As featured in Arable Farming Magazine April 2021
First sclerotinia-tolerant WOSR hits the market
by Arable Farming
A breakthrough gene that can reduce sclerotinia outbreaks in oilseed rape crops by up to 75% has made it into the first commercial variety, without compromising yield or other disease resistance traits. Alice Dyer reports.
Hybrid variety PT303, from Corteva’s seed brand Pioneer, is the first winter oilseed rape variety with a claim for partial resistance to sclerotinia.
In Corteva trials with sclerotinia infection levels at 25% or above, the severity of the disease was reduced by 33% on average compared to non-tolerant varieties and by up to 75% in some cases.
Trials also showed that the higher the severity of disease, the greater the benefit from the trait.
But with no sclerotinia resistance rating in UK testing programmes, Pioneer Protector PT303 made it onto the AHDB Candidate List based on its other agronomic merits.
The variety delivered the highest gross output yields in each AHDB region, including a UK yield of 111%.
In the East/West it had a gross output yield of 116% and it also topped the North with a yield of 105%.
Corteva seeds and inoculants sales manager Andy Stainthorpe says: “This hybrid tops the Candidate List based on the existing protocol, without consideration for its sclerotinia tolerance.
Based on this, it ranks the highest candidate for gross output in all regions.
“It has a high oil content of 46.2%, 7 for stem canker, 6 for light leaf spot, as well as turnip yellows virus resistance.
It has high lodging resistance at 9 and an 8 for stem stiffness.
It is later to flower at 4 but its maturity is in line with control varieties on the list at 6.” PT303 will be considered for the AHDB Recommended List this autumn.
Breeding for resistance
Having identified a genetic source of sclerotinia tolerance, Corteva breeders have spent more than a decade crossing the source into regular hybrids through traditional breeding.
Jean-Claude Pruvot, head of Corteva oilseed rape research for Europe, who was part of the team developing the new trait, says: “With no known sclerotinia resistance in commercial varieties in Canada or Europe, our team has developed, through conventional breeding, sclerotinia tolerant material by collecting Asiatic sources.
With several cycles of recurrent selection, the team cumulated many genes contributing to disease tolerance with different modes of action.”
After several years of selection and stringent sclerotinia screening, the team identified inbreds with winter growth habits and strong disease tolerance, which would be used as the base germplasm for sclerotinia hybrid development.
Mr Pruvot says: “This material used in our hybrid breeding programme has demonstrated very good combining ability with high yield potential, showing the benefit of exotic blood.” Sclerotinia resistance is expressed in the leaf where it reduces disease entry points and in the stem where it helps to prevent spread of the disease throughout the plant.
Precise evaluation of the trait is made on disease incidence and severity – the two factors that are being reduced by genetic mechanisms.
As infection is highly dependent on weather conditions around flowering, hybrids are characterised for sclerotinia tolerance in multiple sites across Europe to be exposed to different weather patterns at flowering.
Mr Pruvot adds: “As the sclerotinia source has been [introduced] into our germplasm it exhibits the strengths of our conventional material – high oil, strong lodging tolerance and solid phoma and light leaf spot tolerance.
On top of this, it has turnip yellows virus tolerance, validated in French official trials.
“This is the kind of hybrid with broad commercialisation we are targeting in our strategy.”