Yield losses from Fusarium crown rot can be as high as 50 per cent in susceptible wheat varieties in moisture-limited farming systems in Australia.

While there is strong demand for high-yielding, well-adapted wheat varieties with acceptable levels of resistance and tolerance to crown rot, existing genetic sources have only been partially resistant and mainly found in poorly adapted genetic backgrounds.

That, however, is finally changing through the efforts of the University of Sydney, with the South Australian Research and Development Institute (SARDI), the University of Southern Queensland and CSIRO, which have significantly improved genetic resistance and tolerance to Fusarium crown rot in bread wheat. The advances have come from a 10-year GRDC research investment.

The team used two approaches – pyramiding multiple sources of resistance and tolerance into well-adapted genetic backgrounds, and developing reliable and repeatable phenotyping methods that could be used by commercial breeders to measure these characteristics.

New lines

By evaluating a diverse breeding population of 700 lines, the team confirmed eight genomic regions associated with resistance to crown rot in multiple environments, in chromosomal locations where resistance genes were previously reported.

This gave researchers the confidence to pyramid these genes into diverse agronomic backgrounds generating 70 lines with resistance and tolerance, which have now been made available to Australian wheat breeders.

Marker-assisted recurrent selection was also used to efficiently pyramid 48 minor target genes generating eight fully fixed lines that combine resistance and tolerance exceeding industry benchmarks.

These 78 breeding lines represent a significant genetic resource, displaying up to 65 per cent less disease than the most-resistant varieties available and, on average, yielding 112 per cent of the best industry standards under crown rot pressure.

Confirming the success of these genes in the field is critical to measuring their value. This research has also led to improvements to disease severity ratings and sampling strategies in combination with accurate statistics, significantly reducing the noise in the data and improving the accuracy of variety selection. Improved methods to measure the impact of resistance and tolerance to crown rot on yield mean that, for the first time, researchers were able to identify a strong positive relationship between disease severity and yield loss.

A new GRDC investment led by Australian Grain Technologies in conjunction with the NSW Department of Primary Industries and SARDI will bring these tools to Australian breeding programs. The project will deliver accurate and affordable high-throughput identification, selection and tracking of resistance or tolerance in crown rot germplasm across the country.

More information: Professor Richard Trethowan, 02 9351 8860, richard.trethowan@sydney.edu.au

Even though crown rot-infected barley crops do not show as many white heads as wheat, they suffer similar yield losses and can accumulate much-higher concentrations of Fusarium, the causal agent of crown rot.

With GRDC investment, CSIRO Agriculture and Food has identified four genetic loci that are likely to have a large effect on resistance and tolerance. Project leader Dr Chunji Liu says that each of these loci can reduce yield loss from crown rot by 30 per cent.

“However, when we combine these loci we have obtained breeding lines that can reduce yield loss by an average of about 50 per cent,” Dr Liu says.

For the first time, data has revealed that a reduction in fertile tiller numbers is the main cause of yield loss from crown rot in barley. The team will continue to identify resistance genes to improve disease management in wheat and other crop species.

More information: Dr Chunji Liu, 07 3214 2223, chunji.liu@csiro.au