Understanding interactions between biopesticides and partial crop resistance for management of aphid pests of brassica crops

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Aphids are important pests of crops and there is a need for new, environmentally sustainable methods for their control. In particular, there is potential for new integrated pest management systems based around biological control methods including resistant crop varieties, biopesticides and natural enemies. The aim of this project is to provide new knowledge on the interaction between partial host plant resistance in brassicas and fungal biopesticides for the control of cabbage aphid Brevicoryne brassicae, an important pest of brassica crops. Our IPM strategy is to use partial varietal resistance to slow down aphid developmental while at the same time enhancing the performance of biocontrol agents. Slower aphid development increases the time for which they are susceptible to entomopathogen infection (e.g. by preventing young instars 'escaping' from fungal spores by moulting). An added benefit is that partial resistance will be under a much lower selection pressure than major gene resistance and should prove more durable. Candidate Brassica accessions for partial resistance, identified through the scientific literature and by RNASeq analysis of a brassica diversity set for JA signalling pathway and camalexin production, will be screened in an infestation study using a B. brassica clone to determine aphid survival and rate of development. Validation for JA / camalexin will be done using rt-PCR. Laboratory bioassays will be used to quantify the effects of selected strains of entomopathogenic fungi (Beauveria, Metarhizium, Lecanicilliu, Isaria) on the survival and longevity of different life stages of B. brassicae feeding on Chinese cabbage B. rapa and a commercial variety of Brussels sprouts B. olereacea (as a baseline). Bioassays will then be done with a subset of fungal strains to determine their virulence to B. brassicae populations feeding on Brassica accessions that show partial aphid resistance. Comparisons will be made with susceptible plant accessions.