Search Results (22)

Plant-parasitic nematodes (PPNs) cause big crop losses globally. Safe/reliable methods for their durable management strategies can harness various beneficial relationships among the plant immune system and related microbiomes. Molecular mechanisms basic to these relations reveal wide arrays of significant roles for plant-healthy growth. This review focuses on such relations of microbiomes to prime and immunize plants against PPNs. It also highlights molecular issues facing PPN-resistant varieties with possible solutions such as genetic breeding/engineering, grafting, PPN-antagonistic root exudates, and novel resistant cultivars. These issues call for optimal uses of various widespread groups of microbiomes. Related plant signaling hormones and transcription factors that regulate gene expression and modulate nematode-responsive genes to ease positive/negative adaptation are presented. Exploring PPN-resistance genes, their activation mechanisms, and signaling networks offers a holistic grasp of plant defense related to biotic/abiotic factors. Such factors relevant to systemic acquired resistance (SAR) via plant–microbe interactions to manage PPNs are stressed. The microbiomes can be added as inoculants and/or steering the indigenous rhizosphere ones. Consequently, SAR is mediated by the accumulation of salicylic acid and the subsequent expression of pathogenesis-related genes. To activate SAR, adequate priming and induction of plant defense against PPNs would rely on closely linked factors. They mainly include the engaged microbiome species/strains, plant genotypes, existing fauna/flora, compatibility with other involved biologicals, and methods/rates of the inoculants. To operationalize improved plant resistance and the microbiome’s usage, novel actionable insights for research and field applications are necessary. Synthesis of adequate screening techniques in plant breeding would better use multiple parameters (molecular and classical ones)-based ratings for PPN-host suitability designation. Sound statistical analyses and interpretation approaches can better identify genotypes with high-level, stable resistance to PPNs than the commonly used ones. Linking molecular mechanisms to consistent field relevance can be progressed via dissemination of many advanced techniques. The CRISPR/Cas9 system has been effective in knocking out both the OsHPP04 gene in rice to confer resistance against Meloidogyne graminicola and the GhiMLO3 gene in cotton to minimize the Rotylenchulus reniformis reproduction. Its genetic modifications in crops synthesized “transgene-free” PPN-resistant plants without decreased growth/yield. Characterizing microbiome species/strains needed to prime and immunize plants requires better molecular tools for fine-scale taxonomic resolution than the common ones used. The former can distinguish closely related ones that exhibit divergent phenotypes for key attributes like stability and production of enzymes and secondary metabolites. As PPN-control strategies via tritrophic interactions are more sensitive to the relevant settings than chemical nematicides, it is suggested herein to test these settings on a case-by-case basis to avoid erratic/contradictory results. Moreover, expanding the use of automated systems to expedite detection/count processes of PPN and related microbes with objectivity/accuracy is discussed. When PPNs and their related microbial distribution patterns were modeled, more aspects of their field distributions were discovered in order to optimize their integrated management. Hence, the feasibility of site-specific microbiome application in PPN–hotspot infections can be evaluated. The main technical challenges and controversies in the field are also addressed herein. Their conceptual revision based on harnessing novel techniques/tools is direly needed for future clear trends. This review also engages raising growers’ awareness to leverage such strategies for enhancing plant resistance and advancing the microbiome role. Microbiomes enjoy wide spectrum efficacy, low fitness cost, and inheritance to next generations in durable agriculture. Full article

The growing demand for sustainable and cost-effective alternatives to synthetic nematicides has driven interest in naturally derived compounds with selective activity against plant-parasitic nematodes. In this study, we evaluated the bionematicidal potential of undecanoic acid, a naturally occurring medium-chain (C11) fatty acid, against two economically important root-knot nematodes: Meloidogyne ethiopica and M. graminicola. Direct contact bioassays demonstrated 100% mortality of both species within 24 h of exposure to a 1 mg/mL concentration, confirming strong and rapid nematicidal activity. In contrast, exposure of a non-target, the free-living soil nematode Cephalobus sp., resulted in only ca. 20% mortality, suggesting a favorable degree of selectivity toward phytoparasites. Additionally, environmental fate modeling indicated a predicted distribution of this compound of ca. 69% in soil, 28% in water, and 3% in air environmental compartments, consistent with its use as a soil-applied agent, while highlighting the need for environmental risk assessment under field conditions. As a naturally sourced compound, undecanoic acid offers advantages over synthetic nematicides, not only due to its biodegradability and potential reduced environmental impact, but also its lower cost compared to commercial pesticide active ingredients. The selective toxicity of undecanoic acid makes it a favorable candidate for integrated pest management programs, particularly in low-input or organic systems. These results underscore the potential of this naturally occurring fatty acid as an effective and sustainable tool for nematode control. Further studies on formulation optimization, persistence, and field efficacy will be needed to fully realize its application in agricultural systems. Full article

