Rust resistance is wearing a bit thin
WITH minimum disease standards set to be maintained, a shadow hangs over the recommendation of several yellow rust susceptible winter wheat varieties.
As samples continue to flood into NIAB, significant differences are emerging in the levels of disease seen in trials, says Rosemary Bayles, head of the UK Cereal Pathogen Virulence Survey at NIAB.
Although current findings (see chart) are provisional, ratings among varieties susceptible to the YR17 race are expected to change as well as diversification advice.
A key feature is the apparent difference in field development of rust in a variety like Reaper, rated 3 on the 1-9 scale, against Brigadier, says NIABs John Ramsbottom.
The latter, described by one agronomist as suicidally susceptible, has a resistance rating of 2, says Mr Ramsbottom.
Officially the minimum disease resistance standard for general recommendation of a variety is 3, a fact recently reaffirmed by the independent Cereals Trials Advisory Committee, he notes.
"Brigadier is really pulling away in terms of susceptibility," says Dr Bayles.
Until last year the two provisionally recommended varieties Equinox and Madrigal were completely YR17 resistant. But more recently they, and several list candidates, have succumbed in varying degrees to a new doubly virulent rust race designated V6+V17, she explains. So far this race has not yet appeared outside inoculated trials at NIAB.
For the moment Consort, Hereward and Spark, appear unaffected.n