Isolation and identification of entomopathogenic nematode bacterial metabolites for biological control of fusarium head blight of wheat and wheat aphids

Abstract

Fungal diseases such as Fusarium head blight (FHB) and a complex of wheat aphids are significant biotic stressors, negatively affecting wheat production and quality. The use of chemicals and resistant cultivars is continuously challenged by the development of resistance, while harsh chemical pesticides pose environmental and human/animal health risks. This study explored the pesticidal activity of bacterial metabolites, produced by the bacterial symbionts of entomopathogenic nematodes (EPNs), against FHB causing Fusarium sp. Fusarium graminaerum and Russian wheat aphid biotypes. To achieve this aim, metabolites were isolated from the symbiotic bacteria derived from the EPNs collection at the Agricultural Research Council-Small Grain (ARC-SG). Metabolites were screened against Fusarium graminaerum and RWA biotypes, followed by the identification of nematodes, bacteria and metabolites. Mycelial growth and spore germination of F. graminaerum were differently inhibited by metabolites produced by bacterial symbionts of the nine selected EPNs isolates. Isolate SGI 197 and SGI 170 produce the highest overall mycelial growth inhibition rates of 96.25% and 95.79%, respectively. Out of the three types of metabolite treatments tested against mycelial growth, crude metabolites were the most effective compared to other metabolite treatments in all isolates. Xenorhabdus isolates displayed higher spore germination inhibition activity compared to Photorhabdus isolates. Among Xenorhabdus isolates, isolate SGI 257 had the highest spore germination inhibition rate of 96.29%, which was higher than that of other Xenorhabdus isolates. Crude metabolites were also screened for aphicidal activity on five RWA biotypes. The results depicted that resistance to metabolites increased with the order of the biotypes (from Biotype 1 to 5). Isolate SGI 197 had the highest overall aphicidal activity when compared to other isolates and the control. LC-MS analysis and molecular networking computational tools detected and confirmed the presence of two previously described antimicrobial compounds, Anthraquinones (m/z 255/285) and stilbene precursor 3,5-dihydroxy-4-isopropyl-trans-stilbene (Isopropylstilbene) (m/z 255); and a number of other unidentified compounds. The results from this study are based on in vitro assays. More studies are needed to evaluate the antifungal and insecticidal activities of these bacterial metabolites on in vivo conditions. Among the selected isolates, Isolate SGI 197 seemed to be the best candidate for use as a biopesticide. These are baseline steps towards the development of cheaper and more eco-friendly pest control products based on the metabolites.