First report of guava root-knot nematode (Meloidogyne enterolobii) infecting gardenia in Brazil

<i>Meloidogyne chitwoodi</i> and <i>Meloidogyne fallax</i>

The root-knot nematode (RKN) Meloidogyne mayaguensis is considered as one of the most damaging RKN species because of its extremely wide host range. Recent surveys have shown the rapid spread of this parasite in agro-ecosytems, often making crop cultivation not viable in the heavily infested areas. Here, we report the identification, molecular cloning, genomic organisation and sequence analysis of a new satellite DNA (satDNA) family from M. mayaguensis (named pMmPet). It is comprised of two groups of A+T rich, tandemly repeated units of 174 and 180 bp, respectively. Using these sequences as targets, hybridisation and PCR experiments performed on a wide collection of 44 populations belonging to 15 RKN species showed that the pMmPet family could only be detected in the 16 M. mayaguensis populations tested. In addition, because of their repetitive nature, positive detection of pMmPet sequences was achieved in single individual nematodes. Therefore, the repeated sequence described here possesses features that make it an excellent candidate for use as a specific and extremely sensitive tool for the accurate detection and identification of this invasive pest on a routine basis. Clearly, monitoring the occurrence and spread of M. mayaguensis at the domestic and international levels are needed to avoid wholesale loss of agricultural resources in the infested regions.

The aim of this study was to examine the effects of amendments with leaf biomass on the development of tomato plants in a soil where root-knot nematodes (Meloidogyne mayaguensis) and/or a nematophagous fungus (Arthrobotrys oligospora, strain ORS 18697) had been inoculated. Six origins of leaf biomass were chosen: Acacia mangium, Acacia holosericea, Eucalyptus camaldulensis, Casuarina equisetifolia, Azadirachta indica and Sorghum vulgare. These leaf biomass types inhibited the development of the aerial parts of the tomato plants. This negative effect was not observed when the fungus was inoculated. On the contrary, plant growth was stimulated. Moreover, the antagonistic activity of Arthrobotrys oligospora was strengthened in the presence of ground leaf powder, especially that from Acacia holosericea. The effects of phenolic compounds on fungal growth and predatory activity and on plant growth are discussed.

One of the modes of action of endophytic fungi against plant pathogens e.g. plant parasitic nematode, is the production of toxic culture filtrate. Experiments were conducted to investigate the antagonistic effects of different concentrations of the culture filtrate produced by the endophytic fungi Nigrospora sp. isolate RS 10 against the root knot nematode Meloidogyne spp. Nigrospora sp. isolate RS 10 was isolated from the healthy root of a sengon plant ( Paraserianthes falcataria ). Three different concentrations of the culture filtrate were investigated using in vitro bioassays against the motile juvenile stage 2 of the root knot nematode Meloidogyne spp. Inactivation and mortality were recorded after 1, 3 and 24 hrs of exposure to culture filtrates. The mortality of the root-knot nematode Meloidogyne -J2 after 24 hrs exposure to the culture filtrate was confirmed by rinsing with sterile distilled water that demonstrated the effects of the culture filtrate treatment were irreversible, as nematodes did not recover. Nematode mortality rates after 1 to 24 hr exposure periods ranged from 80 % to 100 %. The effects of the culture filtrates on root-knot nematode Meloidogyne -J2 increased with increasing culture filtrate concentration.

