Date: 04/2023

New genetic resistances to two of the UK's most serious and costly diseases affecting oilseed rape, should be available to growers in the next few years, say breeders DSV.

The company's Phoma Blocker trait, featuring a resistance mechanism for phoma stem canker completely new to Europe, is already featured in varieties currently going through the UK testing process with the enhanced clubroot resistance CRE1 following closely behind.

According to Simon Kröger, DSV oil crops product management lead, phoma stem canker in oilseed rape is a disease now costing UK producers £100M/year through lost yield and the costs involved in trying to control it.

"Resistance to phoma results in better and longer lasting plant health with better lodging resistance as well as a longer and undisturbed assimilation process that supports growth through tough climate conditions such as early summer drought."

"It also underpins optimum harvest date and can lead to higher yields as well as reducing the general level of phoma spores in the field."

But while RLM7 has been the main genetic disease resistance mechanism for many years there is growing evidence that its effectiveness is reducing, he explains.

"In DSV trials in Dyngby in Denmark, for example, on a scale of 0 - 10 with 0 being excellent resistance and 10 being high susceptibility to Phoma, varieties without any qualitative resistance showed an average score of 7.5 with a range of 6.5 to 8.5."

"Varieties with the RLM7 gene showed a wider range of phoma susceptibility scores - from 4 to 9 -  but of real concern is that the average was the same 7.5 as varieties with no disease resistance at all."

"When you consider 53% of oilseed rape varieties on the current 2023/24 AHDB Recommended List for the UK rely on RLM7 as the mainstay of their protection against this yield-robbing disease, clearly this is a very worrying situation."


Additional layer of security

RLMS provides some hope DSV Phoma Blocker adds a much-required additional layer of security for the future, he believes.

"At the heart of Phoma Blocker is LepR1 - a completely new type of genetic mechanism for phoma resistance in Europe."

"Whilst LepR1 by itself has been shown to have the best resistance to the most common phoma strains in field trials across Europe, we believe it is most effective when used in conjunction with other disease resistance traits."

"DSV Phoma Blocker is made up of LepR1 with RLM7 and this combination achieved an average of score of just 2.3 in the Dyngby trials - compared to the 7.5 for RLM7 by itself."

But the real advantage is that DSV now uniquely has varieties featuring all three different phoma resistance mechanisms - RLM7, RLMS and now LepR1 - that can be rotated in the field to minimise major breakdown of any one type of resistance, Simon Kröger points out.

"By being able to do this, DSV has taken phoma resistance in oilseed rape several stages further on."

"DSV already has Phoma Blocker varieties moving through the UK testing process and it fully anticipates the first of these will be commercially available in 2024 after completing NL2 testing this year."

According to DSV UK managing director Dr. Alex Doering, new genetics to improve resistance against the growing threat of clubroot are also being introduced by the company.

"Clubroot, caused by the pathogen Plasmodiophora brassicae (P. brassicae), is a highly infectious, yield-robbing disease of growing concern across Europe."

"In the UK, Scotland has experienced heavy infestation in recent years, but there is growing evidence that the problem now exists in many other regions including the South East of England."

Strategies to control clubroot involve a combination of different approaches. For a start early destruction of OSR volunteers and cruciferous weeds either chemically or mechanically is essential after the previous crop is harvested, he says.

"Cruciferous weeds must be combated as quickly and precisely as possible as weed infestation in one field is often the reason why clubroot still occurs after very long breaks in cultivation."

"Volunteer rape is also a latent danger with early control of OSR volunteers shown to reduce intensity of clubroot and further multiplication of spores. Growing OSR no more than one year in five on the same field is also important.


Enhanced clubroot protection

In recent years, hybrid oilseed rapes with genetic clubroot protection have also played an important role in keeping spread of the disease in check and also protecting yields for growers, he points out.

"DSV has been particularly successful in this area with varieties such as DSV Crossfit CR and DSV Crocodile CR offering good protection without yields being compromised, which has usually been the case before such varieties were introduced."

"Breeding for clubroot resistance is complicated and time consuming with significant incompatibilities between species creating an additional challenge for breeders."

Despite this, DSV is now introducing a new clubroot resistance mechanism called CRE1 (Clubroot Resistance Enhanced 1) with a broader protection against more pathotypes, Alex Doering says.

"CRE1 is a novel trait that has been created by crossing from B. rapa. Laboratory infection studies using various P. brassicae isolates show CRE1 to be an enhanced resistance mechanism compared to the classical  resistance."

"The first DSV CRE1 resistant variety is expected to be registered during winter 2023/24 in the EU, but it will take a few more years until it is available in the UK."

"In the meantime, we are launching a new variety (RAP637) which as well has a clubroot protection using the established common source of partial resistance, will also be TuYV resistant with Verticillium wilt tolerance and a very good lodging resistance score."