Control Of Root-knot Nematodes Research Articles

Control of the plant-parasitic nematode Meloidogyne incognita in soil and on tomato roots by Clonostachys rosea.

Clonostachys rosea is a well-known mycoparasite that has recently been investigated as a bio-based alternative to chemical nematicides for the control of plant-parasitic nematodes. In the search for a promising biocontrol agent, the ability of the C. rosea strain PHP1701 to control the southern root-knot nematode Meloidogyne incognita was tested. Control of M. incognita in vitro and in soil by C. rosea strain PHP1701 was significant and concentration dependent. Small pot greenhouse trials confirmed a significant reduction in tomato root galling compared to the untreated control. In a large greenhouse trial, the control effect was confirmed in early and mid-season. Tomato yield was higher when the strain PHP1701 was applied compared to the untreated M. incognita-infected control. However, the yield of non-M. incognita-infected tomato plants was not reached. A similar reduction in root galling was also observed in a field trial. The results highlight the potential of this fungal strain as a promising biocontrol agent for root-knot nematode control in greenhouses, especially as part of an integrated pest management approach. We recommend the use of C. rosea strain PHP1701 for short-season crops and/or to reduce M. incognita populations on fallow land before planting the next crop.

Flooding soil with biogas slurry suppresses root-knot nematodes and alters soil nematode communities

Root-knot nematodes (RKNs) pose a serious threat to crop production. Flooding soil with biogas slurry, combined with soil heating before crop planting, has the potential for RKN disease suppression. However, the actual effect of this method has not been verified under field conditions. Here, we present the results of a two-year field experiment in a greenhouse demonstrating the control effect on RKN disease and plant growth using this method, as well as its influence on the soil nematode community. Four treatments were set: untreated control (CK), local control method for RKN (CC), soil flooded with 70 % biogas slurry (BS70), and soil flooded with undiluted biogas slurry (BS100). In the first year, all three RKN control treatments significantly reduced the root-knot index (p < 0.05). In the next year, only BS70 and BS100 still presented significantly suppressed effects (p < 0.05), and it was more obvious under BS70 with a relative control effect of 74.6 %. In the first year, BS70 and BS100 significantly inhibited the plant height of watermelon (p < 0.05). In the next year, however, all three RKN control treatments promoted the growth of watermelon, and their stem diameter was significantly greater than that of CK. The application of biogas slurry (BS70 and BS100) significantly increased nematode richness and the Shannon index in the second year (p < 0.05). However, the structure index showed no significant difference among treatments (p > 0.05), indicating that biogas slurry application did not increase the soil food web complex. Principal component analysis showed that the application of biogas slurry changed the nematode community, especially under BS70, which presented a more lasting influence. The high-level input of biogas slurry also caused soil NH4+-N and heavy-metal and arsenic accumulation in the first year, but these soil-pollution risks disappeared in the second year.

Long-term benefit contribution of chemical and biological nematicide in coffee nematode management in soil microbial diversity and crop yield perspectives

The plant-parasitic root-knot nematode Meloidogyne exigua causes significant damage and is an important threat in Coffea arabica plantations. The utilization of plant-beneficial microbes as biological control agents against sedentary endoparasitic nematodes has been a longstanding strategy. However, their application in field conditions to control root-knot nematodes and their interaction with the rhizospheric microbiota of coffee plants remain largely unexplored. This study aimed to investigate the effects of biological control agent-based bioproducts and a chemical nematicide, used in various combinations, on the control of root-knot nematodes and the profiling of the coffee plant rhizomicrobiome in a field trial. The commercially available biological products, including Trichoderma asperellum URM 5911 (Quality), Bacillus subtilis UFPEDA 764 (Rizos), Bacillus methylotrophicus UFPEDA 20 (Onix), and nematicide Cadusafos (Rugby), were applied to adult coffee plants. The population of second-stage juveniles (J2) and eggs, as well as plant yield, were evaluated over three consecutive years. However, no significant differences were observed between the control group and the groups treated with bioproducts and the nematicide. Furthermore, the diversity and community composition of bacteria, fungi, and eukaryotes in the rhizosphere soil of bioproduct-treated plants were evaluated. The dominant phyla identified in the 16 S, ITS2, and 18 S communities included Proteobacteria, Acidobacteria, Actinobacteria, Ascomycota, Mortierellomycota, and Cercozoa in both consecutive years. There were no significant differences detected in the Shannon diversity of 16 S, ITS2, and 18 S communities between the years of data. The application of a combination of T. asperellum, B. subtilis, and B. methylotrophicus, as well as the use of Cadusafos alone and in combination with T. asperellum, B. subtilis, and B. methylotrophicus, resulted in a significant reduction (26.08%, 39.13%, and 21.73%, respectively) in the relative abundance of Fusarium spp. Moreover, the relative abundance of Trichoderma spp. significantly increased by 500%, 200%, and 100% at the genus level, respectively, compared to the control treatment. By constructing a co-occurrence network, we discovered a complex network structure among the species in all the bioproduct-treated groups. However, our findings indicate that the introduction of exogenous beneficial microbes into field conditions was unable to modulate the existing microbiota significantly. These findings suggest that the applied bioproducts had no significant impact on the reshaping of the overall microbial diversity in the rhizosphere microbiome but rather recruited selected microrganisms and assured net return to the grower. The results underscore the intricate nature of the rhizosphere microbiome and suggest the necessity for alternate biocontrol strategies and a re-evaluation of agricultural practices to improve nematode control by aligning with the complex ecological interactions in the rhizosphere.

