Rhizophere engineering with beneficial microbes for growth enhancement and nematode disease complex management in gherkin (Cucumis anguria L.)

Abstract

Major studies on root knot nematode (Meloidogyne incognita) tend to focus on the nematode alone, but with not much attention to its synergistic association with bacterial or fungal pathogens co-inhabiting the crop rhizosphere. Nematodes pave the way for easy entry of these pathogens inside the host roots, forming a disease complex that causes enormous yield loss. Greater knowledge on the interaction of fungal and nematode pathogens is required to find better solutions for sustainable management of the nematode diseases complex. Hence, this research was designed to study the interaction between M. incognita and Fusarium oxysporum f. sp. melonis and evaluate the consortia formulation of biocontrol agents (BCA) Trichoderma viride IIHR TV-2 and Bacillus subtilis IIHR BS-21 against nematode-fungal diseases complex in gherkin (cv. Ajax). Nematode-fungus interaction studies revealed that inoculation of M. incognita 15 days earlier to fungus showed maximum wilt incidence (96.81%) than fungus alone (85.29%), revealing their synergistic association. Under in vitro, cell free culture filtrates of T. viride IIHR TV-2 and B. subtilis IIHR BS-21 showed significant antagonism ovicidal, larvicidal and fungicidal action. Both the BCA strains were found compatible with each other (91.84%). Under field conditions, seed treatment (20 ml kg−1) and subsequent soil application of vermicompost (2 t ha−1) enriched with BCA consortia (5 l) before planting, followed by monthly application at 1 t ha−1 showed maximum increase in the plant growth parameters and reduction in nematode population in soil (66.37%), roots (62.45%) and per cent wilt incidence (42.56%) compared to untreated plants. Marketable gherkin yields also increased by 34.42% over the control. These results emphasize the efficacy of vermicompost enriched with microbial consortia in managing pathogen complexes and can be included as promising component in integrated nematode and disease management for gherkin and other horticultural crops.