Rice Root Knot Research Articles

Prevalence and Distribution of Rice Root Knot Nematode in Rice Nurseries in Chitwan and Lamjung Districts of Nepal

To determine the natural infection of the rice root-knot nematode (Meloidogyne graminicola Golden & Brichfield) in rice nurseries, a survey was carried out in Chitwan and Lamjung in June and July of 2022. Rice nurseries were randomly selected based on geographical location, agro-ecological region, land type, cropping practice, and soil type. Forty rice nurseries were surveyed i.e. twenty from each district and 100 seedlings from each nursery as the sample for the study using the simple random method of sampling were evaluated. Field survey revealed that M. graminicola was widely distributed in most rice growing areas of Chitwan and Lamjung districts. Most of the rice nurseries in Lamjung district were found to be infested with M. graminicola as compared to that of the Chitwan district. Disease severity was reported up to 23.26% in Lamjung and 20.2% in Chitwan district. Additionally, the study showed that dry bed conditions were more likely to be affected by rice root-knot disease than wet bed conditions. The majority of farmers planted seedlings on upland (dry) soil, where second-stage juvenile (J2) populations and rice root-knot disease were more common. Most farmers (87.5%) have limited knowledge about rice root knot nematodes and their control methods. This suggested a significant loss in rice output and a high danger of nematode multiplication. This information will provide knowledge about the prevalence of nematode and enabling rice growers in this region to design and implement an appropriate control strategy for managing M. graminicola.

Phylogenetic analyses and pathogenic diversity of Meloidogyne graminicola of rice (cv. BRRI Dhan28) from different agro-ecological zones of Bangladesh

Rice root-knot caused by Meloidogyne graminicola is a major yield-limiting factor in all rice growing countries around the world, which is often ignored in Bangladesh due to its subtle and obscure above ground symptoms. The current study proposes a comprehensive diagnosis of rice root-knot nematode at the molecular level and analyzes the pathogenic diversity of M. graminicola population of different AEZs. Rice seedlings of a popular variety (BRRI Dhan28) showing galls in the roots were collected from thirty Agro-Ecological-Zones (AEZs) of Bangladesh. For molecular identification, nuclear DNA was collected from single second-stage juvenile and internal transcribed spacer (ITS) was used as a universal primer. Molecular identification and phylogenetic analyses revealed that all nematode populations of galled rice seedlings from different locations belong to M. graminicola. The nematode populations constitute six phylogenetic clades. Nematode population of phylogenetic clade II showed the highest no. of galls (178 ± 1.67), although galling index was higher and similar in clade I, clade-II, clade-III and clade-VI. The highest percent reduction in both vegetative and yield-contributing traits were recorded in clade-II. A negative correlation was found in galling incidence and all growth and yield parameters. Comparative hatching of M. graminicola from different locations reveals that the pathogenicity of M. graminicola depends on the genetic variability of the nematode population, but not on the hatched juveniles. It might be concluded that the rice root-knot nematodes (M. graminicola) are prevalent in all agro-ecological zones of Bangladesh, despite the most pathogenic groups being frequent in AEZ- 1, 6, 7, 10, 18, 19, 21 and appropriate management initiatives are therefore crucial for maximizing rice yield.

Identification of a Promising Novel Genetic Source for Rice Root-Knot Nematode Resistance through Markers Associated with Trait-Specific Quantitative Trait Loci.

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 F2:3 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 F2:3 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.

Nematicidal Activity of Volatiles against the Rice Root-Knot Nematode and Environmental Safety in Comparison to Traditional Nematicides.

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.

Survey for Alternate Weed Hosts of Rice Root-Knot Nematode, Meloidogyne graminicola Associated with Rice Crops in Haryana, India

Rice root-knot nematode, Meloidogyne graminicola is one of the most serious nematode pest associated with rice throughout the world. With other species of root-knot nematode, M. graminicola can also infect wide range of weed flora which is commonly grown in or near the rice field. To study the alternate weed hosts of M. graminicola a survey was conducted in the major rice growing blocks of Fatehabad and Sirsa districts of Haryana during Kharif season 2022. A total of 726 samples were collected from rice fields, both from transplanted (TR) and direct seeded rice (DSR) from Phoolan, Bharpur, Ratta Khera, and Jandwala Sotter villages of Fatehabad and Bahauddin and Sikanderpur, Dhottar, Ding and Chopta villages of Sirsa. Out of which 353 samples were found free from nematode infestation while 373 samples (209 from DSR and 164 from TR)were found infested. The juveniles and galls were recorded ranging from 4-190 on the roots of different weed plants. Hence, it is concluded from the present investigation, that nematodes favor more DSR and its weed flora than TR for infection and survival.

