New oilseed rape ratings for yield-sapping disease

Oilseed rape growers can now check varieties for verticillium stem stripe resistance using a new rating system, which has been added to this year’s Recommended List (RL).

The new system sees oilseed rape varieties split into three categories: moderately resistant (MR), intermediate (I) and susceptible (S) to the disease, which has become more prevalent in recent years.

The update comes at a key time for oilseed rape growers as they decide which varieties to plant next season, following a difficult year for the crop as the UK area for rapeseed falls to its lowest for 40 years.

See also: Round-up of OSR varieties to drill in summer 2024

New rating

Paul Gosling, AHDB crop production systems senior scientist, says the disease rating follows 10 years of AHDB-funded research to develop a robust way of assessing the disease, which can otherwise cause up to one-third of lost yield.

“It quickly became evident that there were differences in varietal susceptibility, and a review of the RL identified the need for disease-resistance data.

“If you think your field is at risk from verticillium stem stripe, use the winter oilseed rape Recommended List to identify moderately resistant varieties and avoid the susceptible varieties,” explains Paul.

Varieties with moderate resistance include Murray, Tennyson and Adonis, while Ambassador was found to be a more susceptible variety.

The rating system steps away from the usual 1-9 scale, where 9 represents greater disease resistance. Instead, ratings are mapped in one of three disease-rating categories.

“These extreme categories are significantly different from each other at the 5% level,” notes Paul.

Verticillium stem stripe

Verticillium stem stripe (formerly called verticillium wilt) is a soil-borne fungus which, in severe cases, can lead to yield reductions of more than 30%.

Paul explains that with no fungicide treatment available, the only effective control is to widen rotations. However, this is often impractical as the gap between susceptible crops may need to be more than a decade.

The disease can survive in the soil for up to 10 years and builds when susceptible hosts, such as oilseed rape, are present.

Entering plants through their roots, from April onwards it causes leaves to turn yellow in the lower canopy. By the end of June and early July, brown vertical stripes appear on the stems.

Stripes extend along the whole plant during ripening and stems turn grey and shred. The roots of infected plants are also grey.

Severely diseased plants will ripen prematurely, with canopy collapse and seed shedding, which are exacerbated by high temperatures and drought stress.

Well-established crops with good root structure will reduce the chance of infection, which is active at a range of temperatures.

Growers are also advised to inspect crops for symptoms and not to save seed from diseased crops for resowing.

Crops in eastern England are often the most severely affected, although symptoms have been reported much more widely.

The AHDB is exhibiting at stand 526 at this year’s Cereals event, where growers can find out more about the Recommended List, pests, weeds and disease control and other industry advice.

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