Pseudomonas protegens as a stand-alone bacterial biocontrol agent or in association with EPNs

Abstract: The bioinsecticidal potential of Pseudomonas protegens is known against diverstarget pests, and its usefulness as a biological control agent also leverages the ability to act as plant growth promoter and a phytopathogen antagonist. This bacterium appears to be able to act by ingestion against insect hosts, crossing gut barriers and eventually causing bacterisepticaemia. Several bacterial target genes, including chitinases and fitD toxin, are involved in a mode of action that appears to be complex and multifactorial. As a soil-dwelling naturabiopesticide supporting plant health, P. protegens has occasionally been found in association with entomopathogenic nematodes. In this study we have investigated the potential of a neP. protegens strain isolated from Steinernema IJs both as a stand-alone biocontrol agent and aa non-core EPN symbiont. The association of P. protegens with nematodes appeared to berobust and the bacterium appeared to be well-adapted to the insect haemocoel, being able to rapidly proliferate after the injection of an even small amount of living cells (100 CFU) to larva, causing its fast death. The bacterium was also able to act by ingestion againstG. mellonella larvae (LC 50 = 4.0 × 10 7 CFU/ml), even if with a slower action. Specific bioassays showed varying levels of bacterial virulence on diverse target Diptera and LepidopteraP. protegens appears to have evolved its own potential as a stand-alone entomopathogen, however, the establishment of a stable association with entomoparasitic nematodes, would represent a special competitive advantage.