University of Sydney provides update on science behind cereal genetic rust protection

Variety choice and devising control strategies are achieved with the best available knowledge of variety resistance.

These tables are regularly updated and are available via the University of Sydney Cereal Rust Plant Breeding program, led by Professor Robert Park.

Understanding the resistance status of these diseases is no easy task.

Multiple genes can be involved in a given disease. Some of these genes provide whole of plant resistance (from seedling to maturity), while some only provide adult plant resistance.

Adding to the complexity is that new strains of each disease periodically occur.

These can be mutations occurring locally within Australia or can be strains imported, either accidentally or via wind currents from overseas.

Because of the diverse genetic mix of many of our varieties, generally, at least some varieties are resistant to newly emerging or arriving rust strains.

Such advancement in protecting our cereal varieties from these potentially devastating diseases is no accident.

Decades of accumulated research, led by the University of Sydney's Cereal Rust Group at the Plant Breeding Institute, has developed technology to efficiently identify resistance genes and incorporate them into genetic material suitable for plant breeders to incorporate into commercial varieties as soon as possible.

The more resistance genes that can be included in one variety of all three rust diseases, the longer their resistance is likely to be.

Because of the periodic emergence of new rust strains, the search for new resistance genes is an ongoing requirement.

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Many sources are used by the PBI for finding new genes. These include wild types from distant relatives of wheat from various overseas locations, plus screening and cooperating with other breeders across the world.

Australia, recognised as a world leader in rust research, is commonly where many of these genes are first identified and incorporated into breeding material.

Farmers and agronomists are part of the ongoing nationwide annual surveys of virulence of cereal attacking rust pathogens and are rated by the PBI as a critical part of monitoring and predicting variety responses to rust diseases, as well as providing direction for resistance breeding.

For example, new strains are picked up by ongoing surveys and what strains are active in a given year and area help decide if fungicide treatment is likely to be necessary.

An example of the value of surveillance is the commonly occurring changes that have been documented in the stripe rust pathogen population.

The two most common current strains now are 239 and 198, which were first detected in 2017 and 2018, respectively and originated outside Australia.

Because some varieties are resistant to 198 but susceptible to 239, an increased frequency of 239 means that while some varieties displayed resistance in 2020, they were more susceptible in 2021.

Examples are Catapult, Coolah, Flanker, Rockstar, and Vixen.

These carry resistance genes that protect against 198 but not 239.

Adding to the confusion is that some varieties are more vulnerable to 198 than to 239.

For example, Bennett, Trojan and Borlaug 100, and to a lesser extent Devil, Illabo, Darwin, Emu Rock and Hatchet CL Plus. Also, 198 is a greater threat to several durum, for example, Artemis, Bindaroi, Lillaroi, Spes, Vittaroi and Bellaroi.

Resistance to rust pathogens in cereals can be expressed at all growth stages from primary leaf emergence onwards.

All Stage Resistance or seedling resistance, regarded as major gene resistance or as post seedling growth stages only, is termed Adult Plant Resistance.

Adult resistance genes commonly exhibit significant rust prior to their resistance taking effect as plants develop.

Visit www.sydney.edu.au/agriculture/our-research/plant-production.html

Next week: Fertiliser is not a dirty word.