Researchers at Teagasc have confirmed that Irish strains of septoria are able to overcome a source of genetic resistance present in a range of near-market winter wheat varieties.

This was the conclusion of a study led by Teagasc crops researcher Dr. Steven Kildea and accepted for publication in the Plant Pathology journal.

Septoria blotch is the primary disease of the Irish wheat crop and requires chemical treatment to ensure the crops yield potential is realised, Teagasc says.

In 2020, unexpected levels of the disease were observed on a selection of winter wheat varieties in a number of locations – each with the cougar variety in their background – which has reported levels of septoria resistance.

As part of the Teagasc cereal disease surveillance programme, initial results confirmed the strains of septoria isolated from these varieties were able to cause significant levels of disease on cougar when tested under glasshouse trials.

“Cougar derived resistance has been included in commercial breeding programmes for a number of reasons, including its initial resistance to septoria. However, our work has now confirmed that this source of resistance is vulnerable to Irish strains of septoria,” Dr. Kildea explained.

“With upwards of 20% of the Irish winter wheat seed available for autumn 2021 expected to be made up of varieties bred from cougar, the implications of these findings are immediate,” he warned.

As well as being able to overcome cougar, these strains of septoria are also able to infect and cause high-levels of disease on a range of varieties bred from cougar.

Further investigation is ongoing to determine how widespread this virulence is within the Irish septoria populations.

These septoria strains are similar in fungicide sensitivity to the wider Irish Z. tritici population.

However, the risk is greatly increased in regions where septoria pressures is traditionally high, such as the south of the country.

Here, even with well-timed fungicide programmes, there is a concern that adequate disease control would not be achieved and growers should consider alternative varieties.

In areas of lower septoria pressures, such as the north-east, Teagasc is advising growers to be aware of the increased risk associated with these varieties and to develop disease control programmes accordingly.

This should include keeping to a minimum the area to which these varieties are grown; delaying their sowing as late as feasibly possible to reduce disease pressures; matching disease risk to fungicide choices; and ensuring the correct application timings for septoria control.

The study can be viewed here.