Isolation of Pasteuria penetrans, an obligate hyper-parasite, infecting root knot nematode, Meloidogyne spp. from the rhizosphere of pulses in India

BackgroundPasteuria penetrans is a mycelial, endospore forming, obligate, bacterial parasite that has shown enormous potential for biological control of root-knot nematode, Meloidogyne spp. In the present study, the effort has been made to isolate effective and high temperature tolerant indigenous strains from pulse rhizosphere in India.ResultsSurveys were carried out in four different agro-climatic zones and collected 106 root-knot nematode infected soil and plant samples from pulses rhizosphere. Of these, we observed Pasteuria spore attachment on root knot nematode juveniles from seven samples: three from Varanasi, two from Salem and one each from Deoria and Kushinagar. The pure cultures of these seven isolates (named as IIPR-Pp-1 to IIPR-Pp-7 from single infected female, respectively) were developed in 7 cm pot and soil-less CYG medium. The nematode host species was identified as Meloidogyne incognita by perineal pattern and confirmed by sequencing of ITS region. The host range study with M. incognita and Heterodera cajani showed the spore attachment was specific to M. incognita revealed that the species of the parasite was Pasteuria penetrans. SEM study on morphometrics of Pasteuria spores belong to two groups. In vitro assay on endospore attachment assay with pre-treated endospores at 20, 30, 40, 50, 60 and 70 °C revealed that maximum number of endospore attachment of all isolates was observed at 30 °C followed by 40 °C, and the least number of them was observed at 60 °C and above. The isolate Pp3 exhibited maximum number of spore attachments among all isolates at 30 °C treatment (14) and 40 °C treatment (10.67). Endospore attachment assay with pre-treated J2 at 20, 25, 30, 35, 40 and 45 °C revealed that maximum number of attachment of all isolates was observed at 30 °C treatment, and no attachment was observed at 40 °C and above.ConclusionPasteuria penetrans isolate IIPR-Pp3 exhibited high temperature tolerance and can be used further to develop Pasteuria-based biopesticide for management of root-knot nematode, M. incognita in pulses.

Biological control of root-knot nematodes in common beans using putative nematocidal species of Trichoderma indigenous to Pakistan

ABSTRACT The putative nematocidal strains of Trichoderma for controlling root-knot nematodes were isolated from different agricultural fields in Pakistan. The Trichoderma isolates were confirmed using morphological and molecular characterisation. The root-knot nematodes were isolated from infected common bean plants Phaseolus vulgaris and identified as Meloidogyne incognita through phenotypic characteristics. Both in vitro and in vivo assays were performed. The nematocidal activity of the selected Trichoderma spp. was assessed using culture filtrate and spore suspension assays. Parameters including J2 mortality, egg hatching inhibition, root gall index, and egg mass index were calculated. The culture filtrates of T. bevicrassum strain ISO-03 caused significantly higher J2 mortality (71%) and inhibited egg hatching (68%) as compared to the activities of culture filtrates of the other two strains used in this study. The least control activity was observed in case of the culture filtrates of T. viride strain ISO-05 with 21% J2 mortality and 19% egg hatching inhibition. Similarly, the spore suspensions of T. brevicrassum ISO-03 showed the highest mortality of M. incognita juveniles (64% with respect to control) as well as the egg-hatching inhibition rates of 59%. In the in vivo study, the same strain T. bevicrassum ISO-03 significantly reduced the root galling index and egg mass indices as compared to the control. Furthermore, T. bevicrassum ISO-03 significantly promoted plant growth compared to the control. Overall, T. bevicrassum ISO-03 was identified as a potent biocontrol strain against root-knot nematodes in addition to its plant growth-promoting characteristics.

