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Breeders draw on multiple gene weapons in the fight against costly rust diseases

University of Sydney researchers have gathered a huge body of information regarding the genetics of different cereal rust pathosystems.
Photo: GRDC

Durable disease resistance is best achieved by incorporating multiple resistance genes in cereal cultivars. This has proven challenging for breeders, who have to package many important genes that go into making a new, superior cultivar.

The increasing availability of robust molecular marker diagnostics for important traits such as disease resistance is, however, increasingly expediting this process.

In the case of rust diseases, over time at Sydney University we have gathered a vast body of information regarding the genetics of the different cereal rust pathosystems through long-term annual pathogenicity surveys and genetic studies of cereal host resistance.

This has enabled the rapid and targeted application of many of the latest technologies to enhance the breeders toolbox.

For example, the recent availability of the barley reference genome and improved sequencing technologies have permitted very effective use of such information to rapidly identify the molecular basis of resistance to disease in crop species.

Utilising genetic information generated at the University of Sydney over the past 30 years on the leaf rust pathosystem in barley, we have initiated collaborations with researchers at the Institute of Experimental Botany (Czech Republic) and the John Innes Centre (UK), which co-invented a technique that rapidly unravels gene space in crops species.

The approach, referred to as MutChromSeq, relies on knowing the barley chromosome on which the resistance gene of interest is located, and generating gene-knockout mutants in a barley stock that carries the resistance gene using high-throughput rust testing in the greenhouses at the University of Sydneys Plant Breeding Institute, Cobbitty.

The target chromosomes are isolated from the normal and the knockout mutants using a process known as flow cytometry.

The sorted chromosomes are then sequenced, and bioinformatic analysis is used to hone in on the resistance gene by finding the single gene that is different between the normal and the mutant barley chromosomes.

This approach can theoretically be used for any trait that can be easily identified ('phenotyped') in any cereal crop, and is especially suited for complex polyploid genomes such as wheat or oats.

Using this approach, we recently identified the molecular basis for barley leaf rust resistance gene Rph1 and an uncharacterised recessive leaf rust resistance gene, both on chromosome 2H.

We are now generating/characterising mutants for multiple resistance sources with the aim of developing a molecular toolbox of gene-based markers.

The aim is to rapidly isolate as many genes with diverse mechanisms as possible, to enable breeders to better select gene combinations that are durable and can be implemented faster.

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