Important Plant-parasitic Nematodes Research Articles

Occurrence and distribution of Meloidogyne spp. in fields rotated with sweetpotato and host range of a North Carolina population of Meloidogyne enterolobii.

Root-knot nematodes (RKN, Meloidogyne spp.) are some of the most economically important and common plant parasitic nematodes in North Carolina (NC) cropping systems. Soil samples collected from fields planted with crops rotated with sweetpotato [Ipomoea batatas (L.) Lam.] in 39 NC counties in 2015-2018 were processed at the NC Nematode Assay Laboratory. The occurrence of second-stage juvenile (J2) RKN populations was examined based on collection year, month, county, and previous planted crop. The highest number of RKN positive samples originated from Cumberland (53%), Sampson (48%), and Johnston (48%) counties. The highest average RKN population density was detected in Sampson (147 J2/500 cm3 soil) and Nash (135 J2/500 cm3 soil) counties, while Wayne (7 J2/500 cm3 soil) and Greene (11 J2/500 cm3 soil) counties had the lowest average RKN population density. Meloidogyne enterolobii is a new invasive species that is impacting sweetpotato growers of NC. The host status of a NC population of M. enterolobii, the guava-root knot nematode, was determined by examining eggs per gram of fresh root (ER) and the final nematode egg population divided by the initial population egg count (reproductive factor, RF) in greenhouse experiments. This included eighteen vegetable, field, cover crops and weed species. The tomato 'Rutgers' was used as a susceptible control. Cabbage 'Stonehead', pepper 'Red bull', and watermelon 'Charleston gray' and 'Fascination' were hosts and had similar mean ER values to the positive control, ranging from 64 to 18,717. Among field crops, cotton, soybean 'P5018RX', and tobacco were hosts with ER values that ranged from 185 to 706. Members of the Poaceae family such as sweet corn (Zea mays) and sudangrass (Sorghum x drummondii) were non-hosts to M. enterolobii and the mean ER values ranged from 1.85 to 7. The peanut 'Tifguard' and winter wheat (Triticum aestivum) also had lower ER values than the vegetable hosts. Growers should consider planting less susceptible or non-hosts such as peanut, sudangrass, sweet corn, and winter wheat in 2-3 year crop rotations to lower populations of this invasive nematode.

Development and Validation of a Resistance Management Model for the Soybean Cyst Nematode, Heterodera glycines.

Plant-parasitic nematodes are a key yield-limiting pest of crops around the world. Deployment of plant resistance genes are an important management tactic for many economically important plant-parasitic nematodes. The selection for virulence in nematode populations is a major threat to the effectiveness of resistance gene-based management. Little research has gone into resistance management modelling despite the importance of both plant-parasitic nematodes and resistance genes for their management. In this paper, we report on a cyst nematode resistance management model created to explore the factors which are most important for determining the durability of resistance genes to this important family of plant-parasitic nematodes. The relative dominance of virulence expression, the level of inbreeding, and the number of generations per cropping season were the most important factors in predicting resistance gene durability. Aspects of cyst nematode biology that reduce the number of generations per season for a portion of the population had a much smaller effect on the durability of resistance genes. These factors included delayed hatching within a season and early dormancy. The accuracy and utility of the model was tested using the soybean cyst nematode (SCN) rhg1-mediated resistance system. The model accurately predicted the rate at which virulence to the rhg1b resistance gene developed in Iowa over a two-decade period. The model suggested resistance gene pyramids as the most durable management solution for SCN with multiple possible avenues to obtain acceptable efficacy and durability.

