'Gene sandwich' enhances wheat rust resistance

COMPARISON: A side-by-side comparison of the rust protection in action, right, and unprotected wheat. Photo: University of Minnesota

COMPARISON: A side-by-side comparison of the rust protection in action, right, and unprotected wheat. Photo: University of Minnesota

Australian farmers are expected to produce a strong wheat crop this year, yet that would be threatened if a large outbreak of wheat rust occurred.

Researchers at the CSIRO have led an international effort to develop wheats with a stronger and potentially more durable level of resistance against rust diseases by 'stacking' five resistance genes together.

This represents a major advance over conventional wheat breeding protocols where individual resistance genes are added one by one.

The researchers developed novel genetic technologies that combine and insert the five genes together, with the bundling preventing separation in subsequent breeding generations of the plant, according to results published in Nature Biotechnology.

Lead CSIRO researcher Dr Mick Ayliffe said this novel approach of building multiple layers of protection would make it harder for rust pathogens to successfully attack wheat.

"Our approach is like putting five locks on a door - you're making it very difficult to get in," he said.

"Rigorous field testing showed that our gene stack approach provided complete protection against the rust pathogens we were targeting.

"Successfully validating the effectiveness of our technology makes this approach an incredibly attractive opportunity to protect global grain crops."

Australia's $6 billion per annum wheat industry supports more than 170,000 jobs and it is estimated a disease outbreak of one of the world's most virulent strains of rust - Ug99 - could cost the industry up to $1.4b over a decade.

With rust a global problem, the CSIRO has collaborating with international researchers from the University of Minnesota, Aarhus University, The John Innes Centre, USDA, Xinjiang University and strategic funding by the 2Blades Foundation.

Dr Ayliffe said this study had targeted stem rust, but the technology could also be used to breed against stripe and leaf rust diseases, and in different existing wheat varieties to add resistance.

"One of the genes we selected actually protects against stem, leaf and stripe rust diseases, so it's entirely possible to include genes that also work against other rust species," he said.

"We don't know the limits of this new gene stacking technology yet. We currently have an even larger genetic stack with eight resistance genes in the lab, so even more protection against rust is possible."

Wheat rust can rapidly mutate, making it difficult for wheat breeders to respond quickly using conventional breeding.

However, multiple genes compiled together in a gene stack could greatly strengthen the wheat and be deployed far more quickly.

Adoption of this new in-built resistance technology would also be a valuable tool for integrated pest management, lowering the need for fungicides and increasing the durability of the management tools for farmers.

Further advances in this technology are now allowing the researchers to explore building new gene stacks that would not be considered genetically modified and would ease their broad on farm deployment.

Rust spores are transported by wind, so international adoption would help to reduce the risk to Australian grain crops from exotic incursions from overseas.

"This promising gene stacking technology is a way we could rust-proof not only Australia, but international crops as well," Dr Ayliffe said.

"It's a valuable insurance policy in case we face mutations in wheat rust with catastrophic virulence, with the ability to deploy long-lasting solutions to the field much sooner than we would have in the past."