Foliar application of glycine-functionalized nanopesticides for effective prevention and control of root-knot nematodes via a targeted delivery strategy.

Root-knot nematodes (RKNs) are the highly damaging pests for various crops, and the prevalence of RKNs has posed serious threats to worldwide agricultural harvest, severely affecting global food security and ecosystem health. Traditional pesticide systems on controlling RKNs generally cause environmental hazards and phytotoxicity due to the excessive use of pesticides resulted from low utilization efficiency. And effective approaches with biosafe and efficient features are highly demanded to break away from the dilemma caused by RKNs. In this research, a nanopesticide system with root-targeted delivery function was developed to achieve effective prevention and control of RKNs. The nanocarriers (MSN-KH560-Gly) and the obtained nanopesticides (EB@MSN-KH560-Gly) were proved to be biosafe. Also, this nanopesticide system demonstrated sustained release behavior. The grafting of glycine (Gly) significantly improved the pesticide contents translocating to cucumber roots (about 304.7%). Besides, such root-targeted delivery function resulted in no root nodule in cucumber plants after the foliar application of these nanopesticides (prevention rate of 100%). In addition, the root nodule numbers of the infected cucumber plants decreased by 71.67%. Foliar application of these Gly-functionalized nanopesticides achieved effective prevention and control of RKNs due to the root-targeted delivery property inherent in this nanopesticide system, and such root-targeted delivery strategy opens a novel and efficient method to protect crops from RKN invasion and thus facilitates the development of sustainable agriculture. © 2023 Society of Chemical Industry.

As a Transitional Host, Weed Solanum nigrum L. Increases the Population Base of Root-Knot Nematode Meloidogyne enterolobii for the Next Season

The aim of this study was to determine the status of weed Solanum nigrum L. as a transitional host for Meloidogyne enterolobii and its effect on the population base of the nematodes in the next season. The nematode species infecting S. nigrum L. in a fallow field was identified by morphological identification and molecular diagnosis, and parasitic characteristics of the nematodes in S. nigrum L., including development of the nematode in S. nigrum L., the histopathological response of S. nigrum L. to M. enterolobii, and the host suitability of S. nigrum L., were studied. The M. enterolobii soil population density was evaluated before and after S. nigrum L. planting. Species identification revealed that it was M. enterolobii infection. Developmental observation indicated that juveniles of M. enterolobii developed fast in S. nigrum L., establishing feeding sites by 5 days after inoculation (DAI) and forming obvious egg masses on the root at 25 DAI. Histopathological observation showed the typical susceptible response of S. nigrum L., including giant cells with thick cell walls, uniformly dense cytoplasm, and less vacuolation, mainly inside the vascular cylinder. Host suitability assays suggested that S. nigrum L. is a good host for M. enterolobii with an average reproduction factor (RF) of 48.04 ± 14.71. Population densities assays revealed that S. nigrum L. increased the population density of M. enterolobii for two consecutive years from 0.48 ± 0.25 and 0.53 ± 0.31 J2/cm3 to 1.33 ± 0.16 and 1.56 ± 0.43 J2/cm3 of soil. These results indicated that M. enterolobii could reproduce well by infecting S. nigrum L. during the fallow season, and it increased the population base of M. enterolobii to the next season during vegetable production, which suggested a novel direction for the control of root-knot nematodes by controlling weeds as transitional hosts of M. enterolobii in the fallow season.

