Why low biomass hybrids can cut the risk of OSR growing

The latest semi-dwarf winter oilseed rape to join the Recommended List is the first in a new generation of low biomass hybrids that promises to solve some of the current challenges of growing the crop.

Oilseed rape growing has in recent years been a more risky affair, with the challenges of high input costs, spray timing difficulties and harvest management putting pressure on profits.

But this may be about to change with the first of a new generation of low biomass hybrids from a dedicated Dekalb pipeline, offering high yields and less risk of significant disease pressure. 

See also: Latest turnip yellows resistant OSR shows increased yield

Secret, which is on both the East/West region and the North region lists, shows a 6% improvement in gross output performance over existing semi-dwarf varieties, as well as better disease resistance ratings and earlier maturity.

As such, Alexandra Cadet, European technical development specialist at Dekalb, believes the new variety could be a solution.

Semi-dwarf trait

“Combining yield performance with a low biomass profile was the company’s aim when it laid the foundations of this particular breeding pipeline 10 years ago and inserted the semi-dwarfism trait,” she says.

“We see low biomass hybrids such as Secret as an opportunity to manage risk and introduce some flexibility into oilseed rape growing.”

Including the Dekalb traits of pod shatter and double phoma resistance in the breeding programme means that these varieties will also be suited to different growing conditions, as confirmed by Secret’s UK-wide recommendation, she notes.

“We have the same high expectations of the new generation as we do of our standard hybrids. They are developed and tested in exactly the same way across Europe.”

Secret’s very short, stiff plants are 30-40cm below the height of standard-sized hybrid varieties, so offer potential advantages with fungicide use and harvest management.

Easier management and harvest

“The variety has a shorter flowering period, due to its plant architecture,” explains Mrs Cadet. “Less apical dominance means that the side branches flower at the same time as the main stem, making sclerotinia management easier.”

At harvest, putting less biomass through the combine results in a 30-40% increase in the area cut per hour, with associated time and fuel savings.

Dick Neale, technical manager at Hutchinsons, believes their harvest efficiency is an undervalued feature.

“We’ve measured a 40% increase in harvesting output, which can be as much as 7.5ha/hour,” he says.

Mrs Cadet adds that the shorter size has no impact on the number of seeds produced per sq m, which is why yields are competitive.

Low biomass hybrids also develop strong, early rooting systems, which helps with the early uptake of water and nutrients, she explains.

“They have a different rooting dynamic, which we are still learning about,” says Mrs Cadet. “This has potential for these types to be used in drought management strategies, especially in eastern Europe.”

Mr Neale is confident that the new semi-dwarf varieties are “in the mix” for yield.

“The RL system probably doesn’t do them any favours, but statistically they’re the same for gross output in our trials.” he adds.

Secret: at a glance

Gross output  100% (East/West) and 97% (North)
Oil content  44.5%
Phoma  8
Light leaf spot  7
Lodging    8
Stem stiffness 8
Maturity   6
Flowering  7
Height 9

Low biomass OSR crops in practice

Semi-dwarf varieties are fundamentally different to conventional varieties with a natural shortness in the stem, although both can be referred to as low biomass, explains Hutchinsons technical manager Dick Neale.

“The semi-dwarf trait is of interest for management reasons, but getting the best from it means understanding the very different growth habit that results from its inclusion,” he says.

While the agronomy of a standard variety and a semi-dwarf type is the same, the semi-dwarf types don’t have stem growth and go into canopy expansion from the ground level, he adds.

“This means they don’t grow away vigorously in the autumn, but produce leaf and a good root system instead.”

Higher seed rates

As a result, they tend to have a smaller plant in the winter, so higher seed rates of up to 80 seeds/sq m are beneficial, he believes.

“Having a thick crop with good ground cover in the winter helps to overcome the various pest and weed challenges. The leaf cover tends to black the soil out, preventing the germination of weeds.”

In the spring, flower buds appear just above the mass of tight leaf production, with flowers forming on the main raceme and branches at the same time.

“Once it’s flowering, you can forget it’s a semi-dwarf – the only thing that’s missing is 18in of stem.”

Growth regulation

That means nitrogen and plant growth regulator use is the same as a standard variety, as is the need to control insect pests, Mr Neale advises.

“Nothing is hidden with semi-dwarves, because any spray misses are very apparent, sticking out of the top of the crop. That may have given the perception that they are not competitive, which is wrong.”

Finally, he says they are suited to most sites, except for those with very thin soils and low fertility.