Root-knot Nematode Species Research Articles

Search for sources of genetic resistance to Meloidogyne enterolobii in tomato and in wild Solanum (section Lycopersicon) accessions

Meloidogyne enterolobii (syn. M. mayaguensis) is an emerging plant pathogen capable of inducing root galls and yield reduction in a wide range of host species. This pathogen has also been reported as a global threat for tomato (Solanum lycopersicum L.) crop production mainly due to its ability to overcome the Meloidogyne resistance meditated by the Mi-1 gene. Despite the potential importance of this nematode, sources of resistance to M. enterolobii are not yet available for breeding purposes. The main objective of the present work was to evaluate a large Solanum (section Lycopersicon) germplasm (comprising nine species and one botanic variety) aiming to identify useful sources of resistance to M. enterolobii. In the first screening assay, 101 accessions and the susceptible standard S. lycopersicum ‘Santa Cruz’ were inoculated and evaluated under controlled (greenhouse) conditions. Twenty-day-old seedlings were inoculated with a suspension of M. enterolobii eggs (710 eggs per plant) and maintained in expanded 128-cell polystyrene trays during the entire course of the experiment. The phenotypic criteria used for evaluation (done at 45 days after inoculation) were the number of root galls, gall index, number of eggs, and the reproduction factor. Twenty accessions with promising resistant reaction to M. enterolobii in the first screening test were selected and employed in a subsequent assay. Plants of the 20 selected accessions were cultivated in 400 cm3 pots filled with sterile soil. Inoculation procedures were identical to the first assay, but with higher inoculum pressure (3,300 eggs per plant). Three accessions with superior tolerance levels to M. enterolobii were identified viz. S. lycopersicum ‘Yoshimatsu’, S. lycopersicum ‘CNPH 1246’ and S. pimpinelifolium CGO 7650 (= CNPH 1195). These accessions were re-evaluated against a distinct M. enterolobii population as well as against two other root-knot nematode species (M. javanica and one M. incognita race 1). Under higher inoculum pressure, ‘Yoshimatsu’ was found to be resistant to M. javanica and M. incognita race 1, but susceptible to a M. enterolobii from guava. The other two sources displayed susceptibility to all three nematodes. The results indicated additional germplasm screening since no source of stable genetic resistance to M. enterolobii was found so far.

Biostimulants for Plant Growth Promotion and Sustainable Management of Phytoparasitic Nematodes in Vegetable Crops

The parasitism of root-knot nematodes, Meloidogyne spp., can cause heavy yield losses to vegetable crops. Plant biostimulants are often reported for a side-suppressive effect on these pests and many commercial products are increasingly included in sustainable nematode control strategies. Source materials of most biostimulants derived from plant or seaweed raw materials were documented for a reliable suppression of root-knot nematode species, whereas the suppressiveness of microbial biostimulants was found largely variable, as related to the crop and to environmental factors. Chitosan-based biostimulants were also stated for a variable phytonematode suppression, though clearly demonstrated only by a few number of studies. In a preliminary experimental case study, four commercial biostimulants based on quillay extract (QE), sesame oil (SO), seaweeds (SE), or neem seed cake (NC) were comparatively investigated for their effects against the root-knot nematode M. incognita on potted tomato. Soil treatments with all the four biostimulants resulted in a significant reduction of nematode eggs and galls on tomato roots, though NC and SO were significantly more suppressive than QE or SE. In addition, almost all biostimulant treatments also resulted in a significant improvement of tomato growth compared to the non-treated control. These preliminary results seem to confirm the literature data and clearly indicate the potential role of biostimulants for a safe nematode management both in organic and integrated crop systems.

