Early results from a nationwide survey are indicatinghigh incidences of TuYV infection in the current oilseed rape crop.
Carried out by Dr John Walsh of Warwick University onbehalf of breeders Limagrain UK, the survey which will be completed by the end of May, willprovide a comprehensive indication of TuYV infection hotspots across thecountry. TuYV is thought tobe the most important, yet least understood viral disease in oilseed rape.
Results so farare showing generally high levels of infection; results from the south ofEngland have detected incidences of as high as 80%, in Somerset incidences ofup to 74% and in Yorkshire incidences of up to 72%, whereas in Cardiganshire wefound incidences of up to 46%.
Dr Walshbelieves that these high incidences have come about as a result of the highnumbers of aphids flying lastautumn and to some extent the lack of neonicotinoid seed treatments.
What we do knowis that high incidences of TuYV infection lead to fairly substantial yieldlosses and with levels such as those indicated in the survey so far, we couldbe looking at yield losses of as much as 30%, says Dr Vasilis Gegas, senioroilseed rape breeder with Limagrain.
William Compson,oilseeds product manager with Limagrain, recognizes that the problem with TuYVis that you dont usually see the symptoms until spring. Early symptoms ofTuYV are expressed by intense purpling of the leaves; later symptoms ofinterveinal yellowing and reddening of leaf margins are not usually expressedbefore stem extension and can easily be confused with other stress symptoms andnutritional deficiencies, which is why the effect of the virus isunderestimated.
Looking ahead tonext autumn and what this means for the oilseed rape crop, Mr Compson notesthat whilst foliar insecticides such as Plenum, can offer some solution to theaphid problem, there is widespread resistance to pyrethroids and primicarb toconsider.
This means thatvariety choice will be even more critical than ever and will require a changein mind set where resistance and agronomics play an increasingly crucial rolein order to protect yield, he says.
Amalie remainsthe only commercially oilseed rape variety with resistance to TuYV on themarket, and the variety was re-submitted as a candidate in the 2014-2015 HGCARL trials based on this trait.
We are seeingthe benefits of this resistance in field trials during our sampling, adds DrWalsh. One of the farms in Lincolnshire where we conducted our sampling showedincidences were between 36-62%, depending on which field was sampled. However,this particular farmer had some Amalie growing adjacent to these non-Amaliefields and the incidence in the Amalie crop was only 7% – a drastic reduction.
Amalie is aconventional OSR variety that offers a gross output similar to the widely grownvariety, DK Cabernet. However, our own trials using untreated seed over thelast four years have clearly shown that where TuYV is present, Amalie yields10% more than non-resistant varieties, says Mr Compson.