An investigation on the interactions between entomopathogenic nematodes and plant growth promoting bacteria

Abstract

Increasing demands on global food production have resulted in the overuse of chemical fertilisers and pesticides, leading to an increase in environmental pollution and pest resistance. Traditional fertiliser applications are carried out to supplement soil with a bioavailable form of nutrients essential for plant growth, and pesticides are applied to prevent crop damage from economically detrimental pests. The adverse impacts of these conventional agricultural practices include water, air and soil pollution in addition to direct negative effects on human health. There is growing public and political concern on these issues and if current intensive practices are continued, natural resources including clean water, fertile soil, and biodiversity, in flora and fauna, are under severe threat for future generations. In order to facilitate the transition away from the use of conventional agri-chemicals and prevent further environmental pollution, research, and resulting application, must focus on the use of naturally occurring biofertilisers and the biological control of economically important pests. This study was the first of its kind and examined the basic fundamental interactions between entomopathogenic nematodes (EPN; Rhabditida: Heterorhabditis and Steinernema) and plant growth promoting (PGP) bacteria in order to provide a framework for the development of an environmentally sustainable, reliable, cost-effective, multi-function product for biocontrol and PGP. A comprehensive examination on the effects of PGP bacteria on EPN showed that these naturally occurring soil organisms did not significantly affect EPN survival, infectivity, virulence, attraction to their host or reproduction. Major findings of this work include Greenhouse results which revealed that a combination of Heterorhabditis bacteriophora and the PGP bacteria Pseudomonas fluorescens F113 gfp and P. fluorescens L321 gfp individually contributed significantly to an increase in oilseed rape (Brassica napus) fresh weight. Laboratory-based bioassay results showed that P. fluorescens F113 gfp successfully colonised infective juveniles (IJ) of Steinernema feltiae SB 12(1) and H. bacteriophora. Moreover, there appears to be some level of interaction between P. fluorescens F113 gfp and EPN and their associated endosymbionts (Xenorhabdus bovienii and Photorhabdus luminescens) as P. fluorescens F113 gfp survived inside Galleria mellonella following nematode infection and insect mortality. Interactions between EPN and bacterial species and strains varied. However, the overall results are positive and indicate that the EPN and PGP bacteria examined here are compatible and show promising potential to be developed and formulated as a combined agricultural product, for insect control and increased soil and plant health.