First Report of Meloidogyne inornata on Smallanthus sonchifolius in Brazil

HomePlant DiseaseVol. 104, No. 2First Report of Meloidogyne inornata on Smallanthus sonchifolius in Brazil PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Meloidogyne inornata on Smallanthus sonchifolius in BrazilG. R. Camara, A. H. O. Carvalho, A. G. Teixeira, M. L. S. M. Ferreira, F. L. de Oliveira, W. B. Moraes, and F. R. AlvesG. R. Camara†Corresponding author: G. R. Camara; E-mail Address: camara.gdr@gmail.comhttp://orcid.org/0000-0001-8181-429XGraduate Program in Plant Production, UFES, 29500-000, Alegre, ES, BrazilSearch for more papers by this author, A. H. O. CarvalhoIFES, 29.395-000, Ibatiba, ES, BrazilSearch for more papers by this author, A. G. TeixeiraGraduate Program in Plant Production, UFES, 29500-000, Alegre, ES, BrazilSearch for more papers by this author, M. L. S. M. FerreiraGraduate Program in Plant Production, UFES, 29500-000, Alegre, ES, BrazilSearch for more papers by this author, F. L. de OliveiraDepartment of Agronomy, UFES, 29500-000, Alegre, ES, BrazilSearch for more papers by this author, W. B. Moraeshttp://orcid.org/0000-0001-7478-7772Department of Agronomy, UFES, 29500-000, Alegre, ES, BrazilSearch for more papers by this author, and F. R. AlvesDepartment of Agronomy, UFES, 29500-000, Alegre, ES, BrazilSearch for more papers by this author AffiliationsAuthors and Affiliations G. R. Camara1 † A. H. O. Carvalho2 A. G. Teixeira1 M. L. S. M. Ferreira1 F. L. de Oliveira3 W. B. Moraes3 F. R. Alves3 1Graduate Program in Plant Production, UFES, 29500-000, Alegre, ES, Brazil 2IFES, 29.395-000, Ibatiba, ES, Brazil 3Department of Agronomy, UFES, 29500-000, Alegre, ES, Brazil Published Online:30 Nov 2019https://doi.org/10.1094/PDIS-08-19-1739-PDNAboutSectionsSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat World production of yacon potatoes (Smallanthus sonchifolius Poepp. Endl) has increased by 140% in recent years (MAPA 2018). The generation of phytosanitary knowledge regarding nematodes is an immediate demand, considering the increase in the production of food and the scarcity of information about the causative agents of diseases in the culture (Gusso et al. 2015; Oliveira et al. 2013). In Brazil, two important pathogens have been reported on yacon: the fungus Fusarium oxysporum (Moraes et al. 2017) and the root-knot nematode (RKN) Meloidogyne ethiopica (Carneiro and Almeida 2005). Plants randomly collected from commercial farms located in the district of Alto Norte, Muniz Freire, Espírito Santo, Brazil (20°14′39.0″S, 41°24′43.1″W), distributed in the field at a regular dispersion gradient, showed uniformly intense leaf yellowing (leaf chlorosis) symptoms, distributed on the leaf surface, especially in the lower leaves, small size (dwarfism), wilting at the hottest hours of the day, and galls throughout the plant root system. Phytonematodes were identified parasitizing absorption roots, tuberous roots, and rhizophores of S. sonchifolius. With the main purpose of multiplication the RKN species, 12 egg masses were individually collected from the absorption roots, tuberous roots, and rhizophores of S. sonchifolius and macerated in Eppendorf tubes (5 ml) containing distilled sterilized water and were inoculated in 12 tomato seedlings (Solanum lycopersicum ‘Santa Clara’) kept in pots containing a sterile mixture of soil, sand, and manure in a ratio of 2:1:1. The pots with tomato seedlings were kept in a greenhouse for 60 days under the same conditions of soil (a sterile mixture), temperature (28 ± 5°C), and humidity. With the main purpose extraction of the RKN species and reproduction of the symptoms observed in the field, 12 egg masses were individually collected from the tomato roots and macerated in Eppendorf tubes (5 ml) containing distilled sterilized water and were inoculated in 12 absorption roots and tuberous roots of S. sonchifolius kept in pots containing a sterile mixture of soil, sand, and manure in a ratio of 2:1:1. The pots with S. sonchifolius seedlings were kept in a greenhouse for 60 days under the same conditions of soil (a sterile mixture), temperature (28 ± 5°C), and humidity to reproduce the symptoms observed in the field, fulfilling Koch’s postulates. The final population density (Pf) of phytonematodes was quantified, being higher than the initial population density (Pi – inoculated). Only the inoculated plants showed the same typical symptoms observed in S. sonchifolius plants collected in the field. The biochemical technique of isoenzyme electrophoresis was used for the identification (Carneiro and Almeida 2001). Eight young females extracted from infected yacon potato roots were macerated in Eppendorf tubes (5 ml) containing distilled sterilized water, and a species-specific enzyme phenotype I3 (Rm: 0.8, 1.1, 1.25) was identified, corresponding to M. inornata recently considered as a species belonging to M. ethiopica group (Gerič Stare et al. 2019). A protein extract of M. javanica was included as a reference. It is concluded, therefore, that the causal agent of the observed field symptoms in the Alto Norte district, Muniz Freire, Espírito Santo, Brazil, is due to M. inornata parasitism. This is the first report of M. inornata officially diagnosed causing damage to commercial production of S. sonchifolius in Brazil.The author(s) declare no conflict of interest.

