Oilseed rape


Resistant rape varieties help fight


clubroot threat • Choose varieties to obtain best results • Test soils for spores and acidity • Longer rotations can help reduce risk


T


ighter rotations and wet- ter seasons are increas- ing the threat of clubroot


in England, says an oilseed rape breeder. Clubroot can cause yield losses of 50% of potential – or even crop loss with severe infections. While the problem is perceived to be an issue for Scotland and the Borders, in reality clubroot has now become an issue in the wetter parts of the rest of Eng- land as well,” warns Theo Labu- da, managing director of LS Plant Breeding (LSPB). Growers


in at-risk areas


should investigate patches of poor growth and regard it as routine to get soils tested for clubroot and pH, says Mr Labuda. Warning signs are wilted or stunted plants in hot, dry weather, he adds.


Spores released


Large galls on roots formed by the clubroot pathogen, Plasmo- diophora brassicae, affect nor- mal root function, reducing wa- ter and nutrient uptake. As the gall decays, spores are then re- leased back into the soil where they can persist for 15-20 years. As general good practice, well- spaced rotations of oilseed rape, cereals and pulses should be standard practice - with oilseed


rape one year in five or more as optimal. Varietal choice should also be an important part of growers’ clu- broot armoury, with Mentor as the only variety on the 2017/8 AHDB Recommended List of winter oilseed rape for both the east/west and north regions with a ‘specific recommendation’. Mentor is resistant to common strains of clubroot and is a medi- um-early maturing variety with good seed yield combined with high oil content to give high gross output. Agronomic characters are that it has good stem stiffness and


resistance to lodging and is of me- dium height.


Further progress Mentor may, however, be infect- ed by some strains and infections that have been reported in some fields, so over-reliance in close ro- tations should be avoided. There is now further pro- gress on the varietal front with LSPB’s Crome currently pro- gressing through official trials as a UK Recommended List candi- date this year, to be commercially available for 2019 drilling. Crome has a higher seed yield


Mentor is resistant to common strains of clubroot


than Mentor, and its increased oil content of 46.7% brings a very worthwhile 3.7% higher gross output based on trials to date. Agronomic characters are also better with boost to LLS resist- ance rating from 5.7 to 6.3. “A number of varieties have passed through trials over recent years but fallen by the wayside,” says Mr Labuda. “We are giving growers a worthwhile addition to their ar- moury against yield-sapping clu- broot to add to the equally im- portant strategy of well-spaced rotations of oilseed rape.”


More must be done to manage risk


Clubroot is an increasing challenge for oilseed rape crops and more must be done to manage the risks, says Limagrain’s Vasilis Gegas. Losses exceed 50% of yield potential in


the worst-affected crops, Dr Gegas explains. “We’re seeing more cases around the country, and for growers in hotspot areas there’s a high proportion who have at least one field affected.” Clubroot incidence is rising possibly as


climate change results in more frequent, milder and wetter winters. “It is why the disease is our most heavily-invested oilseed rape breeding trait, aside from turnip yellows virus.” Resistant hybrid varieties, such as


Archimedes, offer a valuable option for growing rape on infected land. But newcomer Alasco promises to virtually eliminate the “yield drag” associated with resistant varieties in the past. “Alasco is the next generation of clubroot


resistant varieties, with a yield close to mainstream varieties and oil content 3% higher than Archimedes,” says Dr Gegas. Alasco retains and enhances many of the


traits in Archimedes that were developed specifically for northern areas. These include robust light leaf spot resistance, short stiff straw, pod shatter resistance and early maturity.


But while genetic resistance is very effective,


Wetter soils can increase the threat of clubroot in OSR


the clubroot pathogen (Plasmodiophora brassicae) is capable of evolving and


New varieties cut ‘yield drag’ – Vasilis Gegas


overcoming resistance, so genetics must be supported with good husbandry and stewardship. Dr Gegas advises against growing resistant


varieties unless clubroot is a significant problem. Extended rotations of at least one year in seven or eight, and careful soil management must also be used to control disease, he says.


JULY 2018 • ANGLIA FARMER 29


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