Screening the variability in oilseed rape resistance to pollen beetle attacks in the field and assessment of biochemical biomarkers

The pollen beetle (Brassicogethes aeneus) is one of the main insect pests affecting oilseed rape crops. Efficiency of insecticides used to control this pest is decreasing due to the development of resistance to compounds such as pyrethroids in many populations. Breeding oilseed rape for resistance to pollen beetle attacks could be an interesting strategy to find alternative control methods but has not been really developed in this crop yet. However, screening plants for insect resistance remains complicated as it often involves field tests on large genotype collections which are complicated to carry out without biases. Current knowledge on the chemical ecology of interactions between oilseed rape and pollen beetles could help finding biochemical markers of this resistance and bypass this problematic field screening phase, thus allowing an indirect breeding approach. Previous laboratory tests have shown that variations in attack levels among a small set of oilseed genotypes could be explained by the biochemistry of bud tissues. The present study aimed at validating this link under field conditions. For that purpose, we conducted a multi-site experiment in France with 19 genotypes exposed to pollen beetle attacks. We phenotyped pollen beetle damage and sampled buds in the field to assess their chemical composition. Large variability in pollen beetle attacks was observed over the genotypes. These attack levels were consistent between locations. Bud chemistry was highly variable, but most compounds were well correlated between locations. Potential biomarkers previously identified in laboratory experiments were not confirmed to be correlated with resistance to pollen beetles in the field, but new compounds which may be considered interesting markers for resistance screening against the pollen beetle emerged.