two successive seasons from Feb. 15, 2016 to Jan. 15, 2017. The evaluated bio-agents were used in different integrated management combinations of certain fungal species (Trichoderma harzianum, Verticillium chlamydosporium, and Purpureocillium lilacinum), the bacterium Pasteuria penetrans, some organic amendments (cow manure, compost, and chicken manure), urea 46% as a nitrogenous fertilizer, and the nematicide carbofuran 10G for comparison. Results showed that all the tested treatments gradually decreased (P ≤ 0.05) the population densities of plant-parasitic nematodes on guava and fig trees over the study period. The highest reduction of nematode densities occurred at the end of the experiment. Carbofuran 10G was the most effective treatment in suppressing the nematode densities on guava and fig trees. The most effective management combinations, next to carbofuran 10G, in suppressing the nematode densities in the rhizosphere of guava trees were P. lilacinum + P. penetrans + urea 46%, P. lilacinum + P. penetrans + chicken manure, and T. harzianum + P. penetrans + chicken manure (66.54–69.22% nematode reductions). Correspondent combinations in the rhizosphere of fig trees were P. lilacinum + P. penetrans + cow manure, T. harzianum + P. penetrans + cow manure, P. lilacinum + P. penetrans + urea 46%, and V. chlamydosporium + P. penetrans + urea 46% (54.68–57.17% nematode reductions). On the other hand, nematode population densities continued to increase (P ≤ 0.05) in the rhizosphere of guava and fig trees in the absence of nematode management combinations. All the tested treatments significantly increased (P ≤ 0.05) the number of fruits/tree on guava and fig trees. Treatments which included the combinations of fungal and bacterial parasites along with chicken manure gave the highest numbers of fruits/tree, followed by the treatment with the nematicide carbofuran 10G. Regression analysis showed a significant negative linear relationship between the number of nematodes/kg soil and the number of guava and fig fruits/tree.

First record of three plant parasitic nematode species from Mount Ararat (Ağrı) in Turkey

In this study, plant parasitic nematode fauna from Mount Ararat was determined according to altitude. A total of 30 soil samples were taken in 2013 during summer. Nematodes were extracted by a modified Baermann funnel technique. Nematodes were identified by morphology, morphometric and phylogenetic analysis based on sequences of the D2-D3 and ITS1-rRNA gene sequences. Permanent slides of individuals were made and species-specific characters were screened by scanning electron microscopy (SEM). SEM studies were processed at the Department of Animal Biology, Vegetal Biology and Ecology, SEM laboratory University of Jaén in Spain during 2014. A total of 19 plant parasitic nematodes were identified from Mount Ararat. Three plant parasitic nematodes Rotylenchus conicaudatus Atighi et al., 2011 (Nematoda: Hoplolaimidae), Heterodera trifolii Goffart, 1932 (Nematoda: Heteroderidae) and Tylenchorhynchus mangiferae (Nematoda: Belonolaimidae) from this study are new records for plant parasitic nematode fauna of the Turkish.

In vitro nematicidal activity of natural and semisynthetic cadinenes from Heterotheca inuloides against the plant-parasitic nematode Nacobbus aberrans (Tylenchida: Pratylenchidae).

Nacobbus aberrans (Tylenchida: Pratylenchidae) is one of the main plant-parasitic nematodes species that affects crops in Mexico, generating substantial economic losses. Traditionally, the control of the nematodes is carried out using chemical products; however, research efforts are presently focused on the search for new methods for the control of this pest. Natural products derived from plants are an alternative for the control of populations of plant-parasitic nematodes. The genus Heterotheca (Asteraceae) is characterized by containing sesquiterpenes with cadinane skeleton, and some species of this genus exert nematicidal activity. We determined the effects of selected Heterotheca inuloides plant metabolites and some semisynthetic derivatives on the hatching of eggs isolated from the gelatinous matrix and infective second-stage juveniles (J2) of the false root-knot nematode N. aberrans using an in vitro experimental model. Among the evaluated compounds, nematodes were more susceptible to hydroxylated and quinone compounds, whereas the remaining compounds showed moderate or no activity. The presence of the hydroxyl group is essential for nematicidal potential, with changes at the hydroxyl group modifying the nematicidal activity. Flowers of Heterotheca inuloides contain bioactive compounds that showed nematicidal activity against N. aberrans. Here we report the nematicidal activities of cadinenes isolated from the flowers of H. inuloides and their semisynthetic derivatives against the false root-knot nematode N. aberrans. © 2018 Society of Chemical Industry.

