Harnessing nature's arsenal: Ochrobactrum bacteria metabolites in the battle against root- knot nematode - Insights from in vitro and molecular docking studies.

Agricultural Productivity and plant health are threatened by the root-knot nematode. The use of biocontrol agents reduces the need for chemical nematicides and improves the general health of agricultural ecosystems by offering a more environmentally friendly and sustainable method of managing nematode infestations. Plant-parasitic nematodes can be efficiently managed with the use of entomopathogenic nematodes (EPNs), which are widely used biocontrol agents. This study focused on the nematicidal activity of the secondary metabolites present in the bacteria Ochrobactrum sp. identified in the EPN, Heterorhabditisindica against Root-Knot Nematode (Meloidogyne incognita). Its effect on egg hatching and survival of juveniles of root- knot nematode (RKN) was examined. The ethyl acetate component of the cell-free culture (CFC) filtrate of the Ochrobactrum sp. bacteria was tested at four different concentrations (25 %, 50 %, 75 % and 100 %) along with broth and distilled water as control. The bioactive compounds of Ochrobactrum sp. bacteria showed the highest suppression of M. incognita egg hatching (100 %) and juvenile mortality (100 %) at 100 % concentration within 24 h of incubation. In this study, unique metabolite compounds were identified through the Gas Chromatography- Mass Spectrometry (GC-MS) analysis, which were found to have anti- nematicidal activity. In light of this, molecular docking studies were conducted to determine the impact of biomolecules from Ochrobactrum sp. using significant proteins of M. incognita, such as calreticulin, sterol carrier protein 2, flavin-containing monooxygenase, pectate lyase, candidate secreted effector, oesophageal gland cell secretory protein and venom allergen-like protein. The results also showed that the biomolecules from Ochrobactrum sp. had a significant inhibitory effect on the different protein targets of M. incognita. 3-Epimacronine and Heraclenin were found to inhibit most of the chosen target protein. Among the targets, the docking analysis revealed that Heraclenin exhibited the highest binding affinity of -8.6 Kcal/mol with the target flavin- containing monooxygenase. Further, the in vitro evaluation of 3- Epimacronine confirmed their nematicidal activity against M. incognita at different concentrations. In light of this, the present study has raised awareness of the unique biomolecules of the bacterial symbiont Ochrobactrum sp. isolated from H. indica that have nematicidal properties.

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 ß-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.