Diversity of bioprotective microbial organisms in Upper Region of Assam and its efficacy against Meloidogyne graminicola.

Meloidogyne graminicola has a well-established negative impact on rice yield in transplanted and direct-seeded rice, resulting in yield losses of up to 20 to 90 percent. Studies were undertaken to isolate potential native strains of bio-control agents to manage the devastating Rice Root Knot Nematode (M. graminicola). Eighteen bacterial strains and eleven fungal strains were isolated from the rhizosphere of crops like rice, okra, ash gourd, chili, beans and cucumber, enveloping diverse soil types from the Upper Brahmaputra Valley region of Assam. Six bacterial strains were gram-positive according to morphological results, while twelve others stained negatively. Fifteen bacteria were rod-shaped, two were coccus and one was diplococcus, and all the bacterial isolates showed signs of movement. All the bacterial strains exhibited positivity for gelatin hydrolysis and catalase test. Seven bacteria showed positive, while eleven showed negative reactions to possess the ability to deduce carbon and energy from citrate. The study of the in vitro efficacy of the twenty-nine bacterial and fungal isolates tested against second-stage juveniles (J2) of Meloidogyne graminicola revealed that all the bacterial and fungal isolates potentially inhibited the test organism and caused significant mortality over sterile water treatment. The promising bacterial and fungal isolates that exhibited mortality above 50% were identified as BSH8, BTS4, BTS5, BJA15, FJB 11 and FSH5. The strain BSH8 exhibited the best result of mortality, with 80.79% mortality against J2 of M. graminicola. The strain BTS4 and BTS5 expressed mortality of 71.29% and 68.75% under in-vitro conditions and were significant. The effective and promising bioagents were identified using the 16 S rRNA sequencing as Bacillis subtilis (BSH8), Bacillus velezensis (BTS4), Alcaligenes faecalis (BTS5), Rhizobium pusense (BJA15), Talaromyces allahabadensis (FSH5) and Trichoderma asperellum (FJB11). These results indicated the microorganism's potential against M. graminicola and its potential for successful biological implementation. Further, the native strains could be tested against various nematode pests of rice in field conditions. Its compatibility with various pesticides and the implication of the potential strains in integrated pest management can be assessed.

In vitro Screening of Different Rhizobacterial Strains against Egg Hatching of Rice Root-Knot Nematode, Meloidogyne graminicola

Meloidogyne graminicola is an economic yield loss causing major pest of rice globally. For managing this pest, biological control practices act as an alternate strategy, as it is the most effective and economic. Plant growth promoting rhizospheric bacteria (PGPR) are most significant because they benefit plants both directly and indirectly by enhancing plant growth and provides long lasting antagonistic effects against plant parasitic nematodes. Considering this an in vitro efficacy research experiment of nematoxicity of native rhizobacterial strains was conducted, against egg hatching of M. graminicola at S/2 and S/4 concentration levels of intact bacterial culture and cell free culture filtrates (CFCs). The hatching behavior of rice root-knot nematode eggs was observed on alternate days for ten days which resulted in inhibition of egg hatching by all bacterial cultures at both concentration levels. When compared to the untreated control, Bacillus spp. showed the most egg inhibition in the S/2 concentration of both culture filtrates i.e,86.8% and 84.8%. Similarly, in the S/4 level of concentration, most egg hating such as 83.7% and 79.8% was recorded in Bacillus spp. culture filtrates. The rate of hatching was inversely proportional to the concentration of strains at exposure time, decreasing as the concentration increased. The results of the experiment revealed the potential of rhizospheric bacteria which makes it more feasible and environmentally safe approach for the management of Meloidogyne graminicola.

Comprehensive periodic evaluation of Oryza sativa germplasms for resistance against rice root-knot nematode, Meloidogyne graminicola

Rice root knot nematode, Meloidogyne graminicola is an important nematode pest with a devastating potential that causes serious damage to rice crop. There is an intensive search for eco-friendly, sustainable alternative to the existing nematode management practices. Host plant resistance offers propitious results in managing this minuscule crop enemy. Preliminary screening of 1731 Oryza sativa germplasms followed by periodic evaluation of nine resistant / tolerant germplasms shed new insights on nematode resistance. We observed seasonal inconsistency in the resistance in previously reported germplasms 'Ramakrishna', 'TKM6', 'Abhisek', 'Laxman sal', 'Ratna', and 'TKM1'. Hence, we strongly recommend repeated screening of identified resistant/tolerant rice germplasm lines against M. graminicola in both winter and summer season to confirm the consistency in resistance scale. Further investigation is needed to nullify other chance factors like nematode pathotypes.

