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  • Author or Editor: Vanessa S. Mattos x
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Root-knot nematodes negatively impact on coffee yield worldwide. The use of resistant cultivars is the most effective way to manage these pests. The goal of this study was to identify Coffea arabica genotypes with resistance to Meloidogyne paranaensis and M. incognita race 1. Eighteen C. arabica genotypes (EPAMIG’s Germplasm Bank), previously selected for poor host suitability in a M. paranaensis-infested field, plus a resistant and a susceptible standard, were inoculated with these two Meloidogyne species to determine their resistance using nematode reproduction factor (Rf). Accessions for which Rf<1 were considered resistant, while those for which Rf1 were considered moderately resistant or susceptible, also according to statistical analysis. Five accessions from crossing ‘Catuaí Vermelho’ × ‘Amphillo MR 2-161’, one from ‘Catuaí Vermelho’ × ‘Amphillo MR 2-474’, two from ‘Timor Hybrid (UFV 408-01)’ and the standard ‘IPR-100’ were resistant to M. incognita race 1 with Rf<1. Four accessions from ‘Catuaí Vermelho’ × ‘Amphillo MR 2-161’, one from ‘Timor Hybrid (UFV 408-01)’, one from ‘Catuaí Vermelho’ × ‘Amphillo MR 2-474’ and the resistant standard ‘IPR100’ were resistant to M. paranaensis (Rf<1). Field evaluations with parental genotypes showed that plants that originated from progenies ‘Catuaí Vermelho’ × ‘Amphillo MR 2-161’ were resistant to M. paranaensis and also gave a good yield compared to commercial cultivars, showing promising agronomic traits that can be used in breeding programmes to develop new cultivars of C. arabica.

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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.

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Root-knot nematodes (RKN) are important plant pathogens affecting rice in South-East Asia and southern Brazil in irrigated rice fields. In order to investigate the specific diversity of RKN associated with irrigated rice in southern Brazil, Meloidogyne spp. from Rio Grande do Sul (RS) and Santa Catarina (SC) States were characterised biochemically by esterase (Est) and malate dehydrogenase (Mdh) phenotypes. Fifty-six Meloidogyne spp. populations were detected in 48% of rice samples, and a total of five esterase phenotypes were identified, four of which presented as drawn-out bands in different positions. In RS State, M. graminicola (Est VS1), Meloidogyne sp. 2 (Est R2) and Meloidogyne sp. 3 (Est R3) were identified, which corresponded to ca 80, 40 and 10% of samples, respectively. In SC State, M. graminicola, M. javanica (Est J3), Meloidogyne sp. 1 (Est R1), Meloidogyne sp. 2 and Meloidogyne sp. 3 accounted for ca 93.75, 12.50, 62.50, 12.25 and 6.25% of samples, respectively. The esterase phenotypes R1, R2 and R3 are new, never having been detected on rice before. Meloidogyne javanica showed a N1 Mdh phenotype (Rm: 1.0), while four other populations exhibited a N1a (Rm: 1.4) phenotype. All populations were tested with two SCAR markers specific to M. graminicola, which confirmed that, but no specificity was obtained with both markers in relation to the atypical populations analysed. Sequencing and phylogenetic analyses of internal transcribed spacer-rRNA (ITS) were performed to infer the phylogenetic relationship of these atypical Meloidogyne spp. populations. Meloidogyne sp. 1 grouped with the mitotic parthenogenetic species, while the two others (Meloidogyne sp. 2 and sp. 3) clustered with M. graminicola and other meiotic parthenogenetic species. Taken together, these data highlight the unprecedented specific diversity of RKN associated with irrigated rice in southern Brazil. Further morphological and phylogenetic studies involving these atypical isolates will be carried out to identify this complex of species.

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In: Nematology

The type population of Meloidogyne brasiliensis is synonymised under M. ethiopica based on morphological and morphometric similarities, as well as through biochemical, molecular and phylogenetic studies. Meloidogyne ethiopica was first described in 1968 in Tanzania using specimens from a single egg mass culture on tomato and re-described in 2004 using an isolate from Brazil. Meloidogyne brasiliensis was described in 2002 in Brazil based on specimens collected from tomato (type population) and pea. Morphological and morphometric studies of their descriptions showed important similarities in major characters as well as some general variability in others. Characterisation of esterase isozyme phenotypes of three populations of M. ethiopica from Brazil, Chile and Kenya, and two M. brasiliensis populations, resulted in only one esterase pattern (E3), a phenotype already known for M. ethiopica. In PCR assays, the species-specific 350 bp SCAR marker developed for M. ethiopica was amplified from the M. brasiliensis populations tested. In phylogenetic analyses based either on sequences of the ITS1-5.8S-ITS2 and D2-D3 (28S) rRNA regions or on RAPD and AFLP data, the populations of both species clustered together with a strong bootstrap support. Altogether, these results provide congruent evidence that M. brasiliensis is not a valid species but rather a junior synonym of M. ethiopica.