The quarantine root‐knot nematode Meloidogyne enterolobii – a potential threat to Portugal and Europe

In 2017, during a survey on subsistence farms and gardens in Coimbra region, Portugal, 40 infected root samples were collected and 47 root‐knot nematode (RKN) isolates identified, based on esterase phenotype. The phenotypes A2, H1, Hi2/Hi4, I1/I2/I3 and J3 associated to five Meloidogyne species (M. arenaria, M. hapla, M. hispanica, M. incognita and M. javanica) were found in 43 RKN isolates. The esterase phenotype En2/En4/En5, corresponding to M. enterolobii (=M. mayaguensis), was detected in four RKN isolates from Cereus hildmannianus (Cactaceae), Lampranthus sp. (Aizoaceae), Physalis peruviana (Solanaceae) and Callistemon sp. (Myrtaceae) infected roots. In order to validate the biochemical identification of the M. enterolobii isolates, molecular studies performed with species‐specific primers yielded the expected fragment of c.520 bp, and the amplification of cytochrome oxidase subunits I and II regions of 800 bp. The DNA sequences of one of the isolates were compared with available Meloidogyne species sequences in databases. The Portuguese isolate grouped with 99–100% bootstrap support with all M. enterolobii sequences included for comparison, confirming the presence of this RKN species in Portugal. In the EPPO region, M. enterolobii has been reported in France and Switzerland and intercepted in the Netherlands, Germany and the UK associated with plant material from Asia, South America and Africa. Taking into account the pathogen aggressiveness and its distribution, there is a high probability of its spread not only in the Mediterranean region but also in Europe, and of it becoming a threat to the agricultural economy, where there are no effective strategies for its control.

Prevalence and Distribution of Plant-Parasitic Nematodes Associated with Doum Palm Trees Hyphaene thebaica (L.) Mart. in Aswan Southern Egypt with Emphasis on Biochemical and Molecular Identification of Root-Knot Nematode

An intensive field study was carried out during the period from December, 27th 2016 to November, 3rd 2017 to survey nematode associations of doum palm trees, Hyphaene thebaica in Aswan governorate, Southern Egypt. In this regard, a total of 105 composite rhizosphere soil and root samples were collected from different provinces (Aswan, Daraw, Edfu and Kom Ombo) belonging to Aswan governorate. Nematodes were extracted by Cobb’s wet-sieving and centrifugal sugar flotation techniques and identified to the genus level according to the original body descriptions and standard identification keys of plant-parasitic nematodes. Fourteen genera were found to be associated with the rhizosphere of doum palms and could be descendly arranged based on their frequency of occurrence (FO%) as follows: Meloidogyne (46.7%), Rotylenchulus (33.3%), Helicotylenchus (27.6%), Aphelenchus (17.1%), Tylenchus (14.3%),Hemicriconemoides (12.4%), Tylenchorhynchus (9.5%), Ditylenchus (8.6%), Aphelenchoides (7.6%), Pratylenchus (6.7%), Trichodorus (5.7%), Criconemella (4.8%), Paratylenchus (3.8%) and Hoplolaimus (2.9%). It was clearly noticed that root-knot (Meloidogyne), reniform (Rotylenchulus) and spiral (Helicotylenchus) nematodes appeared to be the most prominent genera recording high prominence value (PV) reaching 3444, 2816 and 1902, respectively and population density (PD) 504, 488 and 362 nematodes/250 cc3 soil, consequently, whereas the rest genera were less prominent representing PV ranging between 109-595 with PD reaching 46-201 nematodes/250 cc3 soil. Examination of root samples revealed the presence of ideal root galling caused by Meloidogyne and their sedentary adult females were isolated and subjected to the traditional identification to the species level using perineal pattern test and reconfirmed by the biochemical and molecular identification methods. Meloiodogyne javanica appeared to be the predominant root-knot nematode species in this study. The current results updated the database of nematode associations with their plant hosts in Egypt and introduced doum palm as new host of M. javanica and probably to other nematodes.

Search for sources of resistance to Meloidogyne enterolobii in commercial and wild tomatoes

ABSTRACT Meloidogyne enterolobii (=M. mayaguensis) is an emerging plant pathogen capable of inducing root galls and yield reduction in a wide range of host species. This pathogen has also been reported as a global threat for tomato (Solanum lycopersicum) crop production mainly due to its ability to overcome the resistance meditated by the Mi-1 gene. Despite the potential importance of this nematode, sources of resistance to M. enterolobii are not yet available for breeding purposes. The main objective of the present work was to evaluate a large Solanum (section Lycopersicum) germplasm (comprising nine species and one botanic variety) aiming to identify useful sources of resistance to M. enterolobii. In the first screening assay, 101 accessions and the susceptible standard S. lycopersicum ‘Santa Cruz’ were inoculated and evaluated under controlled conditions. The phenotypic criteria used for evaluation were the number of root galls, gall index, number of eggs, and the reproduction factor. Plants of the 20 selected accessions were cultivated in 0.4 L pots filled with sterile soil. Inoculation procedures were identical to the first assay, but with higher inoculum pressure (3,300 eggs per plant). Three accessions with superior tolerance levels to M. enterolobii were identified viz. S. lycopersicum ‘Yoshimatsu’, S. lycopersicum ‘CNPH 1246’ and S. pimpinelifolium CGO 7650 (= CNPH 1195). These accessions were re-evaluated against a distinct M. enterolobii population as well as against two other root-knot nematode species (M. javanica and one M. incognita race 1). Under higher inoculum pressure, ‘Yoshimatsu’ was found to be resistant to M. javanica and M. incognita race 1, but susceptible to M. enterolobii from guava. The other two sources displayed susceptibility to all three nematodes. Additional germplasm screening is needed since no source of stable genetic resistance to M. enterolobii was found so far.

