Tylenchulus semipenetrans is a soil-borne pathogen that causes substantial damage and economic losses to citrus crops worldwide. Due to the high toxicity of chemical nematicides to humans and the environment, biocontrol bacteria have emerged as a promising alternative for managing citrus nematodes. This study aimed to screen bacterial strains for their efficacy to control T. semipenetrans and assess their impact on citrus plant growth. A total of 107 bacterial strains were isolated from the soil and roots of infested citrus trees. Among these, five strains exhibited significant nematicidal activity against T. semipenetrans. Four bacterial densities were tested for each strain: 3.6 x 10(5), 2.5 x 10(4), 3.6 x 10(3), and 1.2 x 10(3) cells/ml. These strains were tested both individually and in combination to evaluate their efficacy. The five strains were identified as Variovorax paradoxus, Bacillus pseudomycoides, Bacillus simplex, Bacillus cereus, and Paracoccus speluncae based on physiological, biochemical, and molecular (16S rRNA gene sequences) analyses. Juvenile mortality (J2s) and egg hatching inhibition were positively correlated with bacterial concentration and exposure duration. The highest juvenile mortality (100%) was observed with a combination of all five bacteria (3.6 x 10(5) cells/ml) after 96 h, while B. cereus alone achieved 98.98% mortality. The maximum nematicidal activities of the bacterial filtrates were generally observed between the 4th and 6th days of incubation, coinciding with peak bacterial growth and biomass production. The selected isolates also demonstrated the ability to produce indole acetic acid and solubilize phosphorus. In greenhouse experiments, the five isolates reduced T. semipenetrans populations by up to 62.96% compared to the control. Additionally, all rhizosphere bacteria and their combination significantly enhanced plant growth parameters (p < 0.0001). Notably, P. speluncae BR21 has not previously been tested for nematicidal effects on any nematode, making this the first documented report of its nematicidal potential.

This study investigated the infestation of tomato plants by the plant-parasitic nematode, M. incognita, and its accurate detection by plant electrophysiology (PE). Dedicated tests were done on whole plants to record electrophysiological signals from nematode infested and uninfested plants and to establish a trained model indicating nematode-induced stress. Monitoring nematode-induced stress by PE confirmed the results obtained by assessing root galls and quantifying xylem sap 3 to 4 weeks after infestation. The machine learning model captured the stress intensities and the time course of plant damage caused by nematodes. Stress caused by second-stage juveniles (J2) infestation appeared 3 to 5 days after infestation (DAI), whereas stress caused by egg infestation was detected 5 to 7 days later (10-13 DAI). For the first time, the real-time effectiveness of nematicides was recorded in further tests. Nematode infested plants treated preventatively with cyclobutrifluram (TYMIRIUM (R) technology) showed a delayed and short (about 3 days) period of low stress intensity, whereas infested but untreated plants showed a period of maximum stress for about 12 days. In addition, depending on the type of application (preventative or curative), different modes of biological activity of IRAC group N-2 and N-3 nematicides (fluopyram, abamectin) could be captured by PE signalling. PE offers a new way of monitoring plant health in real time, which is particularly valuable for accessing 'invisible' pests, such as plant-parasitic nematodes in the soil.

Root-knot nematode (RKN) (Meloidogyne incognita) is a major plant parasitic nematode that severely damages crops, leading to significant yield losses and substantial economic impact globally. This study aims to investigate an environmentally sustainable biological strategy for mitigating parasitic populations of the root-knot nematode, M. incognita. Specifically, the research focuses on assessing the nematicidal efficacy of Acalypha indica against M. incognita mortality and second-stage juveniles' (J2) hatching under controlled in vitro conditions. A. indica leaf aqueous extract was applied at varying concentrations (250, 500, 750, and 1000 ppm) to J2s and egg masses of M. incognita. Notably, at 1000 ppm, a significant increase in J2 mortality and hatching inhibition was observed, while 250 ppm concentration showed the least favorable outcome; with mortality rates ranging from 22-82%. Chemical analysis via gas chromatography-mass spectroscopy (GC-MS) identified Benzoic acid, Cyclooctasiloxane, and 3-Isopropoxy-1,1,1,7,7,7-hexamethyl-3,5,5-tris (trimethylsiloxy) tetrasiloxane as predominant compounds. The nematicidal activity of A. indica leaf extract was further validated through in silico molecular docking, revealing that benzoic acid, Cyclooctasiloxane, and 3-Isopropoxy-1,1,1,7,7,7-hexamethyl-3,5,5-tris (trimethylsiloxy) tetrasiloxane bind to the ODR 3 protein of M. incognita with binding energies of -15.72, -8.91, and -7.35 kJ/mol, respectively. These findings hold promise for environmentally benign root-knot nematode management, contributing to improved soil health.

This study investigates the efficacy of Trichoderma spp. and Bacillus spp., as well as their gamma radiation-induced mutants, as potential biological control agents against Meloidogyne javanica (Mj) in tomato plants. The research encompasses in vitro assays, greenhouse trials, and molecular identification methodologies to comprehensively evaluate the biocontrol potential of these agents. In vitro assessments reveal significant nematicidal activity, with Bacillus spp. demonstrating notable effectiveness in inhibiting nematode egg hatching (16-45%) and inducing second-stage juvenile (J2) mortality (30-46%). Greenhouse trials further confirm the efficacy of mutant isolates, particularly when combined with chitosan, in reducing nematode-induced damage to tomato plants. The combination of mutant isolates with chitosan reduces the reproduction factor (RF) of root-knot nematodes by 94%. By optimizing soil infection conditions with nematodes and modifying the application of the effective compound, the RF of nematodes decreases by 65-76%. Molecular identification identifies B. velezensis and T. harzianum as promising candidates, exhibiting significant nematicidal activity. Overall, the study underscores the potential of combined biocontrol approaches for nematode management in agricultural settings. However, further research is essential to evaluate practical applications and long-term efficacy. These findings contribute to the development of sustainable alternatives to chemical nematicides, with potential implications for agricultural practices and crop protection strategies.

The dynamic of plant-parasitic nematode populations in soil is closely related to soil microorganisms. Fungi from Heterodera zeae cysts were isolated to explore the phenomenon of decline in the H. zeae population in the soil. Phylogenetic study of partial ITS, BenA, CaM, and RPB2 gene sequences, in addition to morphological investigations, was utilized to identify a nematode-destroying fungus. The nematicidal activity of a novel strain GX1 against H. zeae was assessed in vitro and in the greenhouse. Our findings revealed that strain GX1 is a new species of Talaromyces, named Talaromyces cystophila. It has a strong parasitic and lethal effect on H. zeae cysts, with 91.11% parasitism on cysts at 3 days after treatment. The contents of second-stage juveniles (J2s) and eggs inside the cysts were degraded and formed dense vacuoles, and the damaged eggs could not hatch normally. The spore suspension exhibited high nematophagous activity against nematodes, and fermentation filtrate exhibited marked inhibition of egg hatching and nematicidal activities on J2s. The hatching inhibition rates of eggs exposed to 1 x 10(8) CFU/ml spore suspensions or 20% 1-week fermentation filtrate (1-WF) for 15 days were 98.56 and 100%, respectively. The mortality of J2s exposed to 1 x 10(8) CFU/ml spore suspension reached 100% at 24 h; exposure to 50% 2-WF was 98.65 and 100% at 24 and 48 h, respectively. Greenhouse experiments revealed that the spore suspension and fermentation broth considerably decreased H. zeae reproduction by 56.17 to 78.76%. T. cystophila is a potential biocontrol strain with nematophagous and nematicidal activity that deserves attention and application.