Melon (Cucumis melo L.) is a vegetable of high economic importance in Brazil, with an average annual production of 862,387 tons (IBGE 2023). However, phytosanitary problems associated with soilborne pathogens have limited the productive potential of this crop. In October 2024, plants with stunted growth, yellowed leaves, and wilting symptoms during the hottest periods of the day were observed in commercial yellow melon production areas located in Ribeira do Amparo, Bahia (11°02'18.7"S 38°25'51.4"W). Complete plant mortality was recorded in a 2-hectare area fifty days after planting. Galls and egg masses, typical symptoms of root-knot nematode (Meloidogyne spp.) infection, were observed on the roots. Egg masses were collected and inoculated, one mass per plant of tomato cv. Santa Cruz Kada Gigante, for the purpose of obtaining a pure culture, identification, and pathogenicity tests. Morphological characterization was determined using perineal region cuts on females, revealing typical characteristics of Meloidogyne enterolobii, including an oval shape and a moderately high dorsal arch with smooth ventral striations. For molecular characterization, genomic DNA (n = 50) was extracted from females using Worm Lysis Buffer (WLB), as described by Carvalho et al. (2019). Molecular identification was performed by PCR using species-specific primers for Meloidogyne enterolobii (Long et al. 2006). Amplification of a 256 bp fragment was observed and visualized under UV light using a transilluminator (Major Science). The amplified product was subjected to Sanger sequencing (ABI 3500, Applied Biosystems). The obtained sequence was aligned in Geneious Prime version 2024.1 (Biomatters Ltd.) and compared with the GenBank database, showing 99% similarity to Meloidogyne enterolobii (accession number PV929444). To fulfill Koch’s postulates, an experiment was conducted with yellow melon (Cucumis melo var. inodorus) under greenhouse conditions. Fifteen-day-old seedlings were transplanted into 7 L pots containing autoclaved soil, sand, and substrate in a 1:1:1 ratio. Nematode extraction was performed according to the methodology described by Coolen and D’Herde (1972). Subsequently, 2,000 J2 were inoculated per pot, and the plants were maintained for 60 days. The inoculated plants exhibited characteristic symptoms similar to those observed under field conditions, whereas the control plants remained asymptomatic. According to the methodology of Oostenbrink (1966), the final J2 population was quantified by counting in a Peters chamber under a light microscope, resulting in a reproduction factor (final population/initial population) of 10.1. To the best of our knowledge, this is the first report of Meloidogyne enterolobii on melon plants in Brazil, highlighting the need for management strategies to reduce the pathogen's impact on crop production.

Plant-parasitic nematodes are one of the main biotic factors limiting agricultural production worldwide, with root-knot nematodes (Meloidogyne spp.) being the most damaging group. This study was conducted to evaluate the efficacy of soil microbiomes, associated with various subtropical fruit trees, on the management of a Meloidogyne enterolobii population. Of 14 soil microbiomes tested for nematode suppression, 9 samples in the first experiment and 10 samples in the repeat experiment had significantly (p ≤ 0.05) lower numbers of eggs and J2 compared to the untreated control. The highest nematode suppression was recorded for SA12 extracted from a papaya orchard with a 38% reduction in the nematode population density. In addition, the presence of some bacteria (Bacillus aryabhattai, B. funiculus and B. simplex) and fungi (Metarhizium marquandii, Acremonium sp. and Mortierella sp.) was correlated to a higher suppression potential in some samples. Substantial variations were observed for the diversity of bacterial and fungal isolates among the samples collected from various crop hosts and regions. This suggests that the nematode suppression potential of different soil microbiomes highly depends on the abundance and diversity of fungal and bacterial strains present in the soil. The study confirmed that among all variables, soil dryness, pH, Fe, Zn, organic matter, altitude, and crop cultivar strongly influenced the soil microbial composition.

Samples of galled roots, resembling those induced by root-knot nematodes, and rhizosphere soil were collected from potted plants of Ulmus parvifolia cvs. Allee and Drake in Lake County, Florida. Nematode species were identified using both molecular analysis and morphology of perineal patterns. Meloidogyne enterolobii and M. javanica were identified from U. parvifolia cv. Allee. Meloidogyne arenaria and M. javanica were identified from U. parvifolia cv. Drake. This is a first report of these nematode species infecting Chinese Elm in Florida.

One of the main problems faced by guava production is the decline caused by the root-knot nematode (Meloidogyne enterolobii), which has a wide distribution in Brazil. This study aimed to evaluate the productive and morphological compatibility and variability of guava accessions grafted on BRS Guaraçá, a rootstock with resistance to the root-knot nematode. The experiment was conducted with 83 accessions from the Psidium Germplasm Bank (Petrolina, Pernambuco State, Brazil). The evaluated traits were stem diameter, canopy diameter I and II, plant height, total number of fruits, total fruit weight, mean fruit weight, seed weight, pulp weight, fruit width and length. Except for the stem diameter ratio, all variables showed significant diferences (p &lt; 0.05), indicating phenotypic variability. The evaluated accessions showed no incompatibility symptoms, e.g., cracks, exudations and diferences for stem diameter in the grafted area, indicating high compatibility. The accessions formed vigorous plants in the second harvest cycle, with mean canopy diameter of 2.3 m and mean plant height of 2.2 m, also indicating high compatibility. The accessions Gua64BA, Gua181ES, Gua06MA, Pedro Sato and Gua99AM showed the highest values for pulp and fruit weight (around 160 g), whereas Gua96AM, Gua70RO, Gua192ES, Gua01MA and Gua183ES showed the highest fruit production values (around 20 kg plant−1), being recommended for grafting in BRS Guaraçá or as potential parents for population development.