Characterisation of Paratylenchus cacao n. sp. from Ghana, and P. enigmaticus (Nematoda: Paratylenchinae) from Belgium

Summary Paratylenchus cacao n. sp., a pin nematode associated with cocoa (Theobroma cacao L.) from Ghana, is described herein based on morphology, morphometrics and phylogenetic relationships with other species. Morphologically, P. cacao n. sp. is characterised by a female body length of 174-265 μm, body assuming a ‘C’ or ‘J’ shape after heat relaxation, a flat head, slightly set off lip region, a truncated anterior end, a rigid stylet of 24-31 μm, four lateral lines, vulval region with distinct vulval flaps, and a finely rounded tail with a mucron-like terminus. The findings of the phylogenetic analyses utilising the D2-D3 expansion segments of 28S, ITS of rDNA, and COI of mitochondrial DNA sequences indicate that P. cacao n. sp. is a species closely related to P. leptos. Additionally, based on butterhead lettuce and leek populations from Belgium, the first description of a male, SEM pictures and COI sequences of P. enigmaticus are presented. Both studies exemplify how even potentially important plant-parasitic nematode species can remain unnoticed for a long time. This suggests the need to conduct more nematode diversity studies and underscores the significance of correct nematode identification through the utilisation of tools such as integrative taxonomy.

Growth, Physiological, and Biochemical Variations in Tomatoes after Infection with Different Density Levels of Meloidogyne enterolobii.

Meloidogyne enterolobii is an extremely important plant parasitic nematode. Tomato (Solanum lycopersicum) is an essential worldwide vegetable, and M. enterolobii poses a major threat to its production. The present research investigated the effects of different levels of inoculum density of M. enterolobii (100, 500, 1000, 1500, and 2000 second-stage juveniles (J2s)/plant) on tomato growth, physiological, and biochemical changes at 7, 14, 21, and 28 days post-inoculation (dpi). The negative impact of M. enterolobii on plants gradually increased when the inoculum level increased. Therefore, M. enterolobii population densities (500-2000 J2s/plant) significantly (p < 0.05) reduced plant growth, photosynthetic pigmentation, gas exchange, and chlorophyll fluorescence compared to control plants, while the low population density (100 J2s/plant) showed very little influence. Furthermore, plants with the highest M. enterolobii inoculum (2000 J2s/plant) exhibited a greater number of egg masses and galls. The inoculum densities of M. enterolobii exhibited a notable correlation with the significant elevation of both malondialdehyde (MDA) and hydrogen peroxide (H2O2) levels, which are recognized as very detrimental stresses in plants. Similarly, a rise in the activity of several defensive antioxidant enzymes, namely superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), indicates the defensive mechanism used to combat the oxidative destruction produced by M. enterolobii. The specific activity of glutathione (GSH) and ascorbate (ASA) increased as potent antioxidant defense molecules in response to induced oxidative damage. In addition, our findings also demonstrated that the highest population density (2000 J2s/plant) increased the secondary metabolites responsible for scavenging oxidative stress in the plants. However, further research is required to explore the underlying reasons for this phenomenon and to develop efficient chemical or biocontrol strategies for managing M. enterolobii.

Long-Term Field Application of a Plant Growth-Promoting Rhizobacterial Consortium Suppressed Root-Knot Disease by Shaping the Rhizosphere Microbiota.

Root-knot nematodes (Meloidogyne spp.) are one of the most economically important plant parasitic nematodes, infecting almost all cultivated plants and resulting in severe yield losses every year. Plant growth-promoting rhizobacteria (PGPR) have been extensively used to prevent and control root-knot diseases and increase yield. In this study, the effect of a consortium of three PGPR strains (Bacillus cereus AR156, B. subtilis SM21, and Serratia sp. XY21; hereafter "BBS") on root-knot disease of cucumber was evaluated. The application of BBS significantly reduced the severity of root-knot disease by 56 to 72%, increased yield by 36 to 55%, and improved fruit quality by 14 to 90% and soil properties by 1 to 90% relative to the control in the cucumber fields of the Nanjing suburb, Jiangsu Province, from 2015 to 2018. BBS altered the rhizosphere bacterial community. Compared with the control group, it significantly (false discovery rate, P < 0.05) increased the abundance of 14 bacterial genera that were negatively correlated with disease severity. Additionally, the redundancy analysis suggested that BBS-treated rhizosphere soil samples were dominated by disease-suppressive bacteria, including the genera Iamia, Kutzneria, Salinibacterium, Mycobacterium, Kribbella, Pseudonocardia, Sporichthya, Sphaerisporangium, Actinomadura, Flavisolibacter, Phenylobacterium, Bosea, Hyphomicrobium, Agrobacterium, Sphingomonas, and Nannocystis, which were positively related to total organic carbon, total nitrogen, total organic matter, dissolved organic carbon, [Formula: see text]-N, and available phosphorus contents. This suggests that BBS suppresses root-knot nematodes and improves the soil chemical properties of cucumber by altering the rhizosphere microbial community.

