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A new root‐knot nematode (RKN), Meloidogyne izalcoensis, was detected on coffee in Brazil. This species was first described on coffee from El Salvador and later detected in Asia and Africa. There are no reports on the genetic diversity of this species and resistance to M. izalcoensis has not yet been studied in coffee cultivars. All populations were identified by esterase phenotype and sequence‐characterized amplified region (SCAR) species‐specific markers. Based on random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) markers, low intraspecific variability was detected among M. izalcoensis populations from Africa, Vietnam and Brazil, but the population from El Salvador showed fewer genetic differences from the other populations. Phylogenetically, all populations of M. izalcoensis from different locations (El Salvador, Kenya, Tanzania, Vietnam and Brazil) grouped with 90% and 69% bootstrap support for COII and HSP90 regions, respectively, indicating that these markers are highly conserved for the species. In addition, both markers enabled separation of M. izalcoensis populations from other important coffee Meloidogyne species, including M. exigua, M. paranaensis, M. incognita, M. arabicida and M. lopezi. In resistance studies, most genotypes tested that had resistance to other Meloidogyne spp. (Amphillo × Catuaí, Hybrid of Timor, IAPAR 59, IPR 99, IPR 100, IPR 102, IPR 103, IPR 105, IPR 106, IPR 107 and IPR 108) were found to be susceptible to M. izalcoensis, except for the rootstock cv. Apoatã IAC 2258, which proved to be moderately resistant, with a genetic segregation for this character of 43.8%. [ABSTRACT FROM AUTHOR]

Very effective genetic control of some root-knot nematode (RKN) species (Meloidogyne spp.) is obtained by the employment of the tomato (Solanum lycopersicum L.) dominant Mi-1.2 gene. However, the phenotypic expression conferred by the Mi-1.2 gene may be impaired by high soil temperatures (above 28 °C) and by previously reported virulent RKN species and/or populations. Here, a putative Mi-1.2 gene-virulent RKN population was found inducing severe gall symptoms in roots of the tomato rootstock 'Guardião' (a homozygous Mi-1.2 hybrid of S. lycopersicum × S. peruvianum) under protected crop conditions in Southern Brazil. Females were extracted from severely infected roots displaying large galls and used for biochemical characterization of α-esterase (EST) and confirmed by SCAR markers. Additional pathogenicity assays were carried out in order to confirm the virulence (= resistance-breaking) feature of this RKN population by employing other or the same Mi-1.2 gene-carrying rootstocks. This virulent RKN population was identified as M. javanica (EST J3 and J2). The pathogenicity tests confirmed that this M. javanica population can overcome the Mi-1.2 resistance gene, and it is able to induce severe root-gall symptoms and to reproduce in two dominant resistant rootstocks ('Muralha' and 'Guardião') under greenhouse conditions. In addition, an initial inoculum of 2000–7000 eggs was considered ideal for future studies with the virulent M. javanica population. It is the first report of a Mi-1.2 gene-virulent M. javanica population in Brazil, which may represent a potential threat to the tomato agribusiness sector. [ABSTRACT FROM AUTHOR]

The root‐knot nematodes are the most devastating worms to worldwide agriculture with Meloidogyne incognita being the most widely distributed and damaging species. This parasitic and ecological success seems surprising given its supposed obligatory clonal reproduction. Clonal reproduction has been suspected based on cytological observations but, so far, never confirmed by population genomics data. As a species, M. incognita is highly polyphagous with thousands of host plants. However, different M. incognita isolates present distinct and overlapping patterns of host compatibilities. Historically, four "host races" had been defined as a function of ranges of compatible and incompatible plants. In this study, we used population genomics to assess whether (a) reproduction is actually clonal in this species, (b) the host races follow an underlying phylogenetic signal or, rather represent multiple independent transitions, and (c) how genome variations associate with other important biological traits such as the affected crops and geographical distribution. We sequenced the genomes of 11 M. incognita isolates across Brazil that covered the four host races in replicates. By aligning the genomic reads of these isolates to the M. incognita reference genome assembly, we identified point variations. Analysis of linkage disequilibrium and 4‐gametes test showed no evidence for recombination, corroborating the clonal reproduction of M. incognita. The few point variations between the isolates showed no significant association with the host races, the geographical origin of the samples, or the crop on which they have been collected. Addition of isolates from other locations around the world confirmed this lack of underlying phylogenetic signal. This suggests multiple gains and losses of parasitic abilities and adaptations to different environments account for the broad host spectrum and wide geographical distribution of M. incognita and thus to its high economic impact. This surprising adaptability without sex poses both evolutionary and agro‐economic challenges. [ABSTRACT FROM AUTHOR]