Evaluation of different basmati varieties of rice against root-knot nematode (Meloidogyne graminicola)

A pot study was under taken to evaluate twenty promising basmati rice varieties against rice root knot nematode. The result revealed that the varieties showed varied response to root knot nematode. Out of twenty basmati varieties, four viz., Pusa basmati 1121, Vallabh basmati 22, Pusa basmati 1509, Vallabh basmati 23 showed susceptible reaction and rest sixteen varieties shown moderately susceptible reaction against rice root-knot nematode.

Efficacy of Bio-agents in the Management of Root Knot Nematode (Meloidogyne graminicola) in Basmati Rice

Background: Rice root knot nematode (M. graminicola) is considered as a major threat in basmati rice. The main characteristic symptoms produced by M. graminicola are terminal hook shaped or spiral galls on the roots and other symptoms of damage include patches of stunted and yellowish plants. Methods: A field experiment was conducted in Kharif season of 2018 and 2019 at Sardar Vallabhbhai Patel University of Agriculture and Technology, Meerut (UP) to test the efficacy of bio-agents against the root knot nematode. In this experiment, three bio-agents (Bacillus pumilus, Bacillus subtilis and Pseudomonas florescence) and one chemical (carbofuran) were tested in randomized block design with three replications. Result: It was observed that tested bio-agents and chemical significantly reduced the galls per plant in comparison to the control. At 30 and 60 day after transplanting, minimum (12.7 and 10.0 galls/plant) and (20.9 and 18.8 galls/plant) were recorded with Bacillus subtilis @ 20g/ M2 (2 x 108 cfu/g) during 2018 and 2019, respectively. In case of control, 52.7 and 62.5 galls/plant were recorded at 60 days after transplanting during both years. All the tested bio-agents were found effective in reducing the nematode population, increase the growth parameters and yield of basmati rice.

Efficacy of Essential Oils and Their Major Compounds against Meloidogyne graminicola (Rice Root-Knot Nematode) in Pots and Field Trials

Efficacy of Essential Oils and Their Major Compounds against Meloidogyne graminicola (Rice Root-Knot Nematode) in Pots and Field Trials

High Throughput Screening of Introgression Lines of Rice for Resistance against Rice Root-Knot Nematode (Meloidogyne graminicola Golden & Birchfield)

High Throughput Screening of Introgression Lines of Rice for Resistance against Rice Root-Knot Nematode (Meloidogyne graminicola Golden & Birchfield)

Chemical composition and nematicidal activity of essential oils and their major compounds against Meloidogyne graminicola (Rice Root-Knot Nematode)

ABSTRACT Essential oils fromSyzygium aromaticum, Cymbopogon flexuosus and Cymbopogon martinii were isolated by hydrodistillation method and analysed by GC-FID and GC-MS. Eugenol (87.1%) and citral (69.4%), respectively were identified as major compounds in clove and lemongrass oils while geraniol (81.6%) and geranyl acetate (12.4%) in palmarosa oil. Essential oils were evaluated for nematicidal activity against J2s of Meloidogyne graminicola. Results showed the mortality of J2s in clove and lemongrass oils ranged from 70.00-92.50% to 77.50-97.50% and 63.75-92.50% to 72.5-97.50% and that of palmarosa oil showed 70.00-95.00% to 73.75-98.75% mortality at 31.12 to 500 ppm after 24 and 96 hours. Geraniol, citral (sum of neral and geranial) and eugenol were also evaluated for their nematicidal activity. Results showed that geraniol (75.00-95.00% to 78.75-98.75%) possessed highest mortality followed by citral (67.5-93.75% to 72.50-97.50%) and eugenol (66.25-93.75% to 73.75-98.75%) at 31.12 to 500 ppm. Efficacy of the oils and compounds were comparable with carbofuran at 62.5ppm (76.0-87.67%) and 31.25ppm (70.67-83.33%) after 24-96 hours. Results showed that palmarosa oil possessed highest mortality followed by lemongrass and clove oils due to the presence of their major compounds.