Evaluation of nematophagous and biocontrol efficacy of Dactylellina phymatopaga against Meloidogyne graminicola on rice (Oryza sativa L.)

Dactylellina phymatopaga is a nematode-trapping fungus which traps, kills and parasitizes nematodes. The rice root-knot nematode, Meloidogyne graminicola, is an important plant-parasitic nematode that threatens rice production worldwide. Therefore, it is most important to find new substitute for chemical control of M. graminicola. The present study aimed to investigate the in vitro trapping, germination and nematophagous ability in soil and fungus efficacy to reduce the number and biomass of developing stages of M. graminicola in rice roots. Isolates of D. phymatopaga were found to produced sessile adhesive knobs on growing hypahe to trap and paralyze M. graminicola J2 up to 98.8 % within 120 h of inoculation, in in-vitro conditions. Test for germination and nematophagous activities in various soils showed that spores of D. phymatopaga frequently germinate in soil with formation of adhesive sessile knobs on their germ lings, capturing and parasitizing nearby free living nematodes. Application of D. phymatopaga in M. graminicola-infested soil at the time and prior to rice sowing showed significant reduction in the number of root galls, number and biomass of developing stages of M. graminicola in rice roots (62.65–80.73 %) increasing plant health as compared to plants grown in nematode infested soil. Application of D. phymatopaga 7 days before sowing showed the highest biocontrol ability by decreasing in the nematode biomass in the associated rice roots per plant and the expended nematode-to-root biomass ratio (NB:RB). The results showed that the nematode-trapping behavior of D. phymatopaga yields a bio-management potential in reducing the number of developing stages of M. graminicola and their biomass in rice roots.

Isolation, Identification, and Evaluation of the Predatory Activity of Chinese Arthrobotrys Species towards Economically Important Plant-Parasitic Nematodes.

The current investigation aimed to isolate and identify predatory fungal strains and evaluate their efficacy in mitigating the effects of plant-parasitic nematodes. We successfully isolated three distinct nematophagous fungal strains from soil samples, identified as Arthrobotrys megalosporus, A. oligospora, and A. sinensis, using conventional and molecular identification methodologies. In vitro trials illustrated the high capture efficiency of these fungi against plant-parasitic nematodes. Over an exposure period of 48 h to Aphelenchoides besseyi, Bursaphelenchus xylophilus, and Ditylenchus destructor, A. megalosporus (GUCC220044) displayed predation rates of 99.7%, 83.0%, and 21.1%, respectively. A. oligospora (GUCC220045) demonstrated predation rates of 97.3%, 97.3%, and 54.6%, and A. sinensis (GUCC220046) showed rates of 85.1%, 68.3%, and 19.0% against the same cohort of nematodes. The experimental outcomes substantiate that all three identified fungal strains demonstrate predatory activity against the tested nematodes, albeit with varying efficiencies.

First Record of Meloidogyne javanica (Treub, 1885) (Chitwood, 1949) in Lettuce (Lactuca sativa L.) Growing Areas in the Southern Marmara Region

First Record of Meloidogyne javanica (Treub, 1885) (Chitwood, 1949) in Lettuce (Lactuca sativa L.) Growing Areas in the Southern Marmara Region&#x0D; ABSTRACT&#x0D; The estimated loss of the annual agricultural production due to plant parasitic nematodes, which are among the important soil-borne pathogens, is estimated to be approximately 118 billion US dollars. Root-knot nematodes are the most important plant parasitic nematode group due to their wide host range and difficulties in control and cause significant quality and yield losses in vegetables including lettuce plant. Root-knot nematodes are causing symptoms such as yellowing, wilting and stunting on lettuce plant. For monitoring lettuce fields for detecting nematode infected areas, surveys were made to the lettuce growing areas of Çanakkale province in the winter months of 2021-2022 and the plants infected with root-knot nematodes were examined and pure nematode cultures were obtained in the laboratory. Species identification was made using morphological methods and morphometric measurements from second-stage infective juvenile and female individuals obtained from pure cultures. As a result, the first record of M. javanica in lettuce growing areas in the Southern Marmara Region was made in this study.&#x0D; Keywords: Lettuce, Southern Marmara Region, Root-knot nematode