Root-knot nematodes (RKNs; Meloidogyne spp.) are a major constraint of pepper (Capsicum annuum L.) crops worldwide. In Mexico, Sinaloa State is one of the main producers of pepper; however, there is little information available on the distribution, prevalence, and incidence of RKN on this crop. Identification of RKN species and estimation of the epidemiological factors are important to design its management strategies. A total of 190 RKN samples from Los Mochis, Culiacan, La Cruz, and Escuinapa areas of Sinaloa were collected from pepper plants at production stage under greenhouse conditions, to analyze the distribution, prevalence, and incidence of RKN. Primary identification of RKN species was based on perineal pattern morphology and confirmed by molecular SCAR marker–based identification. RKNs were found in all the surveyed greenhouses of pepper, confirming their absolute distribution and prevalence in this crop. Meloidogyne enterolobii, Meloidogyne incognita, and Meloidogyne javanica were identified in the four areas. Overall incidence of M. enterolobii, M. incognita, M. javanica, and mix of M. enterolobii + M. incognita was 63.7, 11.7, 12.8, and 11.7%, respectively, indicating that RKNs are a serious threat for pepper and other crops in Sinaloa State. This information will enable pepper growers to design and implement an appropriate control for RKN species.

IN VITRO EFFECT OF Purpureocillium lilacinum (Thom) Luangsa-Ard et al. AND Pochonia chlamydosporia var. catenulata (Kamyschko ex Barron &amp; Onions) Zare &amp; Gams ON THE ROOT-KNOT NEMATODES [P. chlamydosporia (Kofoid &amp; White) Chitwood AND Meloidogy nemayaguensis Rammh &amp; Hirschmann]&#x0D; Purpureocillium lilacinum strain PL-11 and Pochonia chlamydosporia strain JL-1 fungal strains, are a biological alternative to reduce plant parasitic nematodes on the roots of plants. The objective of this research was to determine the most effective concentration of P. lilacinum strain PL-11 and P. chlamydosporia strain JL-1, for the management of root-knot nematode (Meloidogyne spp.). In the Plant Pathology laboratory, at University of Caldas, in a completely randomized design, 1 mL of P. lilacinum (1 x 109 spores / mL) were added to 32 bacteriological Petri dishes with agar; subsequently, 16 of them were inoculated with a 30 mL suspension containing 10 eggs of P. chlamydosporia and Meloidogyne mayaguensis and, the other 16, were inoculated with a 30 mL suspension containing 10 juveniles (J2) of the two Meloidogyne species. Fungal infection of eggs and mortality of juveniles (J2) of the two species of Meloidogyne were evaluated at 24, 72, 120 and 168 h. The same procedure was performed with P. chlamydosporia, the combination P. lilacinum and P. chlamydosporia, P. lilacinum and P. chlamydosporia in combination with Carbofuran at concentrations between 1 x 103 and 1 x 109 spores / mL. The positive and negative controls were Carbofuran and water, respectively. Results demonstrated that mixing P. lilacinum and P. chlamydosporia (1 x 106 spores / L) in combination with Carbofuran, and the mixture P. lilacinum and P. chlamydosporia (1 x 108 spores / mL), caused the highest infections on eggs with 85% and 80%, respectively, and caused the highest mortality of juvenile (J2) of M. incognita and M. mayaguensis with 93% and 75%, respectively, compared to the water treated group, at 168 h.

Potential resistance to the root-knot nematode (RKN) Meloidogyne enterolobii in 72 Glycine soja and 44 G. max soybean genotypes was evaluated in greenhouse experiments. Approximately 2,500 eggs of M. enterolobii were inoculated on each soybean genotype grown in a steam sterilized 1:1 sand to soil mixture. Sixty days postinoculation, plants were destructively harvested to determine the host status. The host status of each soybean genotype was determined by assessing root galling severity and calculating the final eggs per root system divided by the initial inoculum, or the reproduction factor (Rf). Five G. soja soybean genotypes were identified as resistant (Rf < 1) to M. enterolobii: '407202', '407239', '424083', '507618', and '639621'. None of the tested G. max soybean genotypes were identified as resistant to M. enterolobii. Some of the G. max genotypes determined to be susceptible to M. enterolobii include 'Hagood', 'Avery', 'Rhodes', 'Santee', and 'Bryan'. The genotype 'Bryan' had the lowest Rf values among the group at 5.06 and 6.67 in two independent trials, respectively, which represents a five- to sixfold increase in reproduction of M. enterolobii. Plant genotypes resistant to RKNs are effective in managing the disease and preserving yield, cost-efficient, and environmentally sustainable, and host resistance is often regarded as the most robust management tactic for controlling plant-parasitic nematodes. Resistance to RKNs in soybean genotypes has been identified for other Meloidogyne species, yet there is currently limited data regarding soybean host status to the highly aggressive nematode M. enterolobii. This study adds to the knowledge of potential native resistance to M. enterolobii in wild and cultivated soybean.