Plant-parasitic nematodes (PPNs) pose a significant threat to agricultural production and global food security. To mitigate this challenge, quantitative trait locus (QTL) mapping and genome-wide association studies (GWAS) have been extensively employed in crop resistance breeding research. These methods have identified resistance-related genes and genetic markers, offering a solid scientific basis and practical tools for resistance breeding. This review summarizes recent advances in QTL and GWAS applications for enhancing resistance to cyst nematodes (Heterodera glycines, H. filipjevi, and H. avenae), root-knot nematodes (Meloidogyne graminicola and M. incognita), and root-lesion nematodes (Pratylenchus spp.). It also evaluates the commercial deployment of resistance genes, discusses integrated breeding strategies, and highlights future research directions toward developing durable nematode-resistant crops. Full article

To identify the root-knot nematodes (RKNs) infecting onions in Yuanmou County, Yunnan Province, morphological and molecular biological techniques were used. Observation of their life cycle and pathogenicity was conducted through artificial inoculation experiments in a greenhouse. The results show that the morphological characteristics and measurement data of the second-stage juveniles (J2s) and females of RKNs infecting onion roots are highly consistent with those of Meloidogyne graminicola (M. graminicola). Sequence alignment of the mitochondrial DNA (mtDNA) COXI region and 28S rDNA D2-D3 region revealed sequence similarities of 99.51–100.00% and 99.48–99.61%, respectively, compared with M. graminicola sequences from GenBank. The specific primers Mg-F3/Mg-R2 reliably amplified a characteristic 369 bp band. Inoculation experiments confirmed that the pathogen can complete its entire life cycle (approximately 26 days (ds)) on the roots of healthy onion seedlings, inducing typical root-knot symptoms and females. In conclusion, the pathogen was identified as M. graminicola, which is the first report of M. graminicola infecting onions in China. This study provides important theoretical support for the molecular diagnosis of onion root-knot nematode disease and the green control of Allium L. vegetables in China. Full article

Meloidogyne graminicola represents a significant pathogen of rice, with considerable variability in nematode resistance observed across rice germplasms. However, the gene regulatory networks and molecular mechanisms underlying the differential responses of resistant and susceptible cultivars to M. graminicola infection remain poorly understood. To identify potential sources of resistance, 122 indica cultivars were screened under controlled conditions based on gall formation in infected roots. Notably, Indian indica accession 685 exhibited exceptional resistance, characterized by complete suppression of nematode development within root tissue. To investigate the molecular responses of rice cultivars to M. graminicola infection, RNA sequencing was conducted to analyze gene expression profiles at 5 days post-inoculation (dpi) in resistant cultivar 685, moderately susceptible cultivar 1008, and susceptible cultivar 9311. Subsequent differential gene expression analysis and weighted gene co-expression network analysis (WGCNA) identified key biological pathways, including sugar metabolism, autophagic degradation, and phytohormone signal transduction. Additionally, candidate hub genes were identified and validated through RT-qPCR. This study offers new insights into rice–M. graminicola interactions, highlighting critical molecular factors involved in resistance and susceptibility in host plants. Full article