Development of a Droplet Digital PCR Assay for Detection and Quantification of Stubby Root Nematode, Paratrichodorus allius, in Soil.

The stubby root nematode Paratrichodorus allius is an important plant-parasitic nematode species within the Trichodoridae family. It can directly harm the plants by feeding on the roots or indirectly by transmitting Tobacco rattle virus. These nematodes are mostly diagnosed either by traditional microscopic methods or a polymerase chain reaction (PCR)-based method. Droplet digital PCR (ddPCR) is a novel PCR technique which is sensitive and precise in quantifying DNA templates of the test samples. In this study, we developed a ddPCR assay to detect and quantify P. allius in soil. The specificity and sensitivity of the assay was first determined using P. allius nematode DNA or DNA from sterilized soil artificially inoculated with P. allius, and the assay was used to quantify P. allius populations in field soils. The assay did not detect nematodes other than P. allius, thus showing high specificity. It was able to detect P. allius equivalent to a 0.01 and 0.02 portion of a single nematode in soil DNA and nematode DNA extracts, respectively. Highly linear relationships between DNA copy numbers from ddPCR and serial dilutions of known concentrations were observed with DNA from P. allius nematodes (R2 = 0.9842) and from artificially infested soil (R2 = 0.9464). The P. allius populations from field soils determined by ddPCR were highly correlated with traditional microscopic counts (R2 = 0.7963). To our knowledge, this is the first report of applying ddPCR to detect and quantify stubby root nematode in soil. The results of this study support the potentiality of a ddPCR assay as a new research tool in diagnostics of plant-parasitic nematodes.

A novel chorismate mutase effector secreted from root-knot nematode Meloidogyne enterolobii manipulates plant immunity to promote parasitism1

Meloidogyne spp. is an economically important plant-parasitic nematode distributed worldwide. To fight with host immune system for successful parasitism, plant parasitic nematodes secrete effectors to promote infection. In this study, we identified one chorismate mutase (CM) effector from M. enterolobii, named Me-CM. Spatial and temporal expression assays exhibited Me-cm is expressed in esophageal glands and up-regulated at parasitic-stage juveniles. Me-CM affects the pathogenicity of M. enterolobii based on the reduced infection rate, number of galls, egg masses, eggs per mass and multiplication rate collected from RNA silencing experiments. We showed that Me-CM localized in the cytoplasm and nucleus of plant cells and decreased the expression level of the marker gene PR1 of salicylic acid (SA) pathway. Besides, constitutive expression of Me-cm in Arabidopsis thaliana significantly reduced salicylic acid concentration. These results suggested that M. enterolobii may secrete effector Me-CM to fight with plant immune systems via regulating SA signaling pathway when interacting with host plants, ultimately facilitating parasitism.

Molecular diagnosis and differentiation of Meloidogyne arenaria, Meloidogyne javanica and Meloidogyne incognita using SNP-based KASP assays

Root-knot nematodes (RKNs) are one of the most economically important plant-parasitic nematodes in many crops. Meloidogyne arenaria, M. incognita and M. javanica are the most common species attacking tomato, pepper, eggplant, cucumber, melon, watermelon and zucchini, which have economic importance in vegetable growing areas. Thus, a rapid and accurate identification system is required for RKNs. In this study, Kompetitive Allele-Specific PCR (KASP) genotyping assays were developed to identify three common RKNs. The novel technique developed in this study utilized only two primers: one allele-specific forward primer and a reverse common primer. Meloidogyne arenaria, M. incognita and M. javanica were separated easily from each other and other RKN species. This is the first report on three species identified by the KASP assay. The results showed that the KASP assays are suitable for the high-throughput identification of these species. The developed system can be used to identify three RKN species in research, routine and quarantine laboratories.

