Latest stripe rust warning - what it means for NSW growers

The new Yr17 attacking pathotype of stripe rust discovered by the Plant Breeding Institute at the University of Sydney is unlikely to present a major problem for farmers in central and northern NSW this year, according to NSW Department of Primary Industries (DPI).

Until now the Yr17 gene has been a major defence against stripe rust in many popular wheat varieties grown in NSW, including Ellison, Marombi, Sunbri, Sunlin, Sunstate, Sunvale and Ventura.

“Growers should not be discouraged from growing these potentially vulnerable varieties of wheat this season, as there are a large number of unknowns that need to be considered,”  NSW DPI senior plant pathologist Dr Steven Simpfendorfer said.

“For the new pathotype to present a problem this year it needs to survive over summer on volunteer wheat plants in the restricted areas where it has been found. However, the adaptability of the new Yr17 pathotype and its survival in 2007 cannot be predicted.

“If there is any good news from this drought it’s that it has significantly reduced the opportunity for over-summer survival of all rusts.”

The new pathotype arose as a mutation of the ‘WA pathotype’, which is well adapted, widely distributed and responsible for the stripe rust epidemics that have plagued growers since 2003.

But this new pathotype has additional virulence to the Yr17 gene, which means growers can no longer rely on this gene to combat stripe rust, according to Dr Simpfendorfer.

“The simple message is Yr17 varieties will need to be carefully monitored during the 2007 growing season,” he said.

“Seed or in-furrow fungicide applications with these varieties are not recommended as there are too many unknowns. The money would be better saved for a timely in-crop fungicide application, if that is warranted later in the season.”

Of the 150 stripe rust samples submitted to the Plant Breeding Institute Cereal Rust Laboratory at the University of Sydney in 2006, only two samples from Coleambally in southern NSW and Horsham in Victoria were the new Yr17 pathotype. 

Dr Simpfendorfer said the new pathotype would need to build-up on susceptible wheat crops in southern NSW and Victoria then blow north to present a significant risk to central and northern NSW wheat crops in 2007.

“Even if this did occur, it is likely to start from a very low base, which means it is more likely to occur late in the season in northern crops when they are well advanced which would limit the impact on yield loss.

In southern NSW, if the new pathotype establishes, it is more likely to affect crops at earlier growth stages.

“Listed varieties which contain Yr17, now under threat from the newly discovered pathotype, may also contain other minor resistance genes and adult plant resistance genes.

“All Yr17  varieties currently have a high level of resistance to the ‘WA pathotype’ and while their ratings will drop under attack from the new Yr17 pathotype, some may still have adequate resistance while others may fall enough to require fungicide management.”

The recent discovery highlights the importance of submitting rust samples to the Australian Cereal Rust Survey throughout the season. 

As this case has shown, rust monitoring can often provide an early warning of the impact which can give a one to two year warning to industry to allow some capacity for response through variety choice or fungicide preparedness.