Early last year, we wrote about the threat posed to Australian barley growers by the exotic barley stripe/yellow rust pathogen (BYR). This pathogen causes significant problems in barley production in some parts of the world, but fortunately it is not present in Australia.
Although closely related to the wheat stripe rust pathogen (WYR), which is very common in Australia, BYR is specialised to barley and poses no threat to wheat.
Despite the absence of BYR in Australia, we receive occasional reports of stripe rust in barley crops. These reports require prompt action because they could mean that BYR has managed to find its way into Australia.
Such an incursion would be expected to impact significantly on barley production because many Australian barley varieties are highly susceptible to this pathogen. Resolving the identity of any stripe rust found in barley crops as quickly as possible is therefore vital.
Several reports of stripe rust in barley crops were received from southern NSW last year. Rapid diagnostic DNA tests and greenhouse seedling assays both confirmed that the pathogen responsible was not BYR, but rather a stripe rust form different from BYR and WYR that researchers first detected in 1998.
Known colloquially as ‘BGYR’, this stripe rust form does not infect wheat and, while it can infect barley, all cultivars other than Skiff, Tantangara and Maritime have good levels of resistance to it.
The name BGYR derives from ‘barley grass stripe (yellow) rust’, so named because it is very common on wild barley grass weed species such as Hordeum glaucum and Hordeum leporinum.
Using whole genome sequencing, we have been able to show that BGYR also occurs in North America, where it has been isolated from triticale and from the grass species Agropyron cristatum. In the 23 years that BGYR has been in Australia, our work has fortunately failed to detect any increased adaptation to barley or wheat in this rust pathogen.
Ensuring that diseases such as stripe rust do not become a problem in barley in Australia requires a multi-pronged approach. Working with state-based cereal pathologists, agronomists and other stakeholders, the Australian Cereal Rust Control Program monitors the occurrence and identity of rust pathogens in Australian cereal crops as an early warning scheme, to inform resistance breeding efforts and to enable rust risk management.
We have also been working with the International Maize and Wheat Improvement Center (CIMMYT) in Mexico to screen Australian barley varieties and breeding lines for response to BYR for about 20 years. This has provided an understanding of vulnerability to the disease and is enabling the development of markers linked to BYR resistance that breeders can use to incorporate resistance without the need for disease screening.
As always, all stakeholders are encouraged to inspect crops and nearby weeds for rust diseases. If rust is found, please send freshly collected samples in paper only to the Australian Cereal Rust Survey, University of Sydney, Australian Rust Survey, Reply Paid 88076, Narellan, NSW, 2567.