The pine wood nematode (Bursaphelenchus xylophilus), the pathogen of pine wilt disease (PWD), has caused enormous economic losses in Asian forests. Whether venom allergen proteins (VAPs) are involved in the accumulation of key defense substances in pine trees during the interaction between B. xylophilus and host trees, and their specific function as putative effectors secreted through stylets, has not been fully elucidated. In this study, the role of the BxVAP2 effector protein in the infection process was analyzed through bioinformatics and phylogenetic tree construction. The expression profile of BxVAP2 during infection was analyzed using qRT-PCR, and its expression under the stress of Pinus massoniana metabolites was examined. Toxicity assays were conducted through the Agrobacterium transient expression of BxVAP2 in Nicotiana benthamiana, and its subcellular localization was investigated. The results showed that BxVAP2 contains a CAP domain and shares close evolutionary relationships with venom allergen proteins from related species, such as Bursaphelenchus mucronatus, Aphelenchoides besseyi, Aphelenchoides fujianensis, and Meloidogyne graminicola. BxVAP2 was upregulated during the infection of P. massoniana, indicating that BxVAP2 is a key effector in the infection and colonization process of B. xylophilus and may play an important role during the rapid population growth phase. BxVAP2 responds to P. massoniana metabolites, where different concentrations of α-pinene suppressed its expression, while high concentrations of β-pinene promoted its expression. Subcellular localization revealed that BxVAP2 localizes to the cell membrane and nucleus. The transient expression of BxVAP2 in N. benthamiana induced programmed cell death and regulated pattern-triggered immunity marker genes. These findings suggest that BxVAP2 plays an important role in the interaction between B. xylophilus and its host, responding to terpene stress and triggering plant defense. Full article

Direct-seeded rice (DSR) is gaining popularity among farmers due to its environmentally safe and resource-efficient production system. However, managing the rice root-knot nematode (RRKN), Meloidogyne graminicola, remains a major challenge in DSR cultivation. Developing genetic resistance is a pragmatic and effective approach compared to using hazardous pesticides. Pusa Basmati 1121 (PB1121) is the most popular Basmati rice variety, but it is highly susceptible to RRKN. In contrast, Phule Radha (PR) has shown highly resistant reaction to RRKN, as reported in our earlier study. We generated an F_2:3 population from the cross of PB1121/PR and evaluated it for RRKN resistance-related traits under artificial inoculation conditions. The distribution pattern of traits in the F_2:3 population indicated that resistance may be governed by a few major-effect genes and many minor-effect genes. The molecular markers reported to be associated with QTLs governing RRKN resistance traits were used to test in the current population. Although the simple linear regression identified significant associations between the markers and RRKN resistance-associated traits, these associations were spurious as the LOD score was below the threshold limit. This indicates that PR possesses novel genomic regions for resistance to RRKN as it does not possess any of the earlier reported QTLs. Full article

The rice root-knot nematode (RRKN), Meloidogyne graminicola Golden and Birchfield 1965, is a dangerous crop pest that affects rice production on a global scale. The largest rice-producing countries struggle with the impacts of RRKN infestation, namely, underdeveloped plants and a reduction in rice grain that can reach up to 70% of crop yield. In addition, the shift to strategies of sustainable pest management is leading to a withdrawal of some of the most effective pesticides, given the dangers they pose to the environment and human health. Volatile metabolites produced by plants can offer safer alternatives. The present study characterized the nematicidal activity of volatile phytochemicals against the RRKN and compared the most active with commercial nematicides concerning their safety to the environment and human health. Rice plants were used to grow large numbers of RRKNs for direct-contact bioassays. Mortality induced by the volatiles was followed for four days on RRKN second-stage juveniles. Of the 18 volatiles tested, carvacrol, eugenol, geraniol, and methyl salicylate showed the highest mortalities (100%) and were compared to traditional nematicides using (eco)toxicological parameters reported on freely available databases. While methyl salicylate had a faster activity, carvacrol had more lasting effects. When compared to synthetic nematicides, these volatile phytochemicals were reported to have higher thresholds of toxicity and beneficial ecotoxicological parameters. Ultimately, finding safer alternatives to traditional pesticides can lower the use of damaging chemicals in farming and leverage the transition to agricultural practices with a lower impact on biodiversity. Full article