Exploration of rhizosphere-dwelling nematophagous Trichoderma spp. using novel ‘bait technique’ with root-knot nematode Meloidogyne incognita

Throughout the world Trichoderma spp. are majorly used as biocontrol agents for managing the economically important plant-parasitic nematodes. We employed a novel strategy to investigate the variety of rhizosphere dwelling Trichoderma species using the nematode Meloidogyne incognita as prey bait. Nine nematophagous Trichoderma spp., validated morphologically and molecularly, were discovered during the expedition in several agroclimatic zones of India. Molecular phylogenetic analysis of these species along with the reported Trichoderma spp. from ‘Harzianum clade’ from India indicated the true identity of Indian T. harzianum sensu stricto to be disputed. Nematophagous nature of the isolated species was confirmed through the presence of extracellular lytic enzymes, secondary metabolites, volatile organic compounds, Huperzine A, and tri-gene cluster variability. Besides, the most promising T. yunnanense isolate, shortlisted based on its in vitro potential against M. incognita, showed the highest levels of nematode parasitism, egg hatching inhibition and juvenile mortality compared to all other isolates and species. Expression of green fluorescent protein in T. yunnanense helped tracking its infection in the juveniles and further validated the nematode parasitizing capacity. The chosen isolate decreased the multiplication factor of M. incognita in pot culture assays and in organically produced capsicum in nematode-infected sick soil. It is interesting that the isolate also markedly increased the plant growth and yield, which was a bonus. Therefore, the performance of T. yunnanense demonstrated through various strategies instills high confidence to propose it as a prospective species for developing as commercially potent nematode biocontrol agent.

Phytonematode Diversity in Tomato Crops of Chittoor District, Andhra Pradesh, India: A Comprehensive Survey, Distribution, and Community Analysis

The present study was undertaken to analyze the distribution and community analysis of important plant parasitic nematodes associated with the vegetable crop tomato in Chittoor District of Andhra Pradesh. The study revealed that maximum infestation is observed in somala mandal and least in Chowdepalle mandals of Chittoor District of Andhra Pradesh. Plant parasitic nematodes viz., Meloidogyne incognita, Hoplolaimus spp., and Tylenchorynchus spp. etc. was found to be associated with tomato crops. It has been observed that M. incognita population was found to be maximum in tomato crops at Chittoor Districts of Andhra pradesh. The prominence value was found to be maximum for root knot nematode in tomato crops having 8.76/200 cc. The data also revealed that M. incognita absolute frequency in tomato was 100% and absolute density is around 87.60% while the genera Hoplolaimus showed the least occurrence frequency of 40% and absolute density of 1.56%. From these studies it can be interpreted that M. incognita is most predominant nematode and cause damage substantially to tomato crop grown in Chittoor District of Andhra Pradesh.

Plant parasitic nematodes associated with oil palm trees in three regions of Ghana

Field surveys were conducted in three oil palm producing regions of Ghana to determine the frequency, population density and geographical distribution of plant parasitic nematodes associated with oil palm. Palms ranging from 4 to 12 years were surveyed during the peak periods of two successive cropping seasons of 2019 and 2020. A total of 64 soil and root samples were collected and plant parasitic nematodes extracted and identified from them. 716 mixed populations of 11 economically important plant-parasitic nematode genera were recovered and identified from both roots and soils during the period. These were Aphelenchus, Criconemoides, Helicotylenchus, Hemicriconemoides, Meloidogyne, Pratylenchus, Radopholus, Rotylenchus, Tylenchorynchus, Tylenchus and Xiphinema. Meloidogyne and Pratylenchus were the most frequently isolated and widely distributed geographically. Meloidogyne recovered from both soil and roots were 220 whilst Pratylenchus recovered were 129. These nematodes are very important pests of several crops, therefore, if not managed properly, could pose a threat to oil palm production in Ghana.

An Insight into Occurrence, Biology, and Pathogenesis of Rice Root-Knot Nematode Meloidogyne graminicola.

