The increasing use of PreDicta® B testing is being credited with decreasing turnaround times for researchers exploring soil-borne disease interactions, variety resistance traits and working to develop crop disease management practices.

The DNA-based soil testing service is able to provide a detailed soil biology profile without the need for lengthy laboratory testing.

Experience is showing it is able to accurately identify the cause or causes of crop growth constraints and is speeding up research into disease and pathogen interaction.

PreDicta® B was released in 1997 by the South Australian Research and Development Institute (SARDI).

It is delivered to growers via accredited agronomists who interpret the results and provide recommendations on management options to reduce the risk of yield loss.

PreDicta® B can test for most soil-borne diseases of cereals and some pulse crops, including:

• crown rot