Scientists have found a way to protect Christmas veg from an unsightly plague of black spots
The Brussels sprout, that diminutive brassica that either makes or ruins your Christmas dinner, depending on your point of view, has been under the weather. And not just because of the recent cold snap.
Sprout plants have been suffering for some time from a plague of black spots caused by a viral infection. One large-scale farmer in Bedfordshire lost £75,000 five years ago, when his Christmas crop failed to reach the blemish-free standards demanded by the supermarkets and had to be fed to the sheep instead.
But researchers from Warwick University's school of life sciences have finally uncovered the genetic basis of a durable resistance to all strains of the virus, which has been known since the 19th century. The discovery could save the farming industry millions – not just in this country but worldwide. And not just in sprouts, but in all brassicas and, indeed, other crops. "A pox on your vegetables," is how Dr John Walsh describes the virus, dubbed the turnip mosaic virus (TuMV). "Yes, it affects turnips as well," he confirms.
In fact, this year's sprout crop is likely to be comparatively spot free, largely thanks to last winter's snow. "The aphid migration that spreads the virus was much reduced by the harsh conditions last January," says Walsh.
The life sciences school is based in the flat, crop-filled fields of south Warwickshire. When Walsh started here in 1983, it was still the National Vegetable Research Station, which had been set up in the post-war years to boost food production. Later it evolved into Horticulture Research International and finally became an outpost of the university. Backed by a £300,000 grant from the Biotechnology and Biological Sciences Research Council's crop research initiative, Warwick researchers have been sallying forth at regular intervals into the flat fields of Lincolnshire to collect samples to bring back to the lab for diagnostic tests.
"We were doing this for 14 years before we made the breakthrough," Walsh says. His team would find a resistant plant and spend a lot of time testing it against the pathogens (the agents that cause the disease). Then they'd find one or more of the strains of the virus would overcome the resistance. "The plant might be resistant to the one from the Czech Republic, but another from Canada might overcome the resistance, so we'd be back to the drawing board," says Walsh. "And so we went on. Getting to know your pathogen is crucial. It's like getting to know your enemy and playing on its weakness."
Eventually they found it. While working on a sample of Chinese cabbage, the researchers isolated the gene that controls resistance to the virus. They then had to test the plant against a range of different strains of the virus taken from all over the world. So far, no strain has been able to overcome the resistance. Next, the researchers carried out research to identify the plant genes responsible for the inherent virus resistance, with the result that the breeding process to develop plant varieties that are resistant to TuMV could be dramatically speeded up.
The team has applied for a patent and signed an agreement with the company Syngenta Seeds. "Their first target is Chinese cabbage because there's a massive market for this crop in Asia. They'll take our virus-resistant plant line and cross it with their commercial types." In the longer term, they can transfer the virus-resistant process to cabbage, cauliflower broccoli and sprouts.
Crunchy bits
Does the black spot affect the taste of sprouts or is it just another case of supermarkets pandering to those who eat with their eyes? "I think the dark bits would be a little crunchy, perhaps," says Walsh. "Growers call those spots cigar burns, particularly in cabbage. In sprouts, it's just the black spot."
The lead researcher confesses that he's partial to sprouts himself, and he's certainly earned the chance to enjoy them spot-free with his Christmas dinner. "This project has felt like a life's work," he says. "Some scientists can go through a whole career and never get anything to reach the market place."
Not that he plans to rest on his laurels, or indeed his Brussels. His team is now targeting another virus that has already infected 55% of one sprout crop in Lincolnshire this year. "The symptoms are more difficult to spot than TuMV because there are no marks," he says. "The crop is just stunted, and we have found this year it can reduce the yield of sprouts by 37%."
But thanks to researchers in Warwickshire, that diminutive brassica looks like remaining the traditional accompaniment to roast turkey for some years to come.