Gene copy number variations as signatures of adaptive evolution in the parthenogenetic, plant-parasitic nematode Meloidogyne incognita.

Adaptation to changing environmental conditions represents a challenge to parthenogenetic organisms, and until now, how phenotypic variants are generated in clones in response to the selection pressure of their environment remains poorly known. The obligatory parthenogenetic root-knot nematode species Meloidogyne incognita has a worldwide distribution and is the most devastating plant-parasitic nematode. Despite its asexual reproduction, this species exhibits an unexpected capacity of adaptation to environmental constraints, for example, resistant hosts. Here, we used a genomewide comparative hybridization strategy to evaluate variations in gene copy numbers between genotypes of M.incognita resulting from two parallel experimental evolution assays on a susceptible vs. resistant host plant. We detected gene copy number variations (CNVs) associated with the ability of the nematodes to overcome resistance of the host plant, and this genetic variation may reflect an adaptive response to host resistance in this parthenogenetic species. The CNV distribution throughout the nematode genome is not random and suggests the occurrence of genomic regions more prone to undergo duplications and losses in response to the selection pressure of the host resistance. Furthermore, our analysis revealed an outstanding level of gene loss events in nematode genotypes that have overcome the resistance. Overall, our results support the view that gene loss could be a common class of adaptive genetic mechanism in response to a challenging new biotic environment in clonal animals.

Host-induced silencing of Mi-msp-1 confers resistance to root-knot nematode Meloidogyne incognita in eggplant.

RNA interference (RNAi)-based host-induced gene silencing (HIGS) is emerging as a novel, efficient and target-specific tool to combat phytonematode infection in crop plants. Mi-msp-1, an effector gene expressed in the subventral pharyngeal gland cells of Meloidogyne incognita plays an important role in the parasitic process. Mi-msp-1 effector is conserved in few of the species of root-knot nematodes (RKNs) and does not share considerable homology with the other phytonematodes, thereby making it a suitable target for HIGS with minimal off-target effects. Six putative eggplant transformants harbouring a single copy RNAi transgene of Mi-msp-1 was generated. Stable expression of the transgene was detected in T1, T2 and T3 transgenic lines for which a detrimental effect on RKN penetration, development and reproduction was documented upon challenge infection with nematode juveniles. The post-parasitic nematode stages extracted from the transgenic plants showed long-term RNAi effect in terms of targeted downregulation of Mi-msp-1. These findings suggest that HIGS of Mi-msp-1 enhances nematode resistance in eggplant and protect the plant against RKN parasitism at very early stage.

A Novel Root-Knot Nematode Resistance QTL on Chromosome Vu01 in Cowpea.

The root-knot nematode (RKN) species Meloidogyne incognita and M. javanica cause substantial root system damage and suppress yield of susceptible cowpea cultivars. The narrow-based genetic resistance conferred by the Rk gene, present in some commercial cultivars, is not effective against Rk-virulent populations found in several cowpea production areas. The dynamics of virulence within RKN populations require a broadening of the genetic base of resistance in elite cowpea cultivars. As part of this goal, F and F populations from the cross CB46-Null (susceptible) x FN-2-9-04 (resistant) were phenotyped for M. javanica induced root-galling (RG) and egg-mass production (EM) in controlled growth chamber and greenhouse infection assays. In addition, F families of the same cross were phenotyped for RG on field sites infested with Rk-avirulent M. incognita and M. javanica. The response of F to RG and EM indicated that resistance to RKN in FN-2-9-04 is partially dominant, as supported by the degree of dominance in the F and F populations. Two QTL associated with both RG and EM resistance were detected on chromosomes Vu01 and Vu04. The QTL on Vu01 was most effective against aggressive M. javanica, whereas both QTL were effective against avirulent M. incognita. Allelism tests with CB46 x FN-2-9-04 progeny indicated that these parents share the same RKN resistance locus on Vu04, but the strong, broad-based resistance in FN-2-9-04 is conferred by the additive effect of the novel resistance QTL on Vu01. This novel resistance in FN-2-9-04 is an important resource for broadening RKN resistance in elite cowpea cultivars.

