New molecular techniques should make it easier for plant breeders to successfully design wheat and barley varieties with durable disease resistance in the future, according to seed specialist Nickerson.

Technology, such as molecular markers that make it easier to spot and transfer resistance genes, is rapidly increasing the understanding of the basis of resistance in varieties, the firm’s plant pathologist Paul Fenwick says.

“We’re using it to tease apart how it works.”

An example is the yellow rust resistance found in winter wheat variety Claire.

Rated a nine on the HGCA’s Recommended List its resistance has been extremely durable, despite being widely grown for several years in conditions favourable for yellow rust infection.

The new technology is making it easier to identify the genes providing the resistance, so they can be bred into “sons of Claire”, Mr Fenwick says.

Part of the reason for Claire’s durability is because it doesn’t confer complete immunity, senior wheat breeder Bill Angus says.

“It gets what we call unhappy yellow rust; it looks dull and dries up quickly, doesn’t go anywhere.

It is actually the varieties that never get a pustule you have to be careful with.”

That’s because their resistance is usually based on a single major gene, rather than a complex of genes, such as in Claire, Mr Fenwick explains.

“Working with single major resistance genes is easier, but if it is overcome it can lead to major breakdowns.”

The firm purposely avoids selecting plants with complete immunity to any disease during the breeding process.

“It’s dangerous.

If the parent breaks down any derivatives carrying that specific gene will go too,” Mr Angus says.

Adult immunity

Instead the firm selects seedlings which show some susceptibility to disease, but have high levels of adult immunity.

“We want varieties with resistance of the tried and tested type rather than the too good to be true,” notes Mr Fenwick.

For growers it is not always easy to know whether varieties on the Recommended List with a nine rating for disease resistance are based on single gene resistance, and therefore more at risk of breaking down, Mr Angus admits.

“The onus is on the breeders to explain the risks.”

But the Recommended List should carry more information for growers about whether the resistance is considered to be durable, he suggests.

That could be in the form of a high, medium or low risk rating for the break down of resistance.

“We’re close to being able to do that now [because of the technological advances], although there would still be quite a lot of don’t knows.”

mike.abram@rbi.co.uk