Safecross oilseed rape hybrids promise yield and trait improvements

Two new oilseed rape varieties created using a new hybrid production system are candidates in HGCA Recommended List trials this season.

Syngenta Seeds‘ NK Technic and NK Caravel have the highest seed yields of any candidates in RL trials, although a relatively low oil content means their gross output is 2-3% lower than the leading candidate variety, Dimension.

Future hybrids produced using the Safecross production system should overcome that limitation, says Gunther Stiewe, the firm’s European oilseed rape breeder, based in Bad Salzuflen, near Hanover, Germany.

“The first female used had lower oil content, but we’ve got second generations coming through.”

The firm sees hybrids as key to overcoming stresses such as extreme cold or lack of water, and helping to improve yields in emerging markets in eastern and southern Europe. “Hybrids are the only reasonable solution if you want crops to survive higher stresses,” Grzegorz Szreder, Syngenta Seeds’ oilseeds product manager, says.

In the UK, where those stresses are less important, the system could produce hybrids with better club root or phoma resistance, or to exploit the advantages of a semi-dwarf plant type. “We will have club root resistant varieties in two years,” Dr Stiewe notes.

Hybrid varieties are produced by crossing a “female” plant, which is male sterile (ie, does not produce pollen), with a fertile-pollen producing “male” plant, which restores 100% male fertility (ie, pollen-producing ability) in the seed collected at harvest from the female. That is the seed farmers will plant the following season.

In the widely used ogura hybrid production system, the male sterility was originally transferred in from radish plants. The drawback, breeders have found, is that other genes are also transferred at the same time, including ones that typically confer higher glucosinolate levels and poor phoma resistance, Dr Stiewe says.

A second complicating factor is that the male sterility genes were found within the radish cytoplasm DNA, which means not all pollen-producing fertile oilseed rape plants can fully restore the pollen-producing ability in the resulting seed from the female. “You need a restorer that can switch male sterility back on in the cytoplasm, and not all varieties can do that.”

With the Safecross system is it is easier to switch male fertility back on, says Dr Stiewe. “The male sterility comes from a single point mutation in the nuclear DNA. It means any pollen-producing oilseed rape plant restores the ability to pollinate.”

It gives breeders a lot more male restorer lines, or varieties, to choose from to cross with the sterile female, resulting in better hybrids. The specific nature of the male sterility mutation in the DNA should also stop those unwanted characteristics being transferred into the hybrid variety, he says.

Producing “females” is more tricky in the Safecross system, where sterility only lasts for one generation. Molecular marker analysis is used to quickly determine which plants are carrying the gene.

About 60 candidate female lines are being developed every year by Syngenta, before being whittled down to four after testing.

The other advantage Safecross brings is when new traits, such as better disease resistance or a modified oil profile, are identified, it should be easier to “drop” them into the core female line, says Nigel Padbury, UK technical manager for Syngenta Seeds.

“We should be able to bring in new traits faster than conventional back-crossing, and without the clutter that goes with the Ogura system.”

Tall hybrids favoured

Last year’s drought conditions in April favoured tall hybrid varieties, Mr Padbury notes. “If you look at this year’s candidates a large proportion of them are the higher biomass types. Time will tell if that is a weather pattern we see more of.

“But growers will need to be careful with their hybrid choices – Flash and Excel are also higher biomass hybrids – and particularly where they are placed.”