Grass Root-Knot Nematode Meloidogyne graminis Whitehead, 1968 (Nematode: Tylenchida: Meloidogynidae)


 
 Root-knot nematodes (Meloidogyne spp.) are the most important plant-parasitic nematodes worldwide, with most temperate and tropical crops suffering yield losses from one or more species of Meloidogyne. Root-knot nematodes are the most widely recognized plant-parasitic nematodes because the characteristic galls or knots they cause on plant roots are easily observed symptoms for diagnosis. Meloidogyne graminis is damaging to many turf and forage grasses. Due to the prevalence of this nematode on grasses, and the prevalence of grasses compared to other crops in the state, it is likely the most widespread species of root-knot nematode in Florida. It is of increasing concern due to the rising importance of turfgrasses in the Florida economy, the susceptibility of grasses to this nematode, and implementation of new diagnostic techniques that have brought to light the damaging potential of this nematode.
 This document is also available on the Featured Creatures website at http://entomology.ifas.ufl.edu/creatures.
 https://edis.ifas.ufl.edu/in1231

New Data Completing the Spectrum of theMa,RMia, andRMjaGenes for Resistance to Root-Knot Nematodes (Meloidogynespp.) inPrunus

Root-knot nematodes (RKN) (Meloidogyne spp.) are worldwide pests that affect a considerable number of plants, among which stone fruit (Prunus spp.) are severely attacked. Prevalent RKN species are Meloidogyne arenaria, M. incognita, and M. javanica in stone fruit but the emergent M. ethiopica and M. enterolobii are also reported to challenge perennial crops. In Prunus spp., the complete-spectrum resistance (R) gene Ma from plum and the more restricted-spectrum R genes RMia from peach and RMja from almond completely inhibit nematode multiplication and gall formation of the RKN species that they control. This study aimed to update the resistance spectra of these three major genes by evaluating their activity toward one isolate of the yet-untested RKN species mentioned above. To state whether a given gene controls a particular species, the principle of our experiment was to genotype with appropriate markers a number of individuals segregating for this gene and then to phenotype these individuals. A perfect matching of the genotype and the phenotype of individuals indicates that the gene of interest is active against and, thus, controls the corresponding isolate of this RKN species. Segregating materials used were an Ma F1 plum progeny, an RMia F2 peach progeny, and an RMja F2 almond progeny. In addition to previous data, our results establish a clear spectrum for each of the three genes toward isolates from both the three prevalent species and the two emerging species. Ultimately, our results reveal that (i) Ma controls all of them, (ii) RMja controls all species except M. incognita and M. floridensis, and (iii) RMia controls M. arenaria, M. incognita, and M. ethiopica but not M. javanica or M. enterolobii. Our data should have wide implications for RKN resistance management and breeding and for deciphering the molecular mechanisms of the spectrum of RKN R genes.

On the Close Relatedness of Two Rice-Parasitic Root-Knot Nematode Species and the Recent Expansion of Meloidogyne graminicola in Southeast Asia.

Meloidogyne graminicola is a facultative meiotic parthenogenetic root-knot nematode (RKN) that seriously threatens agriculture worldwide. We have little understanding of its origin, genomic structure, and intraspecific diversity. Such information would offer better knowledge of how this nematode successfully damages rice in many different environments. Previous studies on nuclear ribosomal DNA (nrDNA) suggested a close phylogenetic relationship between M. graminicola and Meloidogyne oryzae, despite their different modes of reproduction and geographical distribution. In order to clarify the evolutionary history of these two species and explore their molecular intraspecific diversity, we sequenced the genome of 12 M. graminicola isolates, representing populations of worldwide origins, and two South American isolates of M. oryzae. k-mer analysis of their nuclear genome and the detection of divergent homologous genomic sequences indicate that both species show a high proportion of heterozygous sites (ca. 1–2%), which had never been previously reported in facultative meiotic parthenogenetic RKNs. These analyses also point to a distinct ploidy level in each species, compatible with a diploid M. graminicola and a triploid M. oryzae. Phylogenetic analyses of mitochondrial genomes and three nuclear genomic sequences confirm close relationships between these two species, with M. graminicola being a putative parent of M. oryzae. In addition, comparative mitogenomics of those 12 M. graminicola isolates with a Chinese published isolate reveal only 15 polymorphisms that are phylogenetically non-informative. Eight mitotypes are distinguished, the most common one being shared by distant populations from Asia and America. This low intraspecific diversity, coupled with a lack of phylogeographic signal, suggests a recent worldwide expansion of M. graminicola.