Unzipped chromosome-level genomes reveal allopolyploid nematode origin pattern as unreduced gamete hybridization

The formation and consequences of polyploidization in animals with clonal reproduction remain largely unknown. Clade I root-knot nematodes (RKNs), characterized by parthenogenesis and allopolyploidy, show a widespread geographical distribution and extensive agricultural destruction. Here, we generated 4 unzipped polyploid RKN genomes and identified a putative novel alternative telomeric element. Then we reconstructed 4 chromosome-level assemblies and resolved their genome structures as AAB for triploid and AABB for tetraploid. The phylogeny of subgenomes revealed polyploid RKN origin patterns as hybridization between haploid and unreduced gametes. We also observed extensive chromosomal fusions and homologous gene expression decrease after polyploidization, which might offset the disadvantages of clonal reproduction and increase fitness in polyploid RKNs. Our results reveal a rare pathway of polyploidization in parthenogenic polyploid animals and provide a large number of high-precision genetic resources that could be used for RKN prevention and control.

Modelling the biological control of tomato root-knot nematode by predatory mites in the presence of an alternative prey

Modelling the biological control of tomato root-knot nematode by predatory mites in the presence of an alternative prey

Antagonistic potential of endophytic fungi against Meloidogyne enterolobii, M. incognita and Nacobbus aberrans sensu lato

Root-knot nematodes limit horticultural crop production in Mexico where management is mainly based on nematicides that represent a risk to health and the environment. Thus, biological alternatives, such as the use of endophytic fungi, are currently being developed. The objective of this research was to isolate, identify and evaluate the antagonistic potential of endophytic fungi against the root-knot nematodes Meloidogyne enterolobii, M. incognita and the false root-knot nematode Nacobbus aberrans sensu lato (s.l.) occurring in Mexico. Endophytic fungi from chili pepper and tomato plants with a low root galling index were isolated from three localities in Sinaloa state (Villa Juárez, Valle de Culiacan and La Cruz de Elota) and one in Mexico City (Xochimilco). Fourteen isolates from leaves and roots were evaluated to assess: i) the ability to promote growth in chili pepper and tomato plants, ii) the degree of parasitism on nematode eggs and second-stage juveniles (J2), and iii) the nematostatic and nematicidal effect of their filtrates on the J2. In the trials, the three most effective endophytic fungal isolates were Chaetomium globosum (S1TH2), Echria macrotheca (S3RT2) and Stagonospora trichophoricola (XRC3). All three fungal isolates increased growth on chili pepper plants after application, but only two (S3RT2 and XRC3) did so on tomato plants. S1TH2 parasitized M. enterolobii eggs; S3RT2 and XRC3 eggs of N. aberrans s.l.; S3RT2 also parasitized M. incognita eggs and J2 of N. aberrans s.l. The S1TH2 filtrate was nematostatic for M. incognita and N. aberrans s.l., the XRC3 filtrate was nematostatic for N. aberrans s.l., and the S3RT2 filtrate was nematostatic and nematicidal for the J2 of N. aberrans s.l. The results obtained indicate that these isolates could be involved in natural regulation and biological control of root-knot nematodes.

Biocontrol Efficacy of Bacillus methylotrophicus TA-1 Against Meloidogyne incognita in Tomato.

Root-knot nematodes (RKNs) are harmful plant-parasitic nematodes of tomatoes which can cause significant yield losses. Therefore, there is increasing interest in exploring the application of bacterial nematicides. The bacterium Bacillus methylotrophicus TA-1 is a broad-spectrum biological control agent; however, its effect on RKNs control remains largely unclear. In this study, the toxicity of B. methylotrophicus TA-1 against Meloidogyne incognita was investigated in vitro, and the potential of B. methylotrophicus TA-1 to decrease infection of RKNs in tomato were evaluated in pot and field trials. Results showed that B. methylotrophicus TA-1 exhibited high nematicidal activity against second-stage juveniles (J2s) and eggs of M. incognita with 50% lethal concentration (LC50) values of 5.80 and 7.00 × 108 colony forming units (CFU)/ml, respectively. In the pot experiments and field trials conducted in 2020 and 2021, tomato plants treated with B. methylotrophicus TA-1 soil drench applied once at 3, 6, and 9 × 108 CFU/plant had significantly higher plant height and greater yield compared with the untreated control. Tomato yields of the treated plots with B. methylotrophicus TA-1 in 2 consecutive years' field trials were between 53.4 to 66.1 and 52.8 to 61.5 t/ha, while they were 49.7 and 48.2 t/ha in the untreated control for each year, respectively. The lowest population densities of M. incognita at 30 and 60 days after treatment were 119 and 135 J2s per 100 g soil in 2020 and 43 and 118 J2s in 2021 in TA-1-treated plots. The lowest gall index of 4.7 and 3.3 in 2020 and 2021, respectively, and the highest yield were all observed in the TA-1 at 9 × 108 CFU/plant treated plants, with no significant differences with the commercial control abamectin. These results provided a basis for further studies of B. methylotrophicus TA-1 formulations, application doses, frequencies, and mechanisms of action, which are necessary before it could be used as a component of integrated management programs to manage RKNs in tomato production.