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.

Occurrence and Distribution of Root-Knot Nematodes in Kiwifruit Orchard

The study was conducted to investigate the infestation and distribution of plant-parasitic nematodes on kiwi orchards in Korea. Plant parasitic nematodes genus and densities were investigated at a total of 102 sites in Jeollanam-do, Gyeongsangnam-do, and Jeju-do, which are the main production areas of domestic kiwi orchards. Plant parasitic nematodes detected were of 9 genera, including root-knot nematodes (Meloidogyne spp.), spiral nematodes (Helicotylenchus spp.), and needle nematodes (Paratylenchus spp.), and 56% of the 102 plantations were infected with root-knot nematodes. Root-knot nematodes were found to be the most important plant parasitic nematode in domestic kiwi orchards. The average density of root-knot nematodes is 97 per 300 cm&lt;sup&gt;3&lt;/sup&gt; soil, and there is concern about the kiwi yield reduction. As a result of identifying the root-knot nematode species: M. arenaria, M. hapla, M. incognita, and M. javanica. Among them, M. arenaria is the most dominant. As the plant parasitic nematode infection route in fruit trees is often spread through the transplantation of infected seedlings, attention should be paid to the production of nematode-free plants during the production and supply of kiwifruit plants.

Biological Management of Root Knot Nematode, Meloidogyne incognita through Bacterial Antagonists Infecting Tomato

Root-knot nematodes have wide host range, causing damage to many annual and perennial crops. More than 100 species of Meloidogyne are known in which Meloidogyne incognita (Kofoid and White) Chitwood is one of the most common and important plant parasitic nematode in tropical and subtropical regions of the world including Pakistan. This study was planned to investigate the interaction of Plant Growth Promoting Rhizobacteria and Pasteuria penetrans for the management of root knot nematode M. incognita on tomato in green house at 30 + 4 0C. Earthen pots 20 cm dia. having sterilized soil was mixed with Pasteuria penetrans root powder @ 103 spores per gm of soil. Three week old seedlings of tomato Money Maker were transplanted singly in pots. One week after transplanting, 30 ml of bacterial (Bacillus subtilis, Pseudomonas fluorescens and Enterobacter cloacae) suspension were applied in root zone. Seven days after application of PGPR, 2000 J2 were applied at root zone. The experiment was arranged in Completely Randomized Design and six treatments were replicated tenfold. Pasteuria penetrans alone or in different combinations with PGPR were applied. Pots with nematode and without PGPR, Pp and nematode were kept as control. Sixty days after nematode application, plants were harvested carefully. Data were recorded on plant growth parameters and nematode reproduction in terms of number of egg mass, number of females, number of galls and galling index (0-10). The plant treated with Enterobacter cloacae + Pp significantly suppressed the number of egg mass 69.38%, number of galls 68%, number of females 66.21% and galling index 56.82% compared to control resulting in improved growth over control. The treatments B. subtilis + Pp and P. fluorescens + Pp showed intermediary effect on both nematode reproduction and plant growth..Pasteuria penetrans was least observed effective in suppressing number of egg mass 57.53 %, number of females 55%, number of galls 55.73% and galling index 47.73%.

Evaluation of Nematicidal Potential of Plant Growth Promoting Rhizobacteria against Meloidogyne incognita

