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Making short work of oilseed rape The visibly shorter DK Secret on the right, alongside DK Exception.

Thanks to a new generation of low biomass oilseed rape varieties, the yield gap between so-called semi-dwarf types and the top yielders on the Recommended List is closing. Despite their different growth habit in the spring, and shorter height, the advice for growers wishing to try semi-dwarf types on farm is to treat them as they would any other OSR variety. Dominic Kilburn writes. It’s been a decade since oilseed rape breeder Dekalb first registered a low biomass ‘semi-dwarf’ hybrid in the UK in the shape of DK Secure; a variety that the company describes as the foundation of its low biomass pipeline. Since then Dekalb has worked hard, it says, at trying to balance the agronomic benefits delivered by growing low biomass varieties against the yield drag effect of the semi-dwarf gene found in true low biomass types – with the ultimate aim of competing with the yields of the Recommended List’s top performing conventional hybrids and conventionally-bred (open pollinated) material. However a new generation of low biomass varieties from the company, kicking off with fully recommended DK Secret, is now in touching distance yield-wise of top yielding varieties on the List.

The yield gap has closed and there is more low biomass pipeline material to come, highlights the company. Speaking at a recent event hosted jointly by the breeder and crop protection business Hutchinsons, Dekalb’s European technical development specialist Alexandra Cadet, said that there had been a huge investment in developing the company’s low biomass hybrid pipeline, initially testing in small plot replicated trials across Europe to assess local performance, plant behaviour and characteristics. “We use the same tools for breeding low biomass hybrids as we do for our standard hybrid pipeline and so we have the same level of expectation in terms of a full combination of yield preserving traits in addition to the low biomass profile,” she pointed out. Pan-European large strip

Dekalb’s European technical development specialist Alexandra Cadet compares the height difference between DK Secret (left) and DK Exception.

trials and Dekalb ‘Technology Centres’ (of which there are two in the UK) are then used to finetune the positioning, growing recommendations and benefits of the varieties for farmers in extremely different growing environments, she explained. “As a result we are convinced that our new generation of low biomass hybrids can be an opportunity to manage risk, offer flexibility and fit different growing conditions.” She went on to list some of the key benefits of growing the new generation of low biomass varieties (see summary box), including recent work by ADAS which demonstrated that the low biomass characteristic of a Dekalb hybrid was limited to its foliar development and not translated to the rooting system. “The trials have shown that at the early stage of development, these low biomass hybrids have the highest roots and shoot biomass – significantly higher than OP varieties. “Practically, that is translated into an ability to develop strong, early rooting and then have a great ability for early uptake of water and nutrients,” she added.

Low biomass difference Also speaking at the event was Hutchinsons’ technical manager, Dick Neale, who has been studying low biomass varieties, and advocating their management benefits, since 2009. He began by explaining that there was a difference between varieties that were given a low biomass tag. “There’s low biomass, and then there’s low biomass,” he stressed. “There are conventional hybrids that are bred to be shorter than the typical oilseed rape plant height, and there are those which carry a semi-dwarf gene, and these are much shorter.” Mr Neale said that it was important for growers to understand the growth habit of true low biomass varieties when considering their use on farm as they all look and behave in the same way in early spring. “The agronomy requirement of all oilseed rape is the same – but the way low biomass varieties express their growth is different. “Conventional varieties grow away in the spring but low biomass don’t. They sit there with a lot of leaf and cover the ground, blocking out light to the soil and providing very good competition for weeds.

Hutchinsons’ technical manager, Dick Neale.

Trials have shown that they have a similar green area index (GAI) to conventional varieties. “Effectively, all OSR is at the same growth stage throughout the season but low biomass semi-dwarf varieties are not wasting time by growing 18in of stem like others, which doesn’t provide any extra value. It’s the root to pod connection which is the key aspect for yield later in the season. “The height difference between them and conventional varieties remains the same all season but they have canopy expansion and branching from the ground level,” he added. Mr Neale said that an important factor with semi-dwarf varieties is that they offer flexibility to increase seed rates with very little risk. He pointed out that there’s a very good argument for higher seed rates in oilseed rape crops to provide more plants to overcome the threat from pests such as flea beetle, pigeon and slugs, as well as competing with SU resistant weeds that come through with the crop. “Even if you don’t get those problems, because of their short height and stem stiffness, low biomass crops won’t then fall over and cause a disaster,” he explained. He suggested that while a conventional hybrid seed rate recommendation was typically around 50 seeds/m2, anything up to 80 seeds/m2 would be suitable for a low biomass variety where there is a likelihood of pest and weed pressure.

Flowering According to Mr Neale, just like other hybrids and OP varieties, semi-dwarf types vary in flowering time and growers can select them for early or later flowering. “You can forget it’s a semi-dwarf variety at flowering continued over...

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