Response of two Citrullus amarus accessions to isolates of three species of Meloidogyne and their graft compatibility with watermelon

The response of two Citrullus amarus accessions, BGV0005164 and BGV0005167, was assessed against different Meloidogyne arenaria, Meloidogyne incognita, and Meloidogyne javanica isolates in pot experiments and against M. incognita in plastic greenhouse. In the pot experiments, plants were inoculated with a second-stage juvenile per cm3 of sterile sand and maintained in a growth chamber at 25 °C for 50 days. The watermelon cv. Sugar Baby was included as a susceptible control for comparison. At the end of the experiments, the number of egg masses and eggs per plant was determined, and the reproduction index was calculated as the percentage of the number of eggs produced in the C. amarus accessions with regard to that produced in the susceptible cv. Sugar Baby. In the plastic greenhouse experiment, the ungrafted watermelon cv. Sugar Baby and watermelons grafted onto each of the C. amarus accessions and onto the watermelon rootstock cv. Robusta were cultivated from May to August 2016 in plots with nematode densities from 46 to 1392 J2 per 250 cm3 of soil at transplantation. At the end of the experiment, the galling index and the number of eggs per plant were determined, and the reproduction index was calculated. Additionally, the compatibility of the two accessions with the watermelon cv. Sugar Baby and the effect on fruit quality (weight, size, shape, firmness, pH, total soluble solids, and flesh color) were assessed under a hydroponic system in a greenhouse. The commercial rootstocks cv. Cobalt and cv. Robusta were also included. All the Meloidogyne isolates produced less egg masses and eggs per plant on the accessions than on Sugar Baby. Both accessions performed as resistant against M. arenaria, and from highly to moderately resistant to M. incognita and M. javanica in pot experiments. In the plastic greenhouse experiment, both C. amarus accessions performed as resistant to M. incognita. Both C. amarus accessions were compatible with the watermelon cv. Sugar Baby, but only the BGV0005167 accession did not influence the fruit quality. Then, the BGV0005167 accession is a promising rootstock for managing the three tropical root-knot nematode species without influencing watermelon fruit quality.

Genetic Variability among Different Populations of Root Knot Nematodes Based on Their Encumbrance Response to Pasteuria Isolates Using PCR-RFLP

A great variable response was observed when PP-3 and PP-J encumbered with 116 populations of root knot nematode (RKN) at two different temperatures (25 ± 2°C and 30 ± 2°C) and concentrations (104 and 105 spores/ml). The PCR reaction amplified intergenic region between cytochrome oxidase subunit II gene (COII) and large subunit of rRNA gene (lrRNA) of the mitochondrial genome of different RKN species. The primer C2F3 and 1108 identified M. incognita with the highest frequency (52.6%) followed by M. javanica (36.8%) and M. arenaria (10.5%). The sizes of PCR products were 1.7 kb for M. incognita and M. javanica populations while populations of M. arenaria produced 1.1 kb fragment. The digestion with Hinf I yielded three different fragment length patterns on 1.5 % agarose gel. From current research it is concluded that intra-Meloidogyne genetic variability exist in RKN populations which have better encumbrance with P. penetrans.

Recognition of species belonging to Meloidogyne ethiopica group and development of a diagnostic method for its detection

Root-knot nematodes (RKN) of the tropical group reproducing as a rule with mitotic parthenogenesis are highly polyphagous and damaging pests causing great losses in crop production. Morphometrical and molecular characters of three closely related tropical RKN species have been analysed in order to identify species-specific diagnostic parameters and examine the relationship between species. Morphometrical characters of M. ethiopica, M. luci and M. inornata isolates were similar and overlapped when compared between species and isolates of the same species indicating a very close relationship between the three species. Additionally, structure of map-1 genes was analysed, which provided the evidence of identical structure of map-1 family genes in M. ethiopica, M. inornata and M. luci. The unique structure of map-1 genes when compared to the other tropical RKN species further supports close relationship of the three species and therefore we have classified them together as M. ethiopica group. In addition, our results showed that the emergence of a virulent M. luci population does not correlate with the loss of map-1 genes as it was previously indicated for M. incognita (Castagnone-Sereno et al. 2009). Further, we have developed novel molecular methods to aid in identification of these nematodes: a PCR based method with primers specific for the M. ethiopica group comprising M. ethiopica M. luci and M. inornata, and a PCR based method with primers specific for the tropical RKN group species. Our results show that species of Meloidogyne ethiopica group share high similarity at morphological and genetic level.

