Biopesticide treatments with novel mode of action and optimized for an improved activity toward their biological targets (fungi, insects, weeds, mycotoxin biosynthesis) after test

Naturally occurring substances produced by plants or other organisms offer alternatives to synthetic pesticides to control pests, diseases and weeds and new leads when resistance has evolved to currently available pesticides. In vitro bioassays were conducted to evaluate the efficacy of different molecules in combatting target pests.

Whole extracts and fractions of the ground pine, Ajuga chamaepitys, which may contain potential antifeedant clerodane diterpenoids, were tested for their biological activity on the diamondback Plutella xylostella and tomato leaf miner Tuta absoluta. Other secondary metabolites, phenolic acids and benzoxazinoids, were tested for their biological activity against several insect species, and for inhibition of mycotoxin production by Fusarium sp. in wheat. With the aim of restoring sensitivity to herbicides, key genes involved in herbicide detoxication in wild grass were characterized and transgenic (rice) lines overexpressing detoxifying enzymes were generated. This allowed screening for inhibitors of detoxifying enzymes, including protein kinases.

Knowledge was acquired on the spectrum of action of these biomolecules in order to define the scope in terms of insect pests to be targeted. Whole extracts of A. chamaepitys reduced feeding damage by larvae of the two Lepidoptera insect species studied. Dicaffeoylquinic acids showed no effect on insects of the Coleoptera and Lepidoptera orders, but were highly toxic to a wide range of aphid species.

The mode of action of the active compounds was investigated. Although significantly different from the control, none of the fractions of A. chamaepitys extract were as good as the whole extract for antifeedant activity, and the active components remain to be identified. After topical application of dicaffeoylquinic acids, aphid mortality was low, but still varied with the experiments, suggesting that the contact efficacy can be improved with an optimized formulation of dicaffeoyl-based biopesticides. Monitoring of the aphid feeding behavior showed that ingestion of 3,5-dicaffeoylquinic acid-supplemented diet was severely impaired, but that aphids could not detect the presence of the molecule before ingestion. The mechanisms by which phenolic acids may limit the accumulation of mycotoxins in kernels have been studied. Phenolics are able to modulate the expression of the biosynthesis genes, and their effect may also be linked to their antioxidative properties.

 

Field trials have been conducted to evaluate the efficiency of phenolic acid spray applications to protect wheat plants from Fusarium graminearum. Like with aphids, the results obtained with mycotoxins suggest that experiments need to be repeated after an optimized formulation is found for use of these compounds as crop protection agents. Another method to increase protection against Fusarium sp. would be breeding or engineering of plants with increased levels of benzoxazinoids

The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/ 2007-2013) under the grant agreement n°265865- PURE