Assaying the effects of some essential oils on Root-knot Nematode [Meloidogyne javanica (Treub 1885) Chitwood 1949] in the laboratory

Nematodes are man’s faceless enemy whose activities encourage hunger and poverty. This study was conducted to determine the efficacy of selected plant oil extract in the control of root knot Nematode [Meloidogyne javanica] in the laboratory. The experimental design used was Complete Randomized Design (CRD) with fourteen treatments, replicated three times. Egg hatch inhibition test on M. javanica eggs and juvenile mortality test were separately performed by exposing the eggs and juveniles to different dosage of the essential oils. Neem seed oil statistically proved effective in inhibiting egg hatch followed closely by Garlic clove oil and then Moringa seed oil. All the essential oil treatments were more effective than carbofuran treatment. The surfactant Sodium Lauryl Sulphate was shown to have nematicidal properties as it also recorded zero egg hatching at all the doses applied. The second stage juveniles of M. javanica recorded a higher mortality rate (100%), when they were treated with Neem seed oil, closely followed by Garlic clove oil and then Moringa seed oil. All Surfactant treatments caused 100% juveniles’ mortality. The higher the doses of the essential oils, the higher the juvenile mortality rate. Neem seed oil at all the dosage proved effective in controlling Meloidogyne javanica causing high rate of juvenile mortality and suppressing M. javanica egg hatch. The nematicidal characteristics exhibited by the essential oils might be due to the phytochemicals present in the oils.

Biocontrol efficacy of endophytic fungus, Acremonium sclerotigenum, against Meloidogyne incognita under in vitro and in vivo conditions

AbstractBiocontrol microorganisms are important tools for the control of root knot nematodes (Meloidogyne spp.). Endophytic fungi have shown great potential as biocontrol agents in such applications. We here isolated an endophytic fungus from tomato root galls infected with M. incognita and identified the isolate as Acremonium sclerotigenum based on morphology and the internal transcribed spacer sequence. The biocontrol potential of this fungus was evaluated both in vitro and in vivo. Specifically, in vitro analyses were conducted to determine the potential of A. sclerotigenum to increase Meloidogyne incognita juvenile (J2 stage) mortality and decrease M. incognita egg hatching rates. The results revealed that A. sclerotigenum culture filtrates caused high J2 mortality rates (up to 95.5%) and significantly inhibited egg hatching (by up to ~ 43%). Furthermore, eggs treated with the culture filtrate were disaggregated and could not develop into nematodes. An in vivo experiment showed that treatment of tomato plants with A. sclerotigenum suppressed root knot nematode populations and significantly reduced the galling index. Both A. sclerotigenum treatment and exposure to the nematicide abamectin had good control effects, with efficacy rates of 55.43% and 70.58%, respectively. In summary, the endophytic fungus A. sclerotigenum here showed excellent potential for biocontrol of M. incognita. Further studies should be conducted to identify the nematicidal compounds produced by this fungus and to establish the molecular mechanism of action associated with the observed biocontrol effects.

Charcoal rot and root-knot nematode control on faba bean by photosynthesized colloidal silver nanoparticles using bioactive compounds from Moringa oleifera leaf extract

Charcoal rot and root-knot nematode control on faba bean by photosynthesized colloidal silver nanoparticles using bioactive compounds from Moringa oleifera leaf extract

Self-Assembled Nanonematicide Induces Adverse Effects on Oxidative Stress, Succinate Dehydrogenase Activity, and ATP Generation.

