Phytonematodes are globally important functional components of the belowground ecology in both natural and agricultural soils; they are a diverse group of which some species are economically important pests, and environmentally benign control strategies are being sought to control them. Using eco-evolutionary theory, we test the hypothesis that root-exudates of host plants will increase the ability of a hyperparasitic bacteria, Pasteuria penetrans and other closely related bacteria, to infect their homologous pest nematodes, whereas non-host root exudates will not. Plant root-exudates from good hosts, poor hosts and non-hosts were characterized by gas chromatography-mass spectrometry (GC/MS) and we explore their interaction on the attachment of the hyperparasitic bacterial endospores to homologous and heterologous pest nematode cuticles. Although GC/MS did not identify any individual compounds as responsible for changes in cuticle susceptibility to endospore adhesion, standardized spore binding assays showed that Pasteuria endospore adhesion decreased with nematode age, and that infective juveniles pre-treated with homologous host root-exudates reduced the aging process and increased attachment of endospores to the nematode cuticle, whereas non-host root-exudates did not. We develop a working model in which plant root exudates manipulate the nematode cuticle aging process, and thereby, through increased bacterial endospore attachment, increase bacterial infection of pest nematodes. This we suggest would lead to a reduction of plant-parasitic nematode burden on the roots and increases plant fitness. Therefore, by the judicious manipulation of environmental factors produced by the plant root and by careful crop rotation this knowledge can help in the development of environmentally benign control strategies.

Background: Virulence of the entomopathogenic nematode, Heterorhabditis indica against larvae (3rd, 4th and 5th larval instars) and pupae of citrus fruit piercing moth, Eudocima materna L. (Lepidoptera: Erebidae) was evaluated under laboratory conditions. The experiments included pathogenicity assessment of H. indica against larvae and pupae using a range of concentrations (10, 25, 50, 100 and 200 infective juveniles (IJs) larva⁻¹ and pupa⁻¹) as well as evaluation of their reproductive potential on different larval instars with different concentrations (50, 100, 200, 400 and 600 IJs larva⁻¹). Results: Application of increasing concentrations of IJs induced higher mortality on larval instars and pupae with mean mortality ranging from 26.6 to 100% (LC₅₀- 3rd (14.43 IJs larva⁻¹), 4th (17.08 IJs larva⁻¹), 5th (23.63 IJs larva⁻¹)) and 10–70% (LC₅₀- 85.91 IJs pupa⁻¹) after 48 h post-exposure, respectively. H. indica successfully reproduced in the 3rd, 4th and 5th larval instars of E. materna and their offspring emerged from the cadavers. The highest reproduction was recorded in 5th instar larvae (1,082,855 IJs larva⁻¹) at 600 IJs larva⁻¹ in E. materna. Conclusion: The present study suggests that H. indica strain had the potential for biological control of E. materna.

A comprehensive study was conducted to assess the diversity and community analysis of plant parasitic nematodes (PPN) in the rhizosphere soil of Assam lemon orchards across four districts in Assam. The study identified six predominant PPN genera: Tylenchulus semipenetrans, Helicotylenchus sp., Hoplolaimus sp., Tylenchorhynchus sp., Pratylenchus sp. and Rotylenchulus sp. The nematode community structure was analyzed using various ecological parameters. Among the identified PPN, T. semipenetrans and Helicotylenchus sp. were the most abundant (100%), followed by Hoplolaimus sp. (80%), Tylenchorhynchus sp. (60%) and Pratylenchus sp. (60%). This identification of PPN genera associated with Assam lemon orchards provides essential information for developing effective nematode management strategies aimed at reducing yield losses and enhancing food security.