Getting rust sussed by Eammon Conaghan

The field nursery at Carnarvon where breeding lines are being screened for stem, stripe, and leaf rust resistance.

EXPANDED EFFORTS are underway to enhance rust resistance and reduce disease pressure on the existing genetic defences of WA wheat varieties.

The introduction of an exotic stripe rust in 2002 and mutations in local stem and leaf rust strains have left previously resilient varieties prone to infections.

WA Department of Agriculture Plant Pathologist, Robert Loughman, said the sequence of recent changes had driven a new wave of preventative breeding activities.

"A multi-pronged strategy has been developed to incorporate genetic resistances in future varieties underpinned by a new three-cycle-per-year back-cross-ing program for rust resistance. New resistant material has been for crossing into local material this spring," Dr Loughman explained.

The accelerated back-crossing program will turn out rust-resistant versions of high-performing but previously susceptible advanced breeding lines.

For example, the Department is accelerating the back-crossing of WAWHT2248 in collaboration with the Australian Cereal Rust Control Program, at the University of Sydney, to develop a rust-resistant version for WA soft wheat growers.

Meanwhile, the GRDC has supported the Department's efforts to inject new sources of resistance, supplied by the Australian Cereal Rust Control Program, into its breeding program to broaden the resistance base of WA's germplasm for future variety development.

A combination of field and glasshouse rust testing has also been developed to maintain rust resistance in locally adapted material. Supported by growers and the Federal Government through the GRDC, a newly appointed technician conducted 10,000 rust tests earlier this year.

"Another key strategy is to incorporate multiple-gene adult plant resistance in future varieties, rather than rely on individual major resistance genes that can be prone to breakdown, so field screening in early generations is important to help accumulate those genes," Dr Loughman said.

"Breeding lines in field nurseries at Carnarvon, Manjimup and Wongan Hills are being screened for resistance to stem, stripe and leaf rusts and material lacking adequate resistance will be eliminated from the breeding program."

While susceptible material is being eliminated, resistant material is being fast-tracked for rapid release to growers. Accelerated seed increase over summer will reduce the cycle time and enable material to move quickly to field and quality testing.

Together with other accelerated breeding strategies, such as single seed descent, the program will produce rust-resistant derivatives for potential release.

For example, populations related to the widely adapted variety WyalkatchemPBR logo were recently streamlined through rapid single seed descent to develop improved combinations of rust resistance. The resultant lines are now undergoing resistance screening in field trials.