FRENCH RESEARCH to beat oilseed rape disease phoma suggests UK work could be worth stepping up.
With the UK government considering new guidelines for variety National Listing, more needs to be known about the fungus, which can lead to debilitating stem canker, says NIAB”s Simon Kerr.
Experiments by Euralis Semences plant breeders have found that the rapid breakdown to phoma by the formerly resistant variety Capitol was due to new strains arising.
These overcame the variety”s specific defence, which was based on a single gene, says ES”s EU area manager Jean de Walsche. “For three years Capitol had very good resistance to phoma. But then it suddenly became susceptible. That caused red lights” everywhere.”
Depending on variety and season, stem canker cuts French output by 5-20%. As a result, the French now encourage growers to avoid growing any single variety too frequently on the same field to limit the build up of such strains, he says.
Whether similar resistance-busting strains yet exist in the UK is unclear, notes Mr Kerr. “And with the possibility of sustainability becoming more of a factor in NL variety testing, a better understanding of the race structure of the canker fungus will become more important.”
Working with other breeders, ES has pinpointed two types of resistance. The specific type, characterised by the absence of leaf spotting in the autumn, is based on single genes, says ES”s Thomas Foubert. So far, nine have been identified, though some are no longer effective.
There is also a more general quantitative (QTL) type, displayed by old varieties such as Jet Neuf, where no major resistance genes are believed to be involved.
It is the latter which is thought to account, at least partially, for the particularly good stem canker defences displayed by newly HGCA-recommended variety ES Astrid in both French and UK trials, says Neil Groom of UK agent Grainseed.
“In CETIOM trials ES Astrid had no phoma leaf lesions in the field.” That mirrors the very low levels seen in HGCA work, he says.
CSL disease surveys show a steady rise in phoma infection in the past decade, particularly in the south-east of the country, where 60% of the UK crop is grown, notes Mr Groom.
Based on the standard 10% infection spray threshold that improved defence could be worth up to 20/ha (8/acre) to growers, he calculates.
Besides its good stem canker resistance, the variety is a stiff-stemmed, low biomass type.