Root-knot nematodes (Meloidogyne spp.) significantly impact potato production worldwide and in Brazil they are considered one of the most important group of nematodes affecting potatoes. The objectives of this study were to survey Meloidogyne spp. associated with potatoes in Brazil, determine their genetic diversity and assess the aggressiveness of M. javanica on two susceptible potato cultivars. Fifty-seven root-knot nematode populations were identified using esterase phenotyping, including Meloidogyne javanica, M. incognita, M. arenaria and M. ethiopica. Overall, root-knot nematodes were present in ca 43% of sampled sites, in which M. javanica was the most prevalent species, and the phenotypes Est J3, J2a and J2 occurred in 91.2, 6.7 and 2.1% of the positive samples, respectively. Other species, such as M. incognita, M. arenaria and M. ethiopica, were found less frequently and occurred at rates of 6.4, 4.3 and 2.1% of the samples, respectively. Sometimes, M. javanica was found in mixtures with other root-knot nematodes in ca 10.6% of sites containing Meloidogyne. After confirming the identification of 17 isolates of M. javanica and one isolate each of M. incognita, M. arenaria and M. ethiopica by SCAR markers, the populations were used to infer their genetic diversity using RAPD markers. Results revealed low intraspecifc genetic diversity among isolates (13.9%) for M. javanica. Similarly, M. javanica sub-populations (J2a) clustered together (81% of bootstrap), indicating subtle variation from typical J3 populations. The aggressiveness of four populations of M. javanica from different Brazilian states on two susceptible potato cultivars was tested under glasshouse conditions. Results indicated differences in aggressiveness among these populations and showed that potato disease was proportional to nematode reproduction factor. [ABSTRACT FROM AUTHOR]

Summary -- A significant portion of the Cerrado (Brazilian savanna) has been replaced by major crops such as soybean. This may reveal populations of nematodes with different genetic backgrounds compared to cultivated fields. The objectives of this study were to evaluate the genetic variability and aggressiveness of isolates of Meloidogyne spp., contrasting nematodes from preserved areas of the Cerrado with those originating from cultivated soybean fields. Cluster analysis separated isolates of Meloidogyne spp. and isolates from Cerrado and soybean but did not separate an aggressive Meloidogyne morocciensis isolate. The aggressiveness of six selected populations of Meloidogyne spp. from Cerrado and soybean against soybean cultivars was evaluated. Results showed that populations of M. javanica and M. incognita from Cerrado and soybean showed similar aggressiveness. However, for M. morocciensis, the population from soybean was much more aggressive than the one from Cerrado. Aggressiveness is a very intriguing subject that needs special attention for future research in nematology. [ABSTRACT FROM AUTHOR]

A new root-knot nematode parasitising vegetables, flowers and fruits in Brazil, Iran and Chile, is described as Meloidogyne luci n. sp. The female has an oval to squarish perineal pattern with a low to moderately high dorsal arc and without shoulders, similar to M. ethiopica. The female stylet is robust and 15-16 pm long; the distance from the dorsal pharyngeal gland orifice to the stylet base (DGO) is 3-4 p.m. Males have a high, rounded head cap continuous with the body contour. The labial disc is fused with the medial lips to form an elongated lip structure. The head region is not marked by incomplete annulations. Male stylet robust, 20.8-23.0 p.m long with rounded knobs; the DGO is 2.5-4.5 p.m. The stylet of second-stage juveniles (J2) is 12.0-13.5 pm long and the DGO to the stylet base is 2.3-3.3 /xm. The J2 tail is conoid with finely rounded terminus and is 40.0-48.5 //m long. Biochemically, the esterase phenotype L3 (R nv 1.05, 1.10, 1.25) is unique and is the most useful character to differentiate M. luci n. sp. from all other Meloidogyne species. Reproduction is by mitotic parthenogenesis (2rc = 42-46 chromosomes). In a differential host test, the population from Lavandula spica, Caxias do Sul, RS State, Brazil, reproduced on tomato cv. Rutgers, tobacco cv. NC95 and pepper cv. California Wonder. No reproduction occurred on watermelon cv. Charleston Gray, cotton cv. Deltapine 61 or peanut cv. Florunner. In Neighbour-Joining analyses of ITS and D2-D3 rRNA sequences, populations of M. luci n. sp. from Brazil, Chile and Iran clustered together and were clearly separated from other Meloidogyne spp., thus confirming that all three populations are very similar and conspecific. [ABSTRACT FROM AUTHOR]

