Acción nematicida de Photorhabdus laumondi laumond iLP1900 sobre el nematodo de vida libre Panagrellus redivivus

Abstract

Photorhabdus spp. (Enterobacteriaceae) lives symbiotically within Heterorhabditis nematodes. It is known that secondary metabolites of this gram-negative bacterium exhibits insecticidal activity, mainly in Lepidoptera and Coleoptera insects. Recent studies have also shown that cell-free culture filtrates of Photorhabdus spp. have nematicidal activity on free-living nematodes and phytonematodes. The objective of this work was to evaluate the nematicidal activity of the native strain for Argentina Photorhabdus laumondi laumondi LP1900 on the free-living nematode Panagrellus redivivus. Two types of assays were carried out: i) LP1900 strain was massively grown on nutrient agar plates (5 replicates) for 1-21 days at 29°C, then 2x103 nematodes were inoculated on each plate and the mortality recorded after 24 h; ii) LP1900 strain was grown on nutrient broth for 72 h at 250 rpm. Three hundred microliters of different culture preparations (whole culture/resuspended cell pellet/filtered supernatants) were poured into each well of a 24-well plate. Eighteen juveniles of P. redivivus were used for each assay (2 replicates). Mortality was registered after 24 h at 29ºC. Sterile distilled water or nutrient broth was added to the natural mortality controls. Panagrellus redivivus mortality was higher as the age of the tested culture in nutrient agar was older. The highest mortality values were obtained in 7 and 14-days plates (81-82% respectively). On the other hand, all liquid culture fractions tested showed high levels of nematicidal activity (61-100% mortality). In conclusion, LP1900 strain caused age of the culture-dependent mortality in P. redivivus and, unexpectedly, resuspended cell pellet fraction was highly active.