14 July 1995

Composite hybrids are under extra scrutiny

COMPOSITE oilseed rape hybrids have worked well in France, but clearly need special treatment, delegates at the International Rapeseed Congress heard last week. And if concerns about poor pod set in eastern France are borne out, production may need limiting to specific areas.

The approach, which achieves the high yield benefits of a hybrid by growing a low rate of pollinator plants and a higher rate of male sterile plants in the same field, is due for commercialisation in the UK this autumn by CPB Twyford, using French variety Synergy.

Official trials on the crop last year included 46 variety trials in fields and 10 special isolated by oilseeds organisation, CETIOM.

Yield was 6% ahead of the latest conventional variety Goeland, said Xavier Pinochet of CETIOM in Dijon, France. Oil and glucosinolate contents were no problem, and although the crop was higher than many conventional lines, lodging did not appear to be a significant risk. The crop also seems better able to scavenge nitrogen from soils, said Mr Pinochet.

He concluded that no major change to management was needed, apart from the need for a low plant density, due to the poor competitive ability of the pollinator line. Populations of 20-40 plants a square metre may be adequate, he suggested.

Doubts about stress

But while he stressed the crops ability to compensate, he added the proviso that results were from one year only.

Indeed, doubts are being cast on the crops ability to withstand stress at flowering time. Poor pod set in eastern France has left the lower branches of some crops bare this year. The cause could be cold weather either side of flowering and hot weather with cold nights during flowering, or problems with competition for nutrients and light, said Mr Pinochet.

French researcher Jacques Morice, who helped develop the composite hybrid, agreed pod set was poor in some parts of France. He blamed "extreme conditions". If there is a yield problem he suggested the crop may need restricting to the less variable areas of the country. But he refuted the suggestion that composite hybrids could earn true hybrids a bad name before they come on to the market. Indeed, he suggested that the male sterile lines could still be mixed with full hybrids, since they are inherently 5-10% higher yielding, as they waste no energy on pollen production.

Mr Pinochets trials confirm that, showing more pods and higher yields from the male sterile component of a composite hybrid, provided it has a pollen supply.