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In: Nematology

In a survey for Meloidogyne spp. in different crops from 11 regions in Ceará State, Brazil, using esterase isozyme electrophoresis as a specific identification method, four atypical populations were characterised from cabbage, papaya, noni and canapum plants, all of which showed an esterase profile different from those previously detected in Brazil. Morphological studies showed typical characteristics of Meloidogyne konaensis. Perineal patterns of females were variable, similar to M. arenaria and M. incognita, stylet length 14-20 μm. In females, the knobs gradually merged with the shaft and the dorsal pharyngeal gland orifice (DGO) ranged from 4 to 7 μm. Although males are not frequently found, the stylet morphology provides the most useful source of diagnostic character for the species, having 6-12 large projections protruding from the shaft. The esterase pattern K3 is unique and species-specific with three major bands Rm 1.0, 1.17, 1.27 and a secondary band Rm 1.10. Some confusion about the true identity of this species was clarified in this study, including differentiation from M. paranaensis. A species-specific SCAR marker developed for M. paranaensis was tested and no amplification products were observed. In Neighbour-Joining analyses of ITS and D2-D3 rRNA sequences, M. konaensis from Brazil appeared clearly separated from M. paranaensis. Pathological tests indicated that coffee is not a host of M. konaensis as previously reported in the original description of this species.

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In: Nematology

Summary

The rice root-knot nematode, Meloidogyne graminicola, has been reported in Southeast Asia, China, India, South Africa, USA, Brazil, and other countries. Recent surveys in Southern Brazil showed that M. graminicola was widespread in irrigated rice in Rio Grande do Sul, Santa Catarina and Paraná states, and the presence of a species complex with a predominance of M. graminicola (Est VS1 = G1) and other variants showing similar esterase phenotypes (Est G2 = R2, G3 = R3). Meloidogyne oryzae (Est O1) and M. ottersoni (Est Ot0) were also part of this complex and were recently re-described and detected on rice. The present study provides an integrative taxonomy approach of the typical and atypical populations of M. graminicola on the basis of morphological, morphometric and molecular data. Considering morphological and morphometric features, the two atypical populations (Est G2 and G3) are in close agreement with the description of M. graminicola. Based on the molecular characterisation, populations G1, G2 and G3 were successfully amplified by M. graminicola SCAR markers, although the specificity of these markers was questioned. Phylogenetic relationships complemented and confirmed the other studies. In maximum likelihood analysis of ITS, D2-D3 rRNA and COXII-16S rRNA sequences, all populations of M. graminicola from different esterase phenotypes clustered together with other M. graminicola populations, thus confirming that these enzyme phenotypes (G1, G2 and G3) are related to the same species. A high level of intraspecific variability was detected among all populations, but no correlation between genetic variability and geographic origins occurred.

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In: Nematology

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.

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In: Nematology

Summary

The type population of Meloidogyne polycephannulata is synonymised with M. incognita based on morphological and morphometric characters, as well as biochemical, molecular and phylogenetic studies. Morphological variability and a wide host range were reported for M. incognita during its first description and later re-description. Meloidogyne polycephannulata was described in Brazil from specimens collected in a carrot field (type population). The esterase phenotype (Est) characterised for this species was identical to the phenotype Est I2 of M. incognita, the most ubiquitous phenotype used for diagnostics. Morphological and morphometric characters of the descriptions of the two nominal species showed major similarities, as well as variability within the range of variation detected in M. incognita. In PCR assays, three SCAR markers species-specific for M. incognita (incK14 F/R, Mi/FR and incB06 F/R) amplified the same fragments of 399 bp, 955 bp and 1200 bp, respectively, for populations in both species. In phylogenetic studies based either on concatenated sequences of ITS1-5.8S-ITS2, D2-D3 rRNA, mitochondrial COII regions or on RAPD and AFLP data, the populations of both species grouped in the same clade with high bootstrap support. Altogether, these results provide congruent evidence that the M. polycephannulata type isolate deposited at the Embrapa Cryopreserved National Collection of Root-knot Nematodes is not a valid species but rather a junior synonym of M. incognita.

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In: Nematology

Summary

Meloidogyne paranaensis is one of the most destructive root-knot nematode species affecting coffee cultivation. This species presents different esterase phenotypes (Est): P1, P2 and P2a, previous studies showing that Est P2 and P2a populations were more aggressive to susceptible coffee cultivars than populations with Est P1, and local producers have even asked if they may be described as other species. The objective of this study was to characterise M. paranaensis populations of different esterase phenotypes (Est P1, P2 and P2a), regarding morphological, morphometric and phylogenetic relationships in distinct regions of ribosomal DNA (rDNA), mitochondrial gene cytochrome c oxidase II (COII) and nuclear protein coding gene HSP90. All populations were identified by esterase phenotype and SCAR-specific markers. Regarding morphology/morphometrics, the three populations were very similar to the description of the species, differing only in the morphology of the male stylet and second-stage juvenile hyaline tail length. Based on the phylogenetic analysis, a low intraspecific variability was detected among M. paranaensis Est P1 and Est P2 populations from Brazil; the Guatemalan population Est P2a, however, showed a genetic differentiation from the Brazilian populations, confirming the geographic genetic distance of this aggressive population. According to this multi-source approach study, in spite of the intraspecific variation, the phylogenetic position of M. paranaensis is absolute, regardless of the enzymatic phenotype and SCAR markers.

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In: Nematology