Meloidogyne graminicola (Mg), commonly referred to as rice root-knot nematodes (RKNs), is one of the most prevalent plant parasitic nematodes in rice agroecosystems, and sustainable agricultural practices are still limited. This study aimed to assess the effectiveness of soil microbiotas extracted from different agricultural practices in reducing RKN damage to rice plants. We used conservation agriculture (CA), cover crops with machine tillage (CA), conservation agriculture without tillage (CAU), and conventional agriculture practices (CT). All types of soil microbiotas were isolated from soil samples collected from each rice agricultural practice in the Preah Vihear and Kampong Thom provinces of Cambodia in order to test the effectiveness of the microbiotas against Mg on rice plants (Variety IR64). The experiment was conducted in test tubes, using sterilized sand to grow rice. Then, 250 juveniles (J2) were used to infect each tube and were classified into three treatments: (1) infected 25 mL of microbiota suspensions from non-sterilized soil (M); (2) infected 25 mL of microbiota from sterilized soil (ST); and (3) a control with only J2 (CT). After 3 weeks of infection, rice plants were examined under microscopes to measure the number of nematodes (J2 and eggs). The results showed that the number of nematodes was significantly different under treatment (ST) 230 ± 100.132 compared to treatment (M) 159 ± 64.41, respectively. The data demonstrated that soil microbiotas in CA were effective in reducing Mg damage to rice roots, a method which can be used as a biological control to lower RKN in rice plants. However, further research is required to conduct the assessment of the effects of microbiotas on rice development and yield and determine the taxa of beneficial microbiomes with the most benefit to rice growth. Full article

Rice (Oryza sativa L.) is one of the most widely grown crops in the world, and is a staple food for more than half of the global total population. Root-knot nematodes (RKNs), Meloidogyne spp., and especially M. graminicola, seem to be significant rice pests, which makes them the most economically important plant-parasitic nematode in this crop. RKNs develop a feeding site in galls by causing host cells to differentiate into hypertrophied, multinucleate, metabolically active cells known as giant cells. This grazing framework gives the nematode a constant food source, permitting it to develop into a fecund female and complete its life cycle inside the host root. M. graminicola effector proteins involved in nematode parasitism, including pioneer genes, were functionally characterized in earlier studies. Molecular modelling and docking studies were performed on Meloidogyne graminicola protein targets, such as β-1,4-endoglucanase, pectate lyase, phospholipase B-like protein, and G protein-coupled receptor kinase, to understand the binding affinity of Beta-D-Galacturonic Acid, 2,6,10,15,19,23-hexamethyltetracosane, (2S)-2-amino-3-phenylpropanoic acid, and 4-O-Beta-D-Galactopyranosyl-Alpha-D-Glucopyranose against ligand molecules of rice. This study discovered important molecular aspects of plant–nematode interaction and candidate effector proteins that were regulated by M. graminicola-infected rice plants. To the best of our knowledge, this is the first study to describe M. graminicola’s molecular adaptation to host parasitism. Full article

Meloidogyne graminicola is a destructive soil-borne pathogen that causes rice yield losses (Oryza sativa L.) in tropical and subtropical areas. This study investigated the effect of M. graminicola population densities on plant height, heading, and the photosynthetic parameters of rice in a greenhouse. Two-week-old rice plants were inoculated with different M. graminicola densities (250, 500, 750, 1000, 1500, and 2000 J2s/plant) and observations were recorded at 30, 60, and 90 days after inoculation (DAI). Reductions in growth and photosynthetic parameters caused by M. graminicola densities were calculated in relation to a control (non-inoculated rice). Results revealed that M. graminicola infection with low population densities (0–500 J2s/plant) did not influence the rice plant height during 30–60 DAI, but significantly lowered the plant height, panicle growth rate, and panicle length of rice at 90 DAI. The chlorophyll content of rice inoculated with 500–2000 J2s was significantly lower than that of the control. Furthermore, M. graminicola infection with 500 J2s/plant significantly lowered the transpiration rate and net photosynthetic rate by 21.21% and 21.81%, respectively, compared with the control (p < 0.05). M. graminicola with a low population density significantly reduced the net photosynthetic rate of rice, which affected organic matter accumulation, resulting in growth retardation and lower yields (p < 0.05). Full article