Major sperm protein BxMSP10 is required for reproduction and egg hatching in Bursaphelenchus xylophilus

The pine wood nematode Bursaphelenchus xylophilus is a disastrous pathogen of pine forests in East Asia and Europe. Despite its decimating effect on pine forests, efficient and environmentally friendly methods available to control the pine wood nematode (PWN) are limited. The most abundant protein in nematode sperm, major sperm proteins (MSPs) have only been discovered in nematodes. In this study, phylogenetic analysis showed that BxMSP10 was highly conserved in the nematode and had a closer phylogenetic relationship with free-living nematodes than with plant-parasitic nematode species. BxMSP10 was specifically expressed in the seminal vesicle of male adults. dsRNA of BxMSP10 significantly decreased reproduction, egg hatching and population maintenance in B. xylophilus. These results indicated that BxMSP10 was a potential candidate for application in the control of B. xylophilus.

Embryogenesis, penetration and post penetration development of Meloidogyne enterolobii in Guava (Psidium guajava L.)

Guava (Psidium guajava L.) is one of the important commercial fruit crops grown in India. A new species of rootknot nematode Meloidogyne enterolobii reported first from India by Poornima et al., 2016, has become a fast spreading problem in guava cultivation causing severe reduction in yield and decline of guava orchards across the country and world. The present study was taken up to observe the activity of developmental stages such as embryonic, penetration and post penetration stages of M. enterolobii in order to get a clear picture of the vulnerable stage for managing the nematode. It was observed that the average size of a viable egg was 42.48 μm (±4.20 μm) in length and 20.21 μm (±1.70 μm) in width (n = 10). The average number of eggs/egg masses was 179 (±16) (n = 10). These dimensions are comparable to the dimensions described for eggs of many other plant parasitic nematode species. The 3rd stage juveniles were observed in 2–3 days after Jstage and Jstages were observed in 4–5 days after J3 stage. The swollen female or immature stage of females were seen at 2–3 days after J4 stage, fully developed female was observed in guava roots at 24–28 days starting with single cell stage, the female starts laying eggs at 28–30 days from single cell stage. The optimal temperature for development of M. enterolobii is 28°C, and corresponds to the geographical distribution of this nematode in subtropical regions. At this temperature it takes approximately 3 weeks to complete one life cycle.

Nematicidal activity of fipronil against Pratylenchus zeae in sugarcane

Abstract No nematicide has been registered for controlling plant-parasitic nematodes in sugarcane in Japan. Greenhouse and field experiments were conducted to evaluate the efficacy of the phenylpyrazole insecticide fipronil (0.3–0.45 kg a.i./ha) against the root-lesion nematode, Pratylenchus zeae, which is an important plant-parasitic nematode species associated with sugarcane (Saccharum spp. hybrids) in Okinawa, Japan. Both experiments showed a reduction of P. zeae population densities in sugarcane roots to 27 to 56% of the non-treated control after 7 wk in the greenhouse experiment and 3 months in the field experiment (two trials). In contrast, P. zeae population densities in soil were not reduced by the fipronil treatment. At harvest, sugarcane yields in the field experiment were significantly increased by 6 to 8% in the fipronil treated plots compared to the non-treated control. The data showed that fipronil reduced numbers of P. zeae in sugarcane roots at the early stage of sugarcane seedling growth resulting in increased sugarcane yields. This is the first report of nematicidal activity of fipronil against P. zeae under field conditions.

