Rust: the social disease
GroundCover™ Issue: 123 | Author: Bob Freebairn
- Breeding for multiple gene resistance is the best way to protect Australian crops against rusts
- Growers sowing susceptible varieties increase the likelihood of new mutant rust strains being selected, which makes it harder for breeders to keep ahead of the disease
- Belonging to a strong international community working on rust diseases helps to ensure Australia has access to the latest available rust-resistance genes and breeding programs
“Rust strikes: $100 million Wheat Losses” and “Stripe Rust: Farmers Panic”. These were headlines in The Land newspaper published on 8 November 1973 and 29 September 1983. They illustrate the periodic devastation caused by the three wheat rusts: stem, leaf and stripe.
Professor Robert Park, director of the Australian Cereal Rust Control Program (ACRCP), and who has been involved in wheat rust research for over 30 years, regularly reminds us of the enormous risk to Australian wheat growers that the three rusts pose.
So big is the threat of rust to Australian wheat growers that the ACRCP not only has strong financial backing from the GRDC, but also works with international bodies such as the International Maize and Wheat Improvement Center (CIMMYT). Other partners in the ACRCP include the University of Adelaide, the New South Wales Department of Primary Industries and CSIRO. The ACRCP also works closely with Australian wheat breeding companies.
Such links have international as well as local benefits: for example, the early identification and control of stripe rust in central Asia.
The ACRCP team has also been a key contributor to the Borlaug Global Rust Initiative (BGRI), which was established following the threat posed by the wheat stem rust race Ug99. Its primary objective is to reduce the world’s vulnerability to wheat rust diseases. BGRI is named after Dr Norman Borlaug, winner of the 1970 Nobel Peace Prize.
International collaboration, strengthened by Australia’s reputation as having the best-regarded rust research program, ensures we are linked with international cereal nurseries evaluating cereal rust diseases as well as breeding programs.
Professor Park stresses that while fungicides can be used to control rusts, their timely use by every grower is an unrealistic expectation. There are shortages of operators in bad disease years, sometimes shortages of chemicals, lack of timely identification and often unsuitable weather for timely application. Fungicide control is not always an easy strategy for each of these diseases, with well-timed multiple treatments often necessary with susceptible varieties.
Professor Park emphasises that the best approach for adequately controlling stem, leaf and stripe rust is to develop and release varieties with multiple gene resistance to each of the diseases. This is what the ACRCP has concentrated on for the past 30 years, with considerable success.
Wheat breeding companies have generally worked closely with researchers from the ACRCP, although varieties have sometimes been brought in from overseas with inadequate resistance to one or more of the rusts.
Professor Park says that wheat rust (as well as other rusts in crops such as barley and oats) is a social disease. By which he means that if one grower grows a rust-susceptible variety and a disease outbreak occurs, spores from that infestation can lead to infection in a susceptible variety hundreds of kilometres away.
More importantly, the more rust-infected crops that occur from widespread growing of susceptible varieties, the greater the chance of new (mutant) rust strains occurring. Such incidents have occurred over the years, resulting in high-performing, successful varieties being consigned to the ‘not to be grown’ susceptible category.
A strong reason for staying close to overseas rust assessment programs is so Australian breeding programs can prepare for any arrival of an overseas strain. This can occur via wind or human contamination. Both scenarios have occurred in the past.
Professor Park and his colleagues aim to provide plant breeding companies with breeding lines that have multiple gene resistance to each rust disease. Single gene resistance generally provides a greater risk of breakdown from a new mutant rust strain. Lines with multiple resistance genes make it harder for new rust strains to overcome a variety’s resistance.
A wheat industry that aims to only grow varieties with at least adequate resistance is also an important part of keeping the nation’s wheat crop protected from rusts. The fewer susceptible crops that are grown, the lower the chance of resistance breakdown occurring.
Professor Robert Park,
GRDC Project Code US00067