Barley crops with more resistance to powdery mildew

Discovered at the Centre for Crop and Disease Management (CCDM) – an Australian research centre with co-investment by the Grains Research and Development Corporation (GRDC) and Curtin University – the three adult resistance genes share new mechanisms for fighting the barley powdery mildew pathogen. They are the best hope yet of achieving long term resistance to the disease.

Powdery mildew

Powdery mildew is a challenging disease for Australian barley growers, especially in high-rainfall and humid weather conditions favoured by the pathogen and can result in substantial losses in quality and yield.

The pathogen readily mutates to overcome conventional resistance genes, while chemical controls are similarly rendered ineffective. Fungicide resistance to triazole class (Group 3 Dimethylation Inhibitors – DMI fungicides) is now widespread in areas such as southern Western Australia, where the disease has at times reached epidemic levels.

Resistance to powdery mildew

Led by Dr Simon Ellwood, the research team had noticed some barley lines were resistant to powdery mildew at adult stage but not as seedlings. “This led us to focus our research on adult barley plants, specifically in exotic lines and landraces that are not closely related to modern barley cultivars and which have a limited range of resistance genes to powdery mildew disease,” Dr Ellwood said.

While these exotic and wild types of barley are not ideal as grain crops, their desirable traits can be bred into elite barley lines, including the new resistance genes that are now identified.

The team searched for resistance in over 1000 exotic lines and wild relatives of barley from regions of the crop’s diversity in the horn of Africa, the Near East and Asia, accessed through the Australian Grains Genebank. Carrying out genetic mapping and multi-pathogen disease screening, the team discovered that not only were the exotic barley lines themselves diverse, so were their types of resistance.

Reduce the reliance on mlo

Dr Ellwood says they also appear to be broad-spectrum, showing resistance to all powdery mildew pathotypes tested. And they are each single genes which makes them easier for breeders to work with. The new genes will allow breeders to reduce the reliance on mlo, a broad-spectrum resistance that is the only current alternative.

“Breeders now have a set of options they can use separately or together in various combinations to build strong, multi-mechanism resistances into our Australian barley cultivars”, Dr Ellwood said.

The full research report can be read here.