Bolu İli Patates Üretim Alanlarında Bitki Paraziti Nematodların Belirlenmesi

Patates (Solanum tuberosum L.) dünyada insan beslenmesinde kullanılmak amacıyla yetiştiriciliği yapılan önemli tarımsal ürünlerden biri olup, başta bitki paraziti nematodlar (BPN) olmak üzere, birçok biyotik faktör patates yetiştiriciliğini önemli ölçüde sınırlandırmaktadır. Bu çalışma, Bolu ili patates üretim alanlarında patateste zararlı nematodların belirlenmesi amacıyla 2014-2016 yılları arasında yürütülmüştür. Çalışma sonucunda, Kök yara nematodları Pratylenchus spp. %52.5 oranla patates üretim alanlarında en fazla bulunan nematod olarak tespit edilmiştir. Kist nematodu, Globodera spp. %35, Kök-ur nematodu Meloidogyne spp. ise %20 oranında bulunmuş olup, münavebenin yapılmadığı lokasyonlarda bitki paraziti nematodların bulunma oranları: Ditylenchus %62,5 Geocenamus spp. %50, Helicotylenchus spp. or Rotylenchus spp. %40, for Paratylenchus ve Amplimerlinus spp. %30, Pratylenchoides spp. ve Tylenchorhynchus spp. %9 olarak tespit edilmiştir. Survey sonuçları, Bolu ili patates yetiştiriciliği yapılan alanlarda bitki paraziti nematodların yüksek yoğunlukta bulunduğu ve ekonomik ürün kayıplarına neden olabilecek potansiyele sahip olduğunu göstermektedir. Bu nedenle, Bolu ili patates üretim alanlarında bitki paraziti nematodların yaygınlık ve yoğunluğunu belirlemek amacıyla daha kapsamlı surveylerin yapılması, patateste zararlı nematodların, özellikle Globodera spp., Meloidogyne spp. ve Pratylenchus spp. türlerinin teşhislerinin yapılması gerekmektedir.

Исследования галловых нематод рода Meloidogyne (Goeldi, 1877) на территориях Болгарии и Российской Федерации

The purpose of the research is analysis of data on the species and racial composition of pathogenic nematodes of the genus Meloidogyne in Bulgaria and Russia. Materials and methods . The analysis of own and literary data on the distribution of root-knot nematodes on the territory of two countries was carried out. Results and discussion . Five species of Meloidogyne both under open-field and greenhouse conditions in Bulgaria were established (M. incognita, M. arenaria, M. javanica, M. hapla and M. thamesi). They successfully develop under greenhouse and open-field conditions and invade vegetables and ornamental plants. M. javanica predominantly develops under greenhouse conditions, but in South-Western part of Bulgaria it reproduces itself under open-field conditions and is one of the usual species of plant parasitic nematodes there. M. hapla is widespread both under greenhouse and open-field conditions. First in Bulgaria race 1 of M.arenaria was found. Investigations of M. hapla race composition found statistically reliable differences (length of stylet, length of J2, some differences of knobs morphology). On the territory of Russian Federation five species belonging to Meloidogyne were found (M. incognita, M. arenaria, M. javanica, M. hapla and M. ardenensis). The first three species develop only under greenhouse conditions and damage vegetables and ornamental plants. M. hapla is distributed from the most North-Western regions of Russia to the North Caucasus It successfully develops on the roots of all except cucumbers. At the time being Meloidogyne ardenensis has been found only on the roots of birch tree. M. hapla is distributed on the territories of the two countries with numerous hosts and which is very important – it damages potatoes. The results obtained investigations of M. hapla race composition are important for choice of the best methods for prevention and control.

Extraction of potato cyst nematodes from soil samples: Cobb’s decanting and sieving method vs. Fenwick’s method

Potato cyst nematodes are a threat to several agricultural crops around the world with some species considered quarantine pests and subjected to strict regulatory measures in many countries. Usually, cysts nematodes co-exist in the soil with other species of plant-parasitic nematodes, so, a time and cost-efficient extraction technique becomes of primary importance. The ideal extraction method should be able to obtain cysts as well as detecting the presence of other motile plant-parasitic nematodes with a potential impact on potato farming (such as Meloidogyne sp. and Pratylenchus sp.). In recent years, studies have been carried out to test the efficiency of various methods of nematode extraction but few results have been published. Therefore, to test if a method that extracts simultaneously cysts and motile nematodes can be used instead of the reference method that extracts cysts only, the efficiency of Cobb’s decanting and sieving technique was compared to Fenwick’s technique. As a result, in the 74 samples evaluated, a greater number of cysts were extracted from 24 samples using Fenwick’s method and from 11 samples employing Cobb’s decanting and sieving technique. The statistics results showed a significance level of 0,05 using Fenwick’s can allowing to conclude that this method is much more efficient than Cobb’s decanting and sieving technique, and confirming it should not be replaced by alternative methods for cysts extraction.

