Larval antibiosis to cabbage stem flea beetle (Psylliodes chrysocephala) is absent within oilseed rape (Brassica napus)

BACKGROUNDInsect pests present a global threat to crops, with plant resistance representing a key breeding goal. The cabbage stem flea beetle (Psylliodes chrysocephala; CSFB) is the most damaging pest of oilseed rape (Brassica napus; OSR) within Europe; however, CSFB resistance is yet to be found within B. napus. To address this, we examine CSFB larval development over time, explore antibiosis across a diverse Brassica panel, and test whether larvae can develop within model Brassica relatives (Brassica rapa and Arabidopsis thaliana). RESULTSCSFB larvae completed development from four weeks post-infestation, undergoing a 20-fold size increase, with larval recovery after two weeks allowing semi-high throughput resistance phenotyping. Applying this method to 98 Brassica genotypes (97 B. napus and a single Sinapis alba), we found weak evidence for genotype effects on larval survival, however phenotype validation with resistant and susceptible B. napus genotypes showed no differences in larval survival or adult emergence. Larval antibiosis was consistently observed in S. alba. Finally, we showed that B. rapa and A. thaliana represent suitable hosts for CSFB, with larvae increasing 8-10x in size after two weeks. CONCLUSIONCSFB larval antibiosis appears absent within B. napus, possibly due to bottlenecks experienced during domestication. However, larval antibiosis is present within S. alba, and future work should study the basis of this resistance. Further, CSFB larval screening in Brassica relatives presents an opportunity to explore CSFB resistance genetics, informing breeding progress for insect resistance in B. napus.