We are not making the most of varietal resistance in the battle against Septoria tritici, says HGCA Recommended List manager, Jim McVittie.
A few years ago, the best RL variety rating was a 6. Now it is 7, thanks to Robigus, Gatsby and Alchemy; well, almost.
They are rounded off from 6.5 and 6.8. Not groundbreaking, Dr McVittie acknowledges, but with the loss of strobilurin activity and increased insensitivity to the triazoles, every decimal point on the scale counts.
“Our target should be a rating of 7.5.
If this could be combined with reasonable resistance to other diseases, it would reduce the difference between the treated and untreated yield on the Recommended List to below 1t/ha.
ADAS estimates this would make any further increase in fungicide sensitivity much more manageable.”
But breeding for septoria resistance is not easy.
In almost all cases, the few genes of major effect identified in the UK have proved ineffectual.
Instead, plant breeders are using minor genes each giving only small effects, which need to be “stacked” in a variety to give good resistance.
Since each offers such a small effect on overall disease resistance, they are not easy to find, which is why a DEFRA Sustainable Arable LINK project is trying to find potentially useful genes and markers so they can be tracked in breeding trials.
Complicating selection is that most high yielding wheat varieties generally are the most susceptible to septoria.
But the project has pinpointed a small group of varieties with genes that increase yield, but do not reduce resistance to septoria, and trials to investigate their value are now in progress.
The study has also identified genes on six wheat chromosomes with increased field resistance to septoria.
The most resistant variety in use has only four of these genes.
Dr McVittie is hopeful we can exploit the others, which may allow growers to save money by using just one or two low-dose septoria sprays.