Bacillusvelezensis Strains for Protecting Cucumber Plants from Root-Knot Nematode Meloidogyne incognita in a Greenhouse

Metagenomic profiling of tomato rhizosphere delineates the diverse nature of uncultured microbes as influenced by Bacillus velezensis VB7 and Trichoderma koningiopsis TK towards the suppression of root-knot nematode under field conditions

The plant-parasitic Root Knot Nematodes (Meloidogyne spp.,) play a pivotal role to devastate vegetable crops across the globe. Considering the significance of plant-microbe interaction in the suppression of Root Knot Nematode, we investigated the diversity of microbiome associated with bioagents-treated and nematode-infected rhizosphere soil samples through metagenomics approach. The wide variety of organisms spread across different ecosystems showed the highest average abundance within each taxonomic level. In the rhizosphere, Proteobacteria, Firmicutes, and Actinobacteria were the dominant bacterial taxa, while Ascomycota, Basidiomycota, and Mucoromycota were prevalent among the fungal taxa. Regardless of the specific treatments, bacterial genera like Bacillus, Sphingomonas, and Pseudomonas were consistently found in high abundance. Shannon diversity index vividly ensured that, bacterial communities were maximum in B. velezensis VB7-treated soil (1.4-2.4), followed by Root Knot Nematode-associated soils (1.3-2.2), whereas richness was higher with Trichoderma konigiopsis TK drenched soils (1.3-2.0). The predominant occurrence of fungal genera such as Aspergillus Epicoccum, Choanephora, Alternaria and Thanatephorus habituate rhizosphere soils. Shannon index expressed the abundant richness of fungal species in treated samples (1.04-0.90). Further, refraction and species diversity curve also depicted a significant increase with maximum diversity of fungal species in B. velezensis VB7-treated soil than T. koningiopsis and nematode-infested soil. In field trial, bioagents-treated tomato plant (60% reduction of Meloidogyne incognita infection) had reduced gall index along with enhanced plant growth and increased fruit yield in comparison with the untreated plant. Hence, B. velezensis VB7 and T. koingiopsis can be well explored as an antinemic bioagents against RKN.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03851-1.

Novel Genes and Key Signaling Molecules Involved in the Repulsive Response of Meloidogyne incognita against Biocontrol Bacteria

The ability of the model organism, Caenorhabditis elegans, to distinguish and escape from pathogenic bacteria has been extensively studied; however, studies on the repulsive response of Meloidogyne incognita are still in their infancy. We have recently demonstrated that biocontrol bacteria induce a repulsive response in M. incognita via two classical signaling pathways. The present study aimed to identify the novel genes and signaling molecules of M. incognita that potentially contribute to its defense reaction. Analysis of the transcriptome data of M. incognita with and without a repulsive response against Bacillus nematocida B16 obtained 15 candidate genes, of which the novel genes Minc3s01748g26034 and Minc3s02548g30585 were found to regulate the aversive behavior of M. incognita, and their functions were further validated. To further confirm the neuronal localization of the two novel genes in M. incognita, in situ hybridization was conducted using the digoxin-labeled probes of ten tag genes, and preferentially profiled the localization of amphid sensory neurons of M. incognita. Analysis of the overviewed neuronal map suggested that Minc3s01748g26034 and Minc3s02548g30585 functioned in ASK/ASI and CEPD/V neurons, respectively. During their interactions, the volatile compounds 3-methyl-butyric acid and 2-methyl-butyric acid produced by the biocontrol bacteria were predicted as the primary signaling molecules that promoted the repulsive behavior of M. incognita against biocontrol bacteria. The findings provided novel insights into the mechanisms underlying the repulsive response of M. incognita that are different from the canonical molecular pathways previously found in C. elegans and can aid in developing novel strategies for controlling root-knot nematodes.

Interfacial Polymerization Depth Mediated by the Shuttle Effect Regulating the Application Performance of Pesticide-Loaded Microcapsules

The highly water-soluble nematicide fosthiazate is anticipated to undergo microencapsulation in order to enhance its retention around plant roots and mitigate leaching into groundwater. However, the underlying mechanism governing the influence of hydrophilicity of the microcapsule (MC) core on the evolution of the microcapsule shell remains unclear, posing challenges for encapsulating water-soluble core materials. This study elucidates the microlevel formation mechanism of microcapsules by investigating the impact of interfacial mass transfer on shell formation and proposes a method for regulating the structure of shells. The study reveals that enhancing the hydrophilicity of the core enhances the shuttle effect between the oil and aqueous phase, expands the region of polymerization reactions, and forms a loose and thick shell. The thickness of the microcapsule shell prepared using solvent oil 150# (MCs-SOL) measures only 264 nm, while that of the microcapsules prepared using propylene glycol diacetate and solvent oil 150# at a ratio of 2:1 (MCs-P2S1) is 5.2 times greater. The enhanced compactness of the shell reduced the release rate of microcapsules and the leaching distance of fosthiazate in soil, thereby mitigating the risk of leaching loss and facilitating the distribution of active ingredients within crop roots. The MCs-SOL had a limited leaching distance measurement of 8 cm and exhibited a satisfactory efficacy of 87.3% in controlling root galling nematodes. The thickness and compactness of the MCs shell can be regulated by manipulating the interfacial shuttle effect, providing a promising approach to enhancing utilization efficiency while mitigating potential environmental risks.

Primary Screening of Microorganisms against Meloidogyne hapla (Chitwood, 1949) under the Conditions of Laboratory and Vegetative Tests on Tomato

Highly adapted obligate endoparasites of the root system, root-knot nematodes (Meloidogyne spp.), cause great damage to agricultural crops. Our research is aimed at the assessment of nematicidal activity and effectiveness of antagonist fungal and bacterial strains against the most common type of root-knot nematode in the south of Russia. By means of molecular genetic identification, it was found that in the south of Russia, the species Meloidogyne hapla Chitwood, 1949 and Meloidogyne incognita (Kofoid and White, 1919) Chitwood, 1949 cause galls on the roots of open-ground and greenhouse tomato. Screening of microbial agents against second-stage juvenile (J2) M. hapla was carried out in the laboratory. At the end of the experiment, two liquid fungal cultures of Paecilomyces lilacinus BK-6 and Metarhizium anisopliae BK-2 were isolated, the nematicidal activity of which reached 100.0 and 70.2%, and exceeded the values of the biological standard (Nemotafagin-Mikopro) by 38.4% and 8.8%. The highest biological efficacy was noted in the liquid cultures of P. lilacinus BK-6, M. anisopliae BK-2, and Arthrobotrys conoides BK-8 when introduced into the soil before planting tomato. The number of formed galls on the roots was lower in comparison with the control by 81.0%, 75.5%, and 74.4%.

Biocontrol of Plant Diseases by Means of Antagonist Microorganisms, Biostimulants and Induced Resistance as Alternatives to Chemicals

Plant diseases are one of the biggest problems in conventional agriculture as they reduce both yield and crop value [...].

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.