Rice (Oryza sativa L.) is one of the main cultivated crops worldwide and represents a staple food for more than half of the world population. Root-knot nematodes (RKNs), Meloidogyne spp., and particularly M. graminicola, are serious pests of rice, being, probably, the most economically important plant-parasitic nematode in this crop. M. graminicola is an obligate sedentary endoparasite adapted to flooded conditions. Until recently, M. graminicola was present mainly in irrigated rice fields in Asia, parts of the Americas, and South Africa. However, in July 2016, it was found in northern Italy in the Piedmont region and in May 2018 in the Lombardy region in the province of Pavia. Following the first detection in the EPPO region, this pest was included in the EPPO Alert List as its wide host range and ability to survive during long periods in environments with low oxygen content, represent a threat for rice production in the European Union. Considering the impact of this nematode on agriculture, a literature review focusing on M. graminicola distribution, biology, identification, and management was conducted. Full article

Meloidogyne spp., commonly known as root-knot nematodes (RKN), are among the most economically damaging plant-parasitic nematodes to horticultural and field crops, mainly due to their pathogenic effect, worldwide distribution, and wide host range. RKN pest management relies on the use of commercial synthetic pesticides, such as broad-spectrum fumigants and nervous system toxins, which kill or disrupt the feeding or reproductive behavior of nematodes. These active chemicals can cause negative environmental and public health impacts and are feared to lead to resistance and immunity. As a sustainable alternative, the use of essential oils (EOs) as nematicides has shown great promise. These natural products are mostly biodegradable and subjected to less strict regulatory approval mechanisms for their exploration. The present work reviews the existing bibliography on the direct biological activity of EOs against RKNs. A total of 49 publications from 1995 to 2020 were identified to have reported on the anti-RKN activity of EOs. Plants from the Lamiaceae and Compositae families make up more than 50% of the source material for EO extraction. The highest activities were reported for EOs of the Monarda, Artemisia, Filipendula, and Satureja genus. These taxa show potential that can be further explored for highly active anti-RKN phytochemicals with practical applications in sustainable pest management strategies. Full article

Meloidogyne graminicola is one of the most harmful organisms in rice cultivation throughout the world. This pest was detected for the first time in mainland Europe (Northern Italy) in 2016 and was subsequently added to the EPPO Alert List. To date, few methods are available for the control of M. graminicola and new solutions are required. In 2019, field trials using rice plants as trap crops were performed in a Lombardy region rice field where five plots for three different management approaches were staked out: (i) Uncultivated; (ii) Treated: three separate cycles of rice production where plants were sown and destroyed each time at the second leaf stage; (iii) Control: rice was sown and left to grow until the end of the three cycles in treated plots. The results showed that in the treated plots, the nematode density and the root gall index were lower than for the other two management approaches. Moreover, the plant population density and rice plant growth were higher than the uncultivated and control plots. In conclusion, the use of the trap crop technique for the control of M. graminicola gave good results and thus it could be a new phytosanitary measure to control this pest in rice crop areas. Full article

Protein disulfide isomerase (PDI) is a multifunctional enzyme that catalyzes rate-limiting reactions such as disulfide bond formation, isomerization, and reduction. There is some evidence that indicates that PDI is also involved in host-pathogen interactions in plants. In this study, we show that the rice root-knot nematode, Meloidogyne graminicola, has evolved a secreted effector, MgPDI2, which is expressed in the subventral esophageal glands and up-regulated during the early parasitic stage of M. graminicola. Purified recombinant MgPDI2 functions as an insulin disulfide reductase and protects plasmid DNA from nicking. As an effector, MgPDI2 contributes to nematode parasitism. Silencing of MgPDI2 by RNA interference in the pre-parasitic second-stage juveniles (J2s) reduced M. graminicola multiplication and also increased M. graminicola mortality under H₂O₂ stress. In addition, an Agrobacterium-mediated transient expression assay found that MgPDI2 caused noticeable cell death in Nicotiana benthamiana. An intact C-terminal region containing the first catalytic domain (a) with an active motif (Cys-Gly-His-Cys, CGHC) and the two non-active domains (b and b′) is required for cell death induction in N. benthamiana. This research may provide a promising target for the development of new strategies to combat M. graminicola infections. Full article