Monday, 18 February 2019
Once oilseed rape (OSR) has got up and away, many breathe a sigh of relief. But an emerged crop is not a problem-free guarantee. It continues to face attacks from pest and disease and the damage gets harder to quantify – no longer as black and white as ‘dead’ or ‘alive’, just nobbled to varying degrees.
With the withdrawal of neonicotinoid seed treatments and resistance to pyrethroids on the rise, cabbage stem flea beetle (CFSB) is one pest that has become increasingly difficult to control, especially when soil conditions hold back crop development.
Discovering why some fields or field patches succumb to CSFB while other parts escape unscathed is the subject of several AHDB research projects. In one PhD project, student Jessica Hughes has dedicated four years to study crop tolerance to the pest, looking at both the impact of adults and larvae.
Once CSFB eggs hatch, larvae burrow into leaf petioles and migrate to the main stem. Over the winter, they can cause significant damage to precious shoots. Jessica set out to look at the variation in OSR response to larvae, including differences in yield-preserving developmental responses, such as the crop growing around the larvae and the outgrowth of axillary buds.
The pest also infests other brassica crops. In fact, dramatic variation in pest damage has been observed among Sinapis alba and Brassica juncea varieties used in mustard production. As these varieties could hold valuable clues to the mechanisms behind pest tolerance, they too are being studied.
Jessica uses a set of OSR (Brassica napus) lines that represent the genetic diversity found in this species – called the Diversity Fixed Foundation Set (DFFS) – to study variation in pest damage. One avenue of investigation involves the use of ‘choice chambers’ (see picture, inset), which can be used to identify the plant lines that adult CSFB prefer to eat.
Jessica said: “The findings from the choice chamber experiments are clear-cut: beetles have a strong preference for some lines and a clear distaste for others.”
Experimental methods are also being developed in the studentship. For example, Jessica has found a reliable way to inoculate plants with CSFB eggs so that variability in larval damage can be assessed. Early results show significant variation in larval damage between B. napus/B. juncea and Sinapis alba. The intention is to identify the genes associated with the various degrees of palatability and crop tolerance and to design molecular markers to help breeders screen for resistance in variety trials.
Genetic basis of winter oilseed rape resistance to the cabbage stem flea beetle (21120064) runs from October 2017 until September 2021. The work is led by the John Innes Centre. Elsoms Seeds is an industry partner.