Long-term overuse of chemical nematicides has resulted in low control efficacy toward destructive root-knot nematodes, and continuous development in nanotechnology is supposed to enhance the utilization efficiency of nematicides to meet practical needs. Herein, a cationic star polymer (SPc) was constructed to load fluopyram (flu) and prepare a flu nanoagent. Hydrogen bonding and van der Waals forces facilitated the self-assembly of the flu nanoagent, leading to the breakdown of self-aggregated flu and reducing its particle size to 60 nm. The bioactivity of flu was remarkably improved, with the half lethal concentration 50 from 8.63 to 5.70 mg/L due to the help of SPc. Transcriptome analysis found that a large number of transport-related genes were upregulated in flu nanoagent-exposed nematodes, while the expression of many energy-related genes was disturbed, suggesting that the enhanced uptake of flu nanoagents by nematodes might lead to the disturbance of energy synthesis and metabolism. Subsequent experiments confirmed that exposure to flu nanoagents markedly increased the reactive oxygen species (ROS) level of nematodes. Compared to flu treatment alone, succinate dehydrogenase (SDH) activity was inhibited in flu nanoagent-exposed nematodes with an increase in the pIC50 from 8.81 to 11.04, which further interfered with adenosine triphosphate (ATP) biosynthesis. Furthermore, the persistence of SPc-loaded flu in soil was prolonged by 2.33 times at 50 days after application. The protective effects of flu nanoagents on eggplant seedlings were significantly improved in both greenhouse and field trials, and the root-knot number was consistently smaller in roots treated with flu nanoagents than in those treated with flu alone. Overall, this study successfully constructed a self-assembled flu nanoagent with amplified effects on oxidative stress, SDH activity, and ATP generation, leading to highly effective control of root-knot nematodes in the field.

Domateste Kök Ur Nematodu Mücadelesinde Kitosanın Toprak ve Yaprak Uygulamaları

In this research, the effect of soil, foliar and simultaneous soil+foliar applications of chitosan on gall and egg mass of root-knot nematode Meloidogyne incognita was investigated in tomato plants under controlled conditions (24±1°C, 60±5% RH). Fluopyram (0.16 ml/L) was used as positive control while only nematode-treated plants were considered as negative control. The study was set up in a randomized plot design with 5 replications for each application. The liquid suspension of chitosan diluted at 1% was used. In soil application, 5 ml was applied to each pot by using a graduated cylinder while in foliar application, the liquid suspension at 1% was applied using a portable hand sprayer until the solution was finished. The study was evaluated according to the 1-9 gall and egg mass index 60 days after inoculation of nematodes. The lowest gall (2.8) and egg mass (2.4) indexes were detected in the simultaneous soil+foliar application and took place in the same statistical group with the positive control nematicide. It was determined that the nematicidal effect of chitosan has increased in the case of combined soil and foliar applications. These results support the fact that chitosan applications are successful in the control of root-knot nematode.

Biochar from grape pomace, a waste of vitivinicultural origin, is effective for root-knot nematode control

Root-knot nematodes (RKNs) are obligate endoparasites that feed on their host plants to complete its life cycle, representing a major threat to agriculture and economy worldwide. The development of new management strategies becomes essential as effective chemical nematicides are progressively being restricted. Hence, we analysed grape pomace-derived biochars, pyrolysed at 350 °C (BC350) and 700 °C (BC700), focusing on their potential for RKN control. The thermal treatment of grape pomace caused an increase in the concentration of carbon and plant macro- and micronutrients, which were largely present in a water-soluble form. Synchrotron radiation-based Fourier transform infrared microspectroscopy data showed a general loss of carboxylic functional groups during pyrolysis, partially contributing to the alkalinisation of both biochars, mostly in BC700. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy analysis revealed a highly porous structure filled with different crystals composed of elements such as K, Ca, Mg, P, Si or Al, which could be a suitable environment for the growth of microorganisms. Biochar-derived aqueous extracts showed phytotoxicity to tomato seedlings at high concentrations, and disappeared upon dilution, but no toxic effect was observed on the nematode’s infective stage. However, the infective and reproductive traits of a Meloidogyne javanica population in tomato were significantly reduced (i.e. egg masses and eggs per plant) in washed-biochar-treated soil in pots (0.75%; BC350W). Therefore, the large amount of grape waste generated after wine production can be transformed into a valuable product such as biochar, effective for RKNs control, thus reducing the waste management problem and contributing to a circular economy.Graphical abstract

Arbuscular mycorrhizal fungi-mediated activation of plant defense responses in direct seeded rice (Oryza sativa L.) against root-knot nematode Meloidogyne graminicola.