T-DNA activation tagging in rice results in a variable response to Meloidogyne graminicola infection

Plant-parasitic nematodes (PPNs) are known to be devastating pests of agricultural crops; the rice root knot nematode Meloidogyne graminicola being the most damaging in rice. Variability in response to any trait is important not only to understand plant-stress interactions, but also its utility in stress mitigation. In this direction, the focus of the study was to exploit activation tagging, a well-established functional genomics approach in rice as a plausible strategy to assess variability in the phenotypic and molecular response to M. graminicola infection. T-DNA insertional mutants were developed in rice (acc. JBT 36/14) using an apical meristem-targeted in planta transformation strategy. A panel of 30 mutants that demonstrated molecular evidences for T-DNA integration and portraying a robust phenotype were chosen for the study. Vigorous phenotyping of these mutants against M. graminicola second stage juveniles both under in vitro pluronic gel medium and soil conditions depicted variable response based on four disease scoring parameters and the derived nematode reproductive factor. Among 30 mutants that were evaluated, five showed a resistant phenotype while 25 depicted a susceptible reaction. The resistant plants clearly demonstrated a reduction in all the disease parameters both under in vitro as well as greenhouse conditions. Quantification of transcripts of 25 genes associated with host defence responses belonging to salicylic acid (SA), jasmonic acid (JA) and ethylene (ET) pathways also indicated corroboration with the phenotype exhibited by the mutants. Distinct pattern of gene expression profiles was observed not only between the susceptible and resistant mutants, but also amongst the resistant ones, demonstrating the possibility of lesser known defense pathways being operated in these plants, apparently depending upon the T-DNA integration loci. The variability in the response to nematode challenge demonstrated in this study can be a step towards deciphering of compatible/incompatible relationships that can form a knowledge base towards not only understanding plant-nematode interactions but also extrapolation of their utility in rice improvement programmes.

Status and yield loss assessment of Rice root knot nematode, Meloidogyne graminicola infestation in Siddharthnagar District, Uttar Pradesh

A total of 80 paddy fields from 14 blocks, located in five tehsils, were surveyed. Meloidogyne graminicola was found widely distributed in most of the rice fields in all the blocks. In nurseries, the frequency of occurrence of rootknot was recorded in 12.2% (Naugarh), 12.1% (Shohratgarh) and 12.3% (Bansi), whereas in the fields, highest frequency of disease was observed in the tehsil Shohratgarh (17%), followed by Bansi (16%), Itwa (12%) and Naugarh (3%). Similarly, the maximum disease incidence was observed in Itwa (28%) tehsil followed by Shohratgarh (24%), Naugarh (22%), Domariayaganj (21%) and Bansi (19%). Gall and root-knot indices (at 0–10 scale) were highest in Shohratgarh (3.4 & 2.8, respectively) followed by Itwa (2.4 & 1.8, respectively) and Naugarh (2.2 & 1.8, respectively). Average soil population of M. graminicola was highest in the tehsil Shohratgarh (1518 J2/kg soil), followed by Itwa (1214 J2/kg soil) and lowest population was recorded in Domariayaganj (714 J2/kg soil) at the time of harvesting. The relative yield loss was also determined during the survey and highest yield loss was recorded in Itwa (17.9%), followed by Domariyaganj (9.7%) and Shohratgarh (9.5%) tehsils.

Rice Root-knot Nematode Down Regulates GA-Gene to Establish Infection

Experiments were conducted to observe the role of gibberellin (GA) in the response of rice to infection by rice root-knot nematode, Meloidogyne graminicola. Gibberellin might have a negative effect on defence in Nipponbare against M. graminicola. On the other hand, an inhibitory effect to M. graminicola in Taichung 65 (wild type) was found when GA was applied exogenously. Galling was significantly and reproducibly lower in mutants, whether it was GA insensitive or GA deficient, than in Taichung 65. There were even significantly lower galls in these GA deficient mutants after GA treatment than in non-treated mutant plants. The expression of GA signaling gene Osgid1-7 was significantly higher only in whole root at 2 dpi (days post inoculation) but not in leaves or root tips. Even this gene was not differentially expressed in root and leaf tissues at later stage (6 dpi days post inoculation) of infection. The nematode inhibited biosynthesis of OsGA20ox in leaves at 2 dpi and, in both of leaves and roots at 6 dpi. The GA response gene AK073385 was also less expressed in root tip at 6 dpi (days post inoculation). These might help M. graminicola to continue their infection in Taichung 65.

