Ten years in the making, ST Tweed poses one of the first in a generation of new virus yellows-tolerant sugar beet varieties. Now entering its second season of availability, CPM speaks to breeder Strube, to find out why it should pique grower interest.
“Maintaining yield and overall resilience is essential, which is what we were striving for with ST Tweed.” RICHARD COGMAN
By Janine Adamson
According to Strube’s Richard Cogman, ST Tweed is a prime example of what can be achieved following a 10-year, targeted sugar beet breeding programme. The variety – one of the first to deliver virus yellows tolerance – offers a robust package, he adds, and is expected to be reliable and stable in its ‘real world’ performance.
While Tweed became commercially available earlier this year, its story began long before, explains Richard. “Anticipating that the beet industry’s reliance on neonicotinoid seed treatments was under threat, Strube commenced breeding and field trials for virus yellows tolerance in 2015.
“In ways this was timely, given the very high incidence of virus yellows in 2020 where the value of the loss was estimated at more than £65M – equivalent to around 25% yield loss.”
EMERGENCY AUTHORISATION
This high pressure year did lead to an emergency authorisation for neonicotinoid seed treatments between 2022 and 2024, which had previously been banned in 2019. However, moving forward without this option leaves two main solutions, points out Richard.
“Although growers can use foliar insecticides to combat the aphid vectors of beet viruses, the insect’s ability to adapt and develop almost complete resistance remains strong. This was a key reason why the industry turned to insecticidal seed treatments in the first place.
“So while these are currently applied in accordance to monitoring and thresholds, their long-term future is under question. This means varietal tolerance is critical in the fight against viruses in beet,” he stresses.
Delving into in more detail, Richard highlights that the earliest understanding of ‘beet yellows virus’ (BYV) dates back around 90 years, but it wasn’t until the early 1950s that the aphid species responsible for transmission were identified.
At the same time, another less yield impactful virus was detected, now known as ‘beet mild yellows virus’ (BMYV). Then in the 1980s and 90s, a new virus was discovered, later named ‘beet chlorosis virus’ (BChV) – forming the three-virus complex faced by growers today.
Results from BBRO’s 2024 Goliath trial suggest Tweed is highly tolerant to poleroviruses (BChV and BMYV) when compared with controls, raises Richard. “It’s well documented that poleroviruses can reduce yield by 24-27%. This risk is increased by their greater prevalence in recent years when compared with closterovirus BYV, which is generally more fluctuating.
“Tweed is promising because in the trials it retained around 88% and 95% of its yield against 100% inoculation of BChV and BMYV, respectively. This demonstrates the variety’s tolerance to both viruses; we knew it had potential, but the trial has provided hard, independent evidence.
“Furthermore, accompanied by aphicides applied at threshold before the crop reaches ‘mature plant resistance’ at 12-14 leaf growth stage, Tweed can offer a high level of protection against these devastating viruses.”
As for the specific genetics involved in achieving this tolerance, Richard says they’re derived entirely from Strube’s own ‘pool’ and internal classic breeding programme. He also points out that they’re based on a multi-gene tolerance mechanism, rather than single gene, to help future-proof.
But critically, has this genetic advancement come at a cost? Richard believes not. “Tweed is very low bolting and has excellent canopy health; it scores an 8 for cercospora (2026 RL) and is also better than average for rust and powdery mildew.
“Breeders must stack traits for cumulative benefits that align with the demands and challenges UK beet growers face. Maintaining yield and overall resilience is essential, which is what we were striving for with Tweed.”
FROM THE FIELD
Suffolk arable farmer, James Faulds, opted to grow Tweed this season for its virus tolerance. On heavy land, the farm’s sugar beet crop is both drilled and lifted early, with risk management a key priority.
“Although we’re not as exposed to virus yellows as other growers, I’ve seen the damage it can do so it’s something I’m very cautious of. That’s why I decided to add more diversity into our beet by growing Tweed.”
Having just harvested the crop he says it’s showing promise. “We drilled into good seedbed conditions at 15cm row spacing, although the weather meant the ground did dry up quickly.
“Even so, we achieved a stand of around 110,000 plants/ha with a decent canopy structure. Now at harvest, the crop’s root size is surprisingly large despite the lack of moisture. Trial digs 10 days ago suggested 87t/ha at 18% sugar, so if we achieve that, I’ll be happy.”
James says based on these numbers, Tweed has delivered a solid performance that’s on par with the other varieties he’d usually grow. “I don’t see any negatives so far, it’s a good all-rounder.
“The only other trait we require is low bolting due to our early drilling window. We had a few bolters in the crop of Tweed, but nothing consequential,” he adds.
For those growers without a virus yellows problem, the relevance of Tweed may be questioned; Richard proposes there are two other Strube varieties which could appeal.
“Ultimately, varieties have to align with what growers are facing on their land, while respecting the requirements of British Sugar and BBRO. For those looking for an all-round yield builder, there’s Morgan, which has a treated adjusted yield of 96.8 and demonstrates good all round resilience.
“While if the main challenge is beet cyst nematode (BCN), Button is a tolerant variety aimed specifically at that market,” he explains.
For now, these three varieties are being marketed by Strube, but following the company’s recent acquisition by RAGT, there’s a transition to become one combined force.
Richard believes the move will enable greater investment and resource into the sugar beet breeding work Strube has conducted so far. “Growers can expect to see further progress to support yield stability from pest and disease pressure through resilient genetics and the combination of multi-tolerance traits.
“This will be the direction of our candidate pipeline into trialling for national (now VL) listing, then RL listing and commercial reality; breeding progress together,” he concludes.
This article was taken from the latest issue of CPM. Read the article in full here.
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