Impact of ethanedinitrile rates and application method on nutsedge species and tomato root galling

The pre-plant soil fumigant ethanedinitrile (EDN) has shown promising activity against several key pests including plant-parasitic nematodes, a variety of weeds, and soil-borne pathogens. With chemical properties similar to those of methyl bromide, EDN has the potential to move readily through the soil profile. EDN is being investigated as a pre-plant soil fumigant alternative to current industry standards for Florida plasticulture vegetable production. EDN was applied via shank injection, vapor, and drip irrigation. Control of nutsedge species and plant-parasitic nematode species was determined and compared to a non-treated control and a mixture of 39% 1,3-dichloropropene and 59.6% chloropicrin (1,3-D:Pic) in tomato and watermelon. In these studies, EDN performed as well as 1,3-D:Pic and significantly better than the nontreated control against nutsedge species. EDN applied as a vapor resulted in significantly increased nematode incidence at one location when compared with most other treatments.

Effect of the entomopathogenic nematode-bacterial symbiont complex on Meloidogyne hapla and Nacobbus aberrans in short-term greenhouse trials

Meloidogyne hapla and Nacobbus aberrans are plant-parasitic nematodes that form galls in the roots of infected plants and cause important economic losses. Entomopathogenic nematodes (EPNs) of the genera Steinernema and Heterorhabditis infect and kill insects via toxins produced by their symbiotic bacteria. EPNs have shown to have an antagonistic effect on different plant-parasitic nematode species in field and greenhouse trials. The aim of the present work was to evaluate, in tomato plants in greenhouse, the effect of the application of three Argentine EPN isolates, their symbiotic bacteria and cell-free supernatants, on a population of M. hapla and two populations of N. aberrans. Sixty days after inoculation, the number of galls and egg masses, the nematode reproduction factor (RF) and plant biomass were calculated. With a few exceptions, biomass was not affected by the different treatments. None of the plant-parasitic nematode populations was reduced by infective juvenile inoculation of the different EPN isolates. Bacterial action differed among populations; M. hapla was the most susceptible one, with a significant reduction in the number of galls, egg masses and RF caused by the application of the three bacterial strains. The most significant effect was produced by the cell-free supernatants on nematode RF, with reductions of 62–90%, caused by bacterial metabolites. The different inoculation alternatives of the EPN-bacterial symbiont complex tested in the present work (infective juveniles, bacteria and cell-free supernatant) are compared for the first time for plant-parasitic nematode species.

In vitro reproduction of Pratylenchus neglectus on carrot discs and investigation of its interaction with Meloidogyne hispanica on potato

Root-lesion nematodes, Pratylenchus spp., and root-knot nematodes, Meloidogyne spp., can occur concomitantly in potato fields and the interactions between the two groups of plant parasitic nematodes (PPN) may represent a threat to the potato crop. The in vitro reproductive fitness of 3 Portuguese isolates of P. neglectus isolated from potato fields was assessed using monoxenic carrot disc cultures inoculated with 10 females and maintained at 25 °C. The three isolates were able to reproduce at 56 days after inoculation (DAI) and the final population densities were significantly increased at 84 DAI. The P. neglectus isolate with the best reproductive ability was further selected and the concomitant effects of P. neglectus and M. hispanica were investigated in a pot trial using potato (Solanum tuberosum L.) cv. Agria as host. Single potato sprouts were inoculated with 250, 500, 750 and 1000 of either P. neglectus mixed stages/M. hispanica second-stage juveniles, or a combination of both nematodes. At 60 DAI, nematodes were extracted from roots and soil, the final population densities determined, for both nematode species, and the reproductive factor calculated. The experiment was run twice. The results suggest an additive effect of M. hispanica on P. neglectus reproduction, although future tests are still needed to confirm the possibility of an increase of P. neglectus population densities for the next crop, when both nematodes are inoculated concomitantly. The information obtained reinforces the need for a careful monitoring of these two PPN species in potato crops.