Root-knot nematodes have a wide host range, causing damage to many annual and perennial crops. More than 100 species of Meloidogyne are known in which M. incognita (Kofoid and White) Chitwood is one of the most common and important plant parasitic nematode in tropical and subtropical regions of the world including Pakistan. Therefore, the present study was planned to check the effect of PGPRs on juvenile mortality and egg hatching inhibition of M. incognita under lab conditions. Eggs were isolated from egg masses by using NaOCl solution. Rhizobacteria (Bacillus subtilis, Pseudomonas fluorescens, Azotobacter chroococcum, Azospirillum sp., Rhizobium leguminosarum) were multiplied on nutrient broth and kept overnight at 28 ± 2 °C in shaking incubator. Cell free culture filtrates were obtained in falcon tubes by centrifuging PGPRs @ 4000 RPM twice for 30 minutes. Two ml of toxins of each PGPR was poured into each 5cm-dia. petri plate and 100 microliters of egg suspension containing approximately 100 eggs were put in each petri plate. Similar experimental conditions and protocols were used for juveniles’ mortality. In this experiment, instead of eggs, 100 J2s contained in 100 microliters of juvenile suspension were put in each petri plate. The petri plates were placed in completely randomized design in incubator at 28 ± 2 °C with ten replicates. Petri dishes containing distilled water were kept under control. All the PGPRs caused larval mortality and inhibition in egg hatching with varying degrees. The maximum egg hatching was inhibited by Bacillus subtilis while Rhizobium leguminosarum was found the least effective. The other PGPRs i.e. Pseudomonas fluorescens, Azotobacter chroococcum, and Azospirillum sp. showed intermediate results.

Biocontrol efficacy of Bacillus velezensis strain YS-AT-DS1 against the root-knot nematode Meloidogyne incognita in tomato plants.

Root-knot nematodes (RKNs; Meloidogyne spp.), one of the most economically important plant-parasitic nematodes (PPNs), cause severe yield and quality losses in agriculture annually. The application of biological control agents is an environmentally safe and effective approach to control RKNs. Here, we report the genomic characteristics of a Bacillus velezensis strain YS-AT-DS1 (Bv-DS1) isolated from the tidal soil, revealing that it has a 4.73 Mb circular chromosome with an average GC-content of 46.43%, 3,977 genes, 86 tRNAs, and 27 rRNAs, and contains secondary metabolite clusters for producing antimicrobial compounds. In vitro assays indicated that Bv-DS1 has not only antagonistic activities against fungal pathogens, but also shows nematicidal activity, with a mortality rate of 71.62% mortality rates in second-stage juvenile (J2s) Meloidogyne incognita. We then focused on the biocontrol efficiency of Bv-DS1 against M. incognita in pot assays. Preinoculation with Bv-DS1 enhanced tomato growth, and significantly reduced the infection rate of J2s, and the number of galls and egg masses on tomato roots. The underlying mechanism in Bv-DS1-induced resistance to M. incognita was further investigated through split-root experiments, and analysing the expression of the genes related to jasmonic acid (JA), salicylic acid (SA), and the tonoplast intrinsic protein (TIP). The results indicated that Bv-DS1 could not activate host systemic-induced resistance (ISR) in the split-root system of tomatoes. Additionally, the expression of JA- (LOX D and MC) and SA- (PAL2 and PR) responsive genes did not change in Bv-DS1-pretreated plants at 3 and 14 days after nematode inoculation. The presented data showed that JA-and SA-dependent pathways were not required for the biocontrol action of the Bv-DS1 against RKN. The TIP genes, responsible for transport of water and small substrates in plants, have previously been shown to negatively regulate the parasitism of PPNs. Surprisingly, Bv-DS1 compromised the downregulation of TIP1.1 and TIP1.3 by M. incognita. Together, our data suggest that Bv-DS1 exhibits a dual effect on plant growth promotion and protection against RKN, possibly related to the regulation of water and solute transport via TIPs. Thus, the Bv-DS1 strain could be used as a biocontrol agent for RKN control in sustainable agriculture.

The Fight against Plant-Parasitic Nematodes: Current Status of Bacterial and Fungal Biocontrol Agents.

Plant-parasitic nematodes (PPNs) are among the most notorious and underrated threats to food security and plant health worldwide, compromising crop yields and causing billions of dollars of losses annually. Chemical control strategies rely heavily on synthetic chemical nematicides to reduce PPN population densities, but their use is being progressively restricted due to environmental and human health concerns, so alternative control methods are urgently needed. Here, we review the potential of bacterial and fungal agents to suppress the most important PPNs, namely Aphelenchoides besseyi, Bursaphelenchus xylophilus, Ditylenchus dipsaci, Globodera spp., Heterodera spp., Meloidogyne spp., Nacobbus aberrans, Pratylenchus spp., Radopholus similis, Rotylenchulus reniformis, and Xiphinema index.