Rhizosphere is the battlefield of beneficial and harmful (so called phytopathogens) microorganisms. Moreover, these microbial communities are struggling for their existence in the soil and playing key roles in plant growth, mineralization, nutrient cycling and ecosystem functioning. In the last few decades, some consistent pattern have been detected so far that link soil community composition and functions with plant growth and development; however, it has not been studied in detail. AM fungi are model organisms, besides potential role in nutrient cycling; they modulate biochemical pathways directly or indirectly which lead to better plant growth under biotic and abiotic stress conditions. In the present investigations, we have elucidated the AM fungi-mediated activation of plant defense responses against Meloidogyne graminicola causing root-knot disease in direct seeded rice (Oryza sativa L.). The study describes the multifarious effects of Funneliformis mosseae, Rhizophagus fasciculatus, and Rhizophagus intraradices inoculated individually or in combination under glasshouse conditions in rice plants. It was found that F. mosseae, R. fasciculatus and R. intraradices when applied individually or in combination modulated the biochemical and molecular mechanisms in the susceptible and resistant inbred lines of rice. AM inoculation significantly increased various plant growth attributes in plants with simultaneous decrease in the root-knot intensity. Among these, the combined application of F. mosseae, R. fasciculatus, and R. intraradices was found to enhance the accumulation and activities of biomolecules and enzymes related to defense priming as well as antioxidation in the susceptible and resistant inbred lines of rice pre-challenged with M. graminicola. The application of F. mosseae, R. fasciculatus and R. intraradices, induced the key genes involved in plant defense and signaling and it has been demonstrated for the first time. Results of the present investigation advocated that the application of F. mosseae, R. fasciculatus and R. intraradices, particularly a combination of all three, not only helped in the control of root-knot nematodes but also increased plant growth as well as enhances the gene expression in rice. Thus, it proved to be an excellent biocontrol as well as plant growth-promoting agent in rice even when the crop is under biotic stress of the root-knot nematode, M. graminicola.

Occurrence of root-knot nematodes (Meloidogyne spp.) on peppers in Hainan, China, and resistance of field cultivars to M. enterolobii and M. incognita.

Root-knot nematodes (Meloidogyne spp.) are the most economically damaging group of plant-parasitic nematodes. They are considered to be a major constraint of pepper (Capsicum annuum L) crops worldwide. In China, Hainan Island is the main producer of pepper, where the climatic conditions and cropping patterns are favorable for infection by Meloidogyne spp. In this study, we conducted a detailed investigation of the occurrence, severity and population distribution of root-knot nematodes infested pepper throughout Hainan Island. Meanwhile, we also tested the level of resistance to M. enterolobii and M. incognita for the field pepper cultivars in Hainan. Our results showed that root-knot nematodes belonging to M. enterolobii, M. incognita and M. javanica were found in Hainan, and the dominant population was M. enterolobii, which is the predominant species in the tropical area. Notably, all the pepper cultivars in this study were highly susceptible to M. enterolobii, which is probably one of the reasons for its rapid spread throughout Hainan. The pepper cultivars exhibited different levels of resistance to M. incognita. In conclusion, this study promotes the comprehensive understanding of the root-knot nematode distribution and host resistance level of Meloidogyne in Hainan, which will guide the effective control of root-knot nematodes.

Preparation and Characterization of Avermectin B2 Microcapsules and Effective Control of Root-Knot Nematodes.

Polyurethane microcapsules of avermectin B2 were prepared by means of interfacial polymerization with methylene diphenyl diisocyanate as the wall material and triethanolamine as the initiator. The microcapsules were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The surfaces of the microcapsules were found to be smooth and almost spherical, and the encapsulation efficiency was high. The avermectin B2 microcapsules exhibited a good diffusion-controlled sustained-release performance, giving a cumulative release rate of 91.81%. The results indicated that the polyurethane capsule protected against the photolysis of avermectin B2. Finally, the microcapsules exhibited good soil leaching properties and were able to control the population of root-knot nematodes with an efficacy of 80.80%.