Meloidogyne Species Associated with Weeds in Rio Grande do Sul

ABSTRACT: The frequency of species of root-knot nematodes (Meloidogyne spp.) was evaluated in weeds collected in different fallow farms in the State of Rio Grande do Sul, Brazil. In the samples where the nematode was found, the species of the root-knot nematode was identified by electrophoresis using the isozyme esterase. They were obtained from weeds belonging to 24 weed species from 13 different botanical families: Amaranthaceae, Asteraceae, Commelinaceae, Convovulaceae, Cyperaceae, Euphorbiaceae, Lamiaceae, Malvaceae, Oxalidaceae, Poaceae, Portulacaceae, Solanaceae, Verbenaceae. Meloidogyne javanica Est J3 (Rm: 1.0, 1.25, 1.40) was the most frequent species and occurred in 53.3% of the samples. M. arenaria with phenotype Est. A2 (Rm: 1.20, 1.30) was detected in 15.6% of the samples. M. incognita Est. I2 (Rm: 1.0, 1.1), M. ethiopica Est. E3 (Rm: 0.9, 1.15, 1.30), M. enterolobii Est. M2 (Rm: 0.7, 0.75, 0.9, 0.95) and M. hapla Est. H1 (Rm: 1.17) in 13.3%, 8.9%, 6.7% and 2.2% of the samples, respectively. Therefore, knowledge of the range of host plants to different species of the root-knot nematode can positively contribute to the adoption of management practices that allow the reduction of their populations in the soil.

Biological attributes of Salibro™, a novel sulfonamide nematicide. Part 1: Impact on the fitness of Meloidogyne incognita, M. hapla and Acrobeloides buetschlii

Summary Salibro™ is a novel sulfonamide nematicide containing the active substance (a.s.) fluazaindolizine (Reklemel™ active). Its biochemical mode of action is presently unknown but in internal laboratory studies it exerted adverse effects on various fitness parameters (motility, mobility and infectivity) of two species of root-knot nematodes (Meloidogyne incognita and M. hapla). While not causing an immediate knock-down effect on second-stage juveniles (J2) during the first 24-48 h of exposure to concentrations of 1-50 ppm (a.s.), exposed J2 showed clearly visible symptoms of toxicological effects (including characteristic body postures) and started to lose both their mobility as well as infectivity. This decrease in mobility and infectivity was nonreversible, even if the J2 were washed, and was already observed after pre-exposure periods of 24-48 h at 1-50 ppm (a.s.). Lower temperatures during the exposure period (4-10°C) did not prevent toxicological effects of treated J2 but slightly delayed the time-to-effect. By contrast, various vermiform life-stages of the bacteriophagous nematode, Acrobeles buetschlii, did not show any signs of intoxication or reduced motility during continuous exposure to Salibro™ at up to 250 ppm (a.s.). Salibro™ slightly increased hatching of M. hapla but did not significantly impact the hatching of M. incognita at concentrations up to 50 ppm (a.s.). No adverse effects on hatching were observed for A. buetschlii at concentrations up to 250 ppm (a.s.). The results indicate that Salibro™ is an effective and selective nematicide and will be a useful new tool in sustainable nematode management.

First report of Meloidogyne javanica on Ginger and Turmeric in the United States.