Transcriptional analysis through RNA sequencing of giant cells induced by Meloidogyne graminicola in rice roots

One of the reasons for the progressive yield decline observed in aerobic rice production is the rapid build-up of populations of the rice root knot nematode Meloidogyne graminicola. These nematodes induce specialized feeding cells inside root tissue, called giant cells. By injecting effectors in and sipping metabolites out of these cells, they reprogramme normal cell development and deprive the plant of its nutrients. In this research we have studied the transcriptome of giant cells in rice, after isolation of these cells by laser-capture microdissection. The expression profiles revealed a general induction of primary metabolism inside the giant cells. Although the roots were shielded from light induction, we detected a remarkable induction of genes involved in chloroplast biogenesis and tetrapyrrole synthesis. The presence of chloroplast-like structures inside these dark-grown cells was confirmed by confocal microscopy. On the other hand, genes involved in secondary metabolism and more specifically, the majority of defence-related genes were strongly suppressed in the giant cells. In addition, significant induction of transcripts involved in epigenetic processes was detected inside these cells 7 days after infection.

RETRACTED ARTICLE: Molecular cloning and expression analysis of novel putative effector genes from Meloidogyne graminicola

The authors in agreement with the Editor-in-Chief wish to retract this article because it was submitted without approval by the complete research team. Moreover, the senior researchers who were unaware of this paper being submitted by MSc student Masuder Rahmann to the “Journal of Applied Genetics” already published a large part of the results in “Identification of candidate effector genes in the transcriptome of the rice root knot nematode Meloidogyne graminicola” by Haegeman A, Bauters L, Kyndt T, Rahman MM, Gheysen G; Molecular Plant Pathology, 2013, 14(4), 79–90. doi:10.1111/mpp.12014.

Identification of candidate effector genes in the transcriptome of the rice root knot nematode Meloidogyne graminicola

Plant-parasitic nematodes secrete so-called effectors into their host plant which are able to suppress the plant's defence responses, alter plant signalling pathways and, in the case of root knot nematodes, induce the formation of giant cells. Putative effectors have been successfully identified by genomics, transcriptomics and proteomics approaches. In this study, we investigated the transcriptome of the rice root knot nematode Meloidogyne graminicola by 454 sequencing of second-stage juveniles as well as mRNA-seq of rice infected tissue. Over 350 000 reads derived from M. graminicola preparasitic juveniles were assembled, annotated and checked for homologues in different databases. From infected rice tissue, 1.4% of all reads generated were identified as being derived from the nematode. Using multiple strategies, several putative effector genes were identified, both pioneer genes and genes corresponding to already known effectors. To check whether these genes could be involved in the interaction with the plant, in situ hybridization was performed on a selection of genes to localize their expression in the nematode. Most were expressed in the gland cells or amphids of the nematode, confirming possible secretion of the proteins and hence a role in infection. Other putative effectors showed a different expression pattern, potentially linked with the excretory/secretory system. This transcriptome study is a good starting point to functionally investigate novel effectors derived from M. graminicola. This will lead to better insights into the interaction between these nematodes and the model plant rice. Moreover, the transcriptome can be used to identify possible target genes for RNA interference (RNAi)-based control strategies. Four genes proved to be interesting targets by showing up to 40% higher mortality relative to the control treatment when soaked in gene-specific small interfering RNAs (siRNAs).

Nematicides control rice root-knot, caused by Meloidogyne graminicola

Studies were conducted to determine damage potential of Meloidogyne graminicola on the commonly grown rice cv. Sugandh-5 and to devise an effective management strategy. The nematicides were applied through root-dip (200 ppm solution) and soil application of 2 kg ha-1 phorate 10G (25 mg a.i./pot), carbofuran 3G (83.3 mg a.i./pot and 1 L ha-1), carbosulfan 20EC (5µL/pot) and chlorpyriphos 20 EC (6.25 µL/pot) in both nematode infested and non-infested soil with five modes of application viz., root-dip, single soil application (15 days after transplanting), root-dip + one soil application, two soil applications, and root-dip + two soil applications (15 and 30 days). Application of nematicides did not cause any toxicity symptoms on rice plants. In nematode infested soil, terminal and spiral galls developed on the rice roots, and plants suffered 20−31% decrease in the plant growth parameters. Carbofuran and phorate through root-dip plus single soil application provided greatest suppression in galling (16−20%), egg mass production (18−22%) and soil population (27.5−58.2%) of M. graminicola , and subsequently increased all the plant growth variables by 9−19%. Root-dip + two soil applications increased plant growth and suppressed nematodes, but was equal to root dip + one soil application. Root-dip treatment alone with carbosulfan also significantly suppressed root galling (10−12%) and improved the dry weight of roots and shoots (7−10%).