The variety of winter wheat you choose to sow can have an impact on how much disease is going to be present in the crop, according to Teagasc’s Joe Lynch.

Lynch, a post-doctoral researcher, presented the latest research findings on varietal resistance in winter wheat at Wednesday’s Crops and Cultivation open day in Teagasc Oak Park.

The best way to judge a variety for septoria tritici resistance is through the use of the Department of Agriculture’s Recommended List. Varieties are rated from zero to nine – the closer to nine, the more resistant the variety.

In 2016, 90% of winter wheat sown was rated between four and six for septoria resistance.

“Most of the varieties that we sow are considered quite susceptible, with a four or five rating,” Lynch said.

Only 10% of winter wheat varieties sown had a rating of seven – the highest resistance rating available to us.

Varieties with a resistance rating of eight are not commercially viable at the moment, as they fall down in other key areas; these include either poor yield or grain quality.

However, for Lynch’s research, a variety with a resistance rating of eight was included. The study aimed to evaluate the benefits gained from selecting varieties with higher septoria resistance.

Benefits of selecting for resistance

Lynch found that selecting for septoria resistance reduced disease pressure in winter wheat crops. There was a 30% difference in septoria severity between varieties rated four and seven.

Between varieties rated four and eight, there was a 73% difference in the level of septoria infection.

“If you reduce the incidence of disease in your field, you are reducing the strain on the fungicides you are using,” he said.

When weather is poor and it’s difficult to apply fungicide, Lynch explained how this will lead to septoria in the crop and a subsequent yield hit.

The study found that varieties available to us currently, ranging from four to seven in resistance rating, show similar risk of yield losses when untreated. Varieties with higher resistance ratings can still incur high yield losses if protection is poor.

“You get a big hit on the most susceptible variety, but you also get a big hit on the resistant variety.

“The reason for this is because the resistant variety still gets some disease, which can do a lot of damage to the yield.

The varieties that we have still require good fungicide programmes to maximise their margins.

Very resistant varieties (rating of eight) were found to reduce the risk of yield losses.

The most beneficial aspect of a very resistant variety, according to Lynch, would be the potential reduced optimum rate of fungicide.

The very resistant variety has a lower requirement for fungicide and it consistently gets the highest margin at a reduced rate.

Resistant varieties – now and in the future

Lynch commented on the ongoing work being carried out in Oak Park. A number of people are trying to develop a high-resistant, commercially-viable variety, he added.

Lynch’s research shows that if a commercially-viable, high-resistant variety does come down the line, it will allow for:

  • Reduced disease incidence;
  • Reduced risk of yield losses when untreated;
  • Reduced requirement for fungicide.

Reliable varieties with a high septoria resistance would be very valuable for winter wheat production in Ireland, Lynch added.

However, with the range we have at the moment, selecting for resistance can improve the level of septoria infection in a crop only, and most varieties still require high levels of fungicide.

Selecting a variety with a higher resistance rating is proven to reduce the level of septoria incidence in your crop.

Lynch emphasised the importance of this finding for the sustainability of fungicides; reducing the pressure on the crop; and reducing the spread of disease through the crop.