Root-knot nematodes (Meloidogyne spp.) cause great economic impact in the sector of agriculture while the number of existing commercial nematicides has been drastically reduced. The metal-based nanoparticles offer new possibilities as agrochemicals. In the current study, we shed light on the role of copper/iron based nanoparticles as bioactive agents against the root knot nematode Meloidogyne spp; along with the plant enhancement properties on the nematode infested host. Same sized PEGylated Cu, CuFe and CuFeO2 NPs, were solvothermally synthesized characterized and evaluated against M. incognita and M. javanica nematodes, in terms of paralysis and biological cycle arrest in tomato plants. Comparisons were made against the commercial nematicide fosthiazate. All the tested compositions revealed nematicidal activity, but CuFe NPs were found best effective exhibiting the lowest EC50 value calculated at 0.03 μg ai g/soil. Additionally, a fresh shoot and root weight increase was evident in tomato plants treated with CuFe NPs.

Tepary bean (Phaseolus acutifolius A. Gray) is a drought tolerant leguminous crop and due to its multi-purpose use, it can easily be incorporated into different production systems. It being an undertilised crop, its production is usually relegated to poor sandy soils that are highly prone to root-knot nematodes (Meloidogyne species). Commonly communal producers of tepary beans use retained seeds with no knowledge of the nematode resistance status of the seeds. Hence the objective of the study was to determine whether Meloidogyne enterolobii will be able to reproduce on the Kickapoo white tepary bean and cause a reduction in the plant's growth variables. To achieve this objective, Kickapoo white tepary bean seedlings were exposed to 0, 25, 50, 125, 250, 625, 1250 and 3125 M. enterolobii eggs and second-stage juveniles (J2) in 2021 and validated in 2022 under shade-net conditions. At 56 days after inoculation, plant and nematode variables were collected and reproductive factor (Rf) was computed. Plant growth variables were not reduced whereas, nematode variables increased with an increase in nematode levels. In both experiments the Rf values were above a unity for all inoculation levels, indicating that nematodes were able to reproduce.. In conclusion, Kickapoo white tepary bean is tolerant to M. enterolobii.

Globally, the guava root-knot nematode (Meloidogyne enterolobii) is becoming an emerging threat of note in crops with or without Mi resistance genes. Watermelon (Citrullus lanatus) cultivars are highly susceptible to Meloidogyne species, with all cultivars without genotypes with resistance to the genus. In contrast, nematode management options for watermelon production had since the withdrawal of fumigant nematicides been constrained. The objective of this study was to investigate the comparative efficacy of the locally-developed cucurbitacin phytonematicides and commercially available synthetic chemical nematicide Velum on growth and fruit yield and quality of watermelon cv. ‘Congo’, along with its accumulation of foliar nutrient elements and suppression of M. enterolobii population densities under field conditions. Nemarioc-AL and Nemafric-BL phytonematicides were each applied biweekly at 2% per seedling using 500 ml solution, while Velum was applied once using 500 ml solution at 0.08 ml/15 L chlorine-free water. At 90 days after the treatments, relative to untreated control, the two phytonematicides and Velum (a.i. fluopyram) significantly increased plant growth, fruit yield and quality, although with the accumulation of phosphorus in leaf tissues, with efficacies of the three products being comparable. Similarly, relative to untreated control, the three products significantly reduced nematode eggs and juveniles in roots and juveniles in soil, with efficacies that were significantly comparable. In conclusion, the benefits of phytonematicides on the productivity of watermelon cv. ‘Congo’ and suppression of population densities of M. enterolobii were comparable.

Evaluation of summer cover crops for host suitability of Meloidogyne enterolobii