Ginger (Zingiber officinale L.) and turmeric (Curcuma longa L.) are two her baceous perennial plant species with rhizomes that are commonly used for flavoring or medicinal purposes. In January 2018, stunting and poorly developed root systems typically associated with plant-parasitic nematode infection were observed on organically grown edible ginger and turmeric in a hoop house in Wheeler County, Georgia. Examination of soil and root samples from symptomatic plants revealed the presence of high populations of root-knot nematodes (Meloidogyne spp.). The second-stage juveniles (J2s) were extracted from soil samples as described by Jenkins (1964). Nematode counts were 285 and 155 J2s per 100 cm3 soil in the areas planted with ginger and turmeric, respectively. Nematode eggs were recovered from infected root systems using the bleach (1%) and blending method (Hussey and Barker, 1973). Examination of the root samples showed the presence of 840 and 320 eggs per g of roots in ginger and turmeric, respectively. Primary diagnosis of the Meloidogyne specimens was done by comparing morphological features observed in the J2s (n = 10) and perineal pattern of females (n = 11) based on the description given by Eisenback and Triantaphyllou (1991) and were tentatively identified as M. javanica (Treub, 1885; Chitwood, 1949). For species identification, DNA sequencing was performed using multiple markers located in 18S ribosomal RNA and 5.8S internal transcribed spacer 1 regions, (18S + ITS) (GenBank Accession No. MK390613), 28S domain 2 and 3 (28S D2/D3) (MK385596), cytochrome oxidase subunit I (COI) (MK391558), and subunit II and 16S (COII + 16S) (MK391557) of mitochondrial DNA following methods as described in Ye et al. (2015). PCR assays by species-specific primers were also conducted to confirm species identity as described by Zijlstra et al. (2000).The blast search results of DNA sequences of 18S + ITS, 28S (D2/D3), COI and COII + 16S revealed the best match as M. javanica, M. incognita (Kofoid and White, 1912; Chitwood, 1949) and M. arenaria (Neal, 1889; Chitwood, 1949) with 99–100% identity. These genes are highly conserved across these three most common root-knot nematode species. However, results of PCR assays by species-specific primers were only positive for M. javanica using primers Fjav/Rjav, but negative for M. incognita by Finc/Rinc and M. arenaria by Far/Rar as described by Zijlstra et al. (2000). Based on morphological characteristics and molecular analyses, the root-knot nematodes infecting ginger and turmeric were identified as M. javanica. After confirmation of the nematode species, a test was conducted in the greenhouse to assess the pathogenicity of the nematode on ginger and turmeric. Five seedlings per plant species (cultivars unknown) were grown in 15 cm-diam plastic pots containing equal parts of pasteurized field soil and sand, and then inoculated with 2,000 eggs of M. javanica. The egg suspension was added into three holes around the base of each seedling. Non-inoculated seedlings (n2 = 25) were used as controls. Plants were arranged in completely randomized design and grown at 25 ± 3 °C for 10 weeks. At the termination of the experiment, small galls were noticed on the roots of the inoculated seedlings of both ginger and turmeric. No galls were observed on the roots of non-inoculated plants. Egg were extracted from the galled roots (Hussey and Barker, 1973) yielding an average of 1040 ± 96 and 732 ± 54 eggs per g of root of ginger and turmeric, respectively. On ginger, the nematode produced large numbers of galls and egg masses on both primary and secondary (feeder) roots, but the galls produced on turmeric were often observed only on primary roots (Fig. 1). No symptoms of root-knot nematode infestation including galls or water-soaked lesions were observed on the outer surface of rhizomes of both ginger and turmeric. However, the size of rhizomes in the M. javanica-infested areas was visibly smaller than that in non-infested areas (Fig. 2). A similar reduction in the growth of turmeric rhizomes was also observed. Meloidogyne incognita has been commonly reported as a nematode pest of ginger (Myers et al., 2017) and turmeric (Hall et al., 2017) in the USA and both M. incognita and M. javanica are known to cause damage on these plant hosts (Ray et al., 1995; Singh and Gupta, 2011). To the best of our knowledge, this is the first report of M. javanica on ginger and turmeric in the USA.

Green synthesis of silver nanoparticles using latex extract of Euphorbia tirucalli: A novel approach for the management of root knot nematode, Meloidogyne incognita

In recent years, research on novel nematicides has gained great interest to reduce world crop losses caused by plant parasitic nematodes. In this study, we explored the synthesis of silver nanoparticles (Et-AgNPs) by using latex extract of Euphorbia tirucalli against root-knot nematode species, Meloidogyne incognita. The physico-chemical properties of newly synthesized Et-AgNPs were determined using UV–Vis spectroscopy, Field Emission Scanning Electron Microscopy (FE-SEM), Fourier-Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction (XRD). The nematicidal activity of Et-AgNPs against second stage juveniles (J2) of M. incognita was tested based on in-vitro (mortality and hatching) and in-planta trials (infectivity and crop protection) at different concentrations. The findings indicated that Et-AgNPs were lethal to J2 and also inhibited egg hatching (in-vitro). In-planta trials suggest that infestation on tomato roots was significantly reduced when the Et-AgNPs were applied as a root dip treatment. Tomato plants treated with Et-AgNPs had healthier growth parameters with a concurrent reduction in overall gall formation, egg masses on roots, number of eggs per egg mass and J2 populations within the plants. From this study, it was concluded that Et-AgNPs are helpful for the management of M. incognita and will be an effective replacement for synthetic nematicides.

Short Communication: The prevalence and species of root-knot nematode which infect on potato seed in Central Java, Indonesia

Mutala’liah, Indarti S , Wibowo A. 2019. Short Communication: The prevalence and species of root-knot nematode which infect on potato seed in Central Java, Indonesia. Biodiversitas 20: 11-16. Root-knot nematodes are considered as one of the most destructive pathogens of potatoes, especially on tuber seed. Infected potato seed will cause tuber malformation and the most important thing is as the main spreading source of Meloidogyne spp. The objective of this research was to know the prevalence and identify the species of root-knot nematode which attack the potato seed in four sub-districts of potato production centre in Central Java, Indonesia. Molecular and morphological identification was conducted for the nematode species identification. PCR assay using MIG primer to detect three tropical root-knot nematodes followed by sequencing was conducted for molecular detection, while the perennial pattern was conducted for morphological detection. Results showed that root-knot nematodes on potato seed were generally distributed in Central Java with the prevalence percentage between 14.28-88.23% on the three from four sampling area. The molecular and morphological identification show that species of root-knot nematodes identified on potato seeds were Meloidogyne javanica, M. incognita, and M. arenaria.