How your farm samples help improve varietal resistance

Research programs are often asking for growers and advisors to send in disease samples to assist in their research, but how does this lead to more profitable varieties for you? How are your samples used by researchers to ensure new varieties have improved disease resistance?

The following article hopes to shed some light on how your sample helps improve varietal resistance, with examples in:

  • Yellow spot in wheat
  • Powdery mildew in barley
  • Rust in cereals

We have also provided information on when and where to send your samples to assist researchers in improving varietal resistance.

Stop the Spot

Stop the Spot is an initiative by the GRDC and Curtin University-supported Centre for Crop and Disease Management (CCDM), which calls on growers and advisors to send in samples of yellow spot disease.

With these samples, CCDM’s yellow spot research program aims to provide wheat breeders with tools to breed more resistant varieties. When samples are received the researchers extract DNA from the infected leaf to determine the presence of the yellow spot pathogen. They are then able to grow the pathogen out to select a pure strain of the fungus. The researchers then look for the genes in this pure strain which encode effectors (host-selective toxins), in simple terms – those genes which allow that strain of yellow spot to attack a wheat plant.

Once they find an effector, the researchers clone it from the genome. The protein of the gene is expressed and produced on a large scale and purified ready for the breeders. The breeders will receive the bulked up effector protein, and can then infiltrate the solution into their wheat seedlings. Within days, breeders will be able to see if their wheat lines are sensitive to the toxin, and if they are, they can discard them, only keeping the resistant varieties in their programs.

By infiltrating wheat leaves with effectors discovered by CCDM researchers, breeders can see tissue death on sensitive wheat varieties in less than a week.

By infiltrating wheat leaves with effectors discovered by CCDM researchers, breeders can see tissue death on sensitive wheat varieties in less than a week. Source: CCDM.

More information on what happens to your sample is available on the Stop the Spot website.

Barley Powdery Mildew

CCDM’s barley powdery mildew program uses samples from growers and advisors to keep better track of the disease and watch for the development of new pathotypes. They also ensure resistant barley varieties are retaining their resistance, and if not, they communicate any breakdowns out to growers.

When a sample arrives, researchers will take a sample of powdery mildew from the leaf, and grow it on a susceptible barley variety, to ensure the sample is healthy.

Meanwhile, researchers also grow Pallas barley lines. Pallas barley lines consist of about 20 different barley cultivars that are specifically bred to each hold a different resistance gene. Leaves of these barley lines are cut and placed onto agar plates, ready for powdery mildew infection.

Pallas barley lines on an agar plate, each with a different resistance gene, infected with a sample of barley powdery mildew. Source: CCDM

Pallas barley lines on an agar plate, each with a different resistance gene, infected with a sample of barley powdery mildew. Source: CCDM

Researchers then infect the Pallas barley lines with your sample of powdery mildew and score the level of infection. If the powdery mildew survives, then they know there has been a breakdown in resistance in barley varieties that hold that resistance gene.

Monitoring genetic resistance in varieties to a particular disease allows growers to feel assured that the variety they are growing will hold up its defence against the pathogen, and if not, there’s a research team ready to confirm the genetic breakdown and work on new resistant varieties.

The Australian Cereal Rust Survey

The University of Sydney has maintained a watchful eye on cereal rust populations in all Australian cereal growing regions every year since 1921.

These surveys have revealed that our local rust pathogens sometimes mutate and overcome resistance in barley and wheat. Occasionally, these surveys have also shown when new rust isolates are introduced from outside Australia, such as when Western Australia was hit with stripe rust in 2002.

The University of Sydney has also monitored rust isolates spreading over long distances, with one recent example of a new South Australian wheat leaf rust isolate spreading to all other Australian wheat growing regions in just 15 months.

The annual rust surveys have underpinned all resistance breeding efforts for better resistant cereal varieties. The information generated, and the rust isolates identified, have been used to:

  1. devise breeding strategies;
  2. indicate the most relevant isolates for use in screening and breeding;
  3. define the distribution of virulence and virulence combinations;
  4. allow predictions of the effectiveness/ ineffectiveness of resistance genes;
  5. issue advance warning to growers by identifying new pathotypes before they reach levels likely to cause significant economic damage.

These early warnings on the occurrence of rusts not only alert growers to resistance breakdowns, but also solicit help to resolve situations where rust has been reported on a particular variety.

For more information about the Australian Cereal Rust Survey, visit The Rust Bust website.

When should I send in a disease sample?

Researchers will be grateful for any samples sent in for analysis. But in particular, researchers are interested in samples of diseased leaves when:

  • Varieties have been rated as resistant, or
  • a fungicide isn’t doing the job as well as you think it should.

Where to send your samples to assist researchers in improving varietal resistance

[table “1” not found /]
Share this:

Leave a comment