Current research into combatting virus yellows includes the British Beet Research Organisation’s (BBRO) Operation Emerald Project, led by BBRO crop protection scientist Dr Alistair Wright, who is exploring how varieties respond to the different strains of virus yellows.
In last season’s trials, 100,000 plants were hand inoculated in the field to monitor their response to the different virus strains – beet mild yellowing virus (BMYV) beet yellowing virus (BYV) and beet chlorosis virus (BChV).
Speaking at BBRO’s Newark BeetTech event, Dr Wright said: “Breeders’ efforts are paying off and there were some very promising varieties coming forward.
There were strong differentiations in symptoms between the plots.
Some plots were infected with BMYV but held their yield.
That is unfortunately only for BMYV, but with BYV we still have a way to go.”
He also assessed sowing date effects for some of the emerging varieties, planting them in early and late March and mid-April to determine their response when hit with disease at different growth stages.
He said: “It was reassuring to see the more mature plants did not express symptoms and as part of that will hold out and stay greener, and therefore maintain yield.
Some varieties showed very static responses, regardless of the age of the plant.
But others showed a steep decline.
When BYV was assessed, we did not see the level of yield we saw in BMYV, which is not surprising given the virus is more severe, but some varieties did hold out better than others.”
Dr Wright said he is now able, using a drone, to quantify yellowing and what it means for yield loss.
“There is a very strong relationship between amount of yellowing and yield lost, no matter what strain of the virus it is.
This means hopefully in the next few years we’ll be able to predict how a variety performs long before it’s lifted.”
Delta variants PhD student Suzannah Cobb is exploring whether there are ‘Delta variants’ of BMYV and BChV to determine whether it is the same strains of the viruses infecting crops each year.
In 2021, 338 leaves were tested – of the leaves that tested positive for virus yellows, 75% were infected with BChV, 18% had BMYV and 7% had a mix of the two viruses.
Ms Cobb said: “I’m confident in saying BChV is more common in the UK crop than BMYV.
That is not the result we expected – we had thought it was BMYV that caused the most disease in the UK, but this data suggests that might not now be the case.”
When leaves were sent for sequencing to identify the strain of the virus, some mutations and differences were found in the isolates seen in the wild compared to the ones being reared at BBRO.
Ms Cobb said: “However, at the moment we don’t know if those mutations make a difference to yield or symptom severity.”
This season, BBRO will be performing a ‘world first’ field trial inoculating susceptible and BMYV-tolerant sugar beet varieties with wild isolates of BMYV and BChV which have been collected from fields in Norfolk, Suffolk, Lincolnshire and North Yorkshire