A root-knot nematode parasitising yakon (Polymia sonchifolia) in São Paulo State, Brazil, is identified as Meloidogyne inornata. The species is redescribed from this material and compared with the original description of M. inornata. The female perineal patterns have a distinct, high, dorsal arch composed of smooth to wavy striae, similar to Meloidogyne incognita. The female stylet is 15.0-17.0 μm long with the cone generally slightly curved dorsally and with well developed knobs. DGO is 3.5-4.5 μm. Males have a high, rounded, head cap that is continuous with the body contour and has a large, round, centrally concave, labial disc raised above the medial lips. The head region is never marked by incomplete annulations and the stylet is robust, 20.0-25.0 μm long, with a straight cone, cylindrical shaft with several small projections and pear-shaped, backwardly sloping knobs. The stylet length of second-stage juveniles is 10.0-13.0 μm, DGO is 2.5-3.5 μm, tail length is 35.0-58.0 μm and c = 6.7-13.9. Biochemically, the esterase phenotype I3 (= Y3) is species-specific and is the most useful character for differentiating M. inornata from other Meloidogyne species. Reproduction is by mitotic parthenogenesis, 3n = 54-58. In a soybean test, cv. Abura was susceptible and cv. LA411219 was highly resistant. As the type material is lost, a neotype female is formally designated. [ABSTRACT FROM AUTHOR]

A root-knot nematode parasitising kiwi fruit (Actinidia deliciosa) in Rio Grande do Sul State, Brazil and grape-vine (Vitis vinifera) in Chile, is identified as Meloidogyne ethiopica Whitehead, 1968. The species is redescribed from this new material and compared with the type description of M. ethiopica and another population of the species from Kenya. The female has an oval to squarish perineal pattern with a moderately high to high dorsal arch, smooth, widely spaced striae, and no 'shoulders'. The head region is set off with an elevated squarish labial disc, usually marked by annulations, and the stylet is 12-15 μm long, the cone usually being slightly curved dorsally and the shaft gradually widening posteriorly to near the junction with the rounded stylet knobs. The DGO is 3.0-5.0 μm behind the knobs. The male has a high, rounded head cap which is continuous with the body contour and has a distinct labial disc, almost circular to hexagonal in shape, and distinctly separated from the medial lips. The stylet is robust, 23-27 μm long with a straight cone and a cylindrical shaft widening slightly near its junction with the basal knobs which are smooth, round to pear-shaped and backwardly sloping. The stylet length of the second-stage juvenile is 11-14 μm, the DGO is 2.0-3.0 μm behind the knobs and the tail length is 52-72 μm. Biochemically, the esterase phenotype E3 ( Ki3) is species-specific and is the most useful character for differentiating M. ethiopica from other species. Reproduction is by mitotic parthenogenesis, 2n 36-38. In a differential host test, populations of M. ethiopica reproduced on tomato, tobacco, pepper and watermelon. No reproduction occurred on cotton or peanut. Using the PCR-RAPD analysis to compare populations from Brazil, Chile and Kenya, a low proportion of polymorphic fragments (about 17.7%) was detected and the isolates clustered together with high bootstrap support (100%), thus confirming that all three populations are very similar and apparently conspecific. [ABSTRACT FROM AUTHOR]

Among plant-parasitic nematodes, root-knot nematodes (RKN), Meloidogyne spp., are the most important parasite infecting economically important crops globally and causing severe losses in crop production. The use of efficient nematode control methods against these parasites depends upon their correct detection in roots and soil samples. Currently, the use of integrated identification methods, including biochemical, molecular, and morphological-based characters, is preferred. But the techniques using morphology and phylogenetic analysis are time-consuming and not suitable for routine analysis. They have only been used for studies of cryptic species, which were identified using integrative taxonomy. Here we describe the enzymatic and molecular-based methods that have successfully been used in Brazil for more than 25 years in the Nematology Lab at Embrapa Genetic Resources and Biotechnology for routine analysis. This technique is a combination of isozyme esterase profiling and molecular markers, with the aim of having a rapid and correct diagnosis of Meloidogyne spp. populations from field and greenhouse., (© 2024. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Meloidogyne graminicola causes significant damage to rice fields worldwide. Sources of resistance to M. graminicola reported in Oryza sativa are limited. Resistance to this species has been found in other Oryza species such as O. glaberrima and O. longistaminata . This study aimed to evaluate the reaction of four wild species of Oryza from the Embrapa Rice and Bean Germplasm Bank (Goiás, Brazil) to a pool of M. graminicola populations and determine the resistance mechanism in O. glumaepatula. Two genotypes of O. glaberrima , one of O. alta , three of O. glumaepatula , one of O. grandiglumis , one of O. longistaminata , and one of O. sativa (control) were included in the study. The results showed that O. glumaepatula was highly resistant (reproduction factor [RF] < 1). O. glaberrima , O. alta , and O. grandiglumis were considered moderately resistant. O. longistaminata was susceptible, although values of RF remained lower than the control O. sativa 'BR-IRGA 410', considered highly susceptible. Histological observations on the interaction of O. glumaepatula and M. graminicola showed reduced penetration of second-stage juveniles (J2s) when this resistant wild accession was compared with O. sativa . An intense hypersensitivity response-like reaction occurred at 2 days after inoculation in the root cortex of the resistant accession. Few J2s established in the central cylinder, and rare collapsed giant cells were observed surrounded by degenerate females. Fluorescence microscopy in O. glumaepatula revealed giant cells and the female body presumably exhibiting accumulation of phenolic compounds. Our study suggests that wild rice accessions, especially from the AA genotype (e.g., O. glumaepatula ), are of great interest for use in future breeding programs with Oryza spp.

Root-knot nematodes (RKN) cause important production losses of rice (Oryza sativa L.) in the world. Together with Meloidogyne graminicola Golden and Birchfield 1965, M. oryzae Maas, Sanders and Dede, 1978 and M. salasi López, 1984 have been causing damages in irrigated rice fields in Central and South America. In addition, six other RKN species may occur in rice fields in other regions of the world. Correct identification of Meloidogyne spp. is difficult but essential for the management of rice RKNs. The objective of this study was to develop some species-specific molecular markers for the diagnosis of South American RKN rice-related species. Isozyme phenotypes indicated the occurrence of some RKN species in the Brazilian samples, namely M. graminicola, M. oryzae, M. javanica, and two cryptic species designated as Meloidogyne sp. 2 and Meloidogyne sp. 3. Random amplified polymorphic DNA (RAPD) analysis of 16 isolates revealed interspecific genetic polymorphism between Meloidogyne spp., but isolates belonging to the same species (i.e., sharing the same esterase phenotype) always clustered together, whatever the species considered. Specific SCAR markers of 230, 120, and 160 bp were developed for M. graminicola, M. oryzae, and M. salasi, respectively. These SCAR markers may be potential molecular tools for application in routine diagnostic procedures subject to their validation with other rice RKN field populations in the world.

RAPD markers were used to characterize the genetic diversity and relationships of root-knot nematodes (RKN) (Meloidogyne spp.) in Brazil. A high level of infraspecific polymorphism was detected in Meloidogyne arenaria, Meloidogyne exigua, and Meloidogyne hapla compared with the other species tested. Phylogenetic analyses showed that M. hapla and M. exigua are more closely related to one another than they are to the other species, and illustrated the early divergence of these meiotically reproducing species from the mitotic ones. To develop a PCR-based assay to specifically identify RKN associated with coffee, three RAPD markers were further transformed into sequence-characterized amplified region (SCAR) markers specific for M. exigua, Meloigogyne incognita and Meloidogyne paranaensis, respectively. After PCR using the SCAR primers, the initial polymorphism was retained as the presence or absence of amplification. Moreover, multiplex PCR using the three pairs of SCAR primers in a single reaction enabled the unambiguous identification of each species, even in mixtures. Therefore, it is concluded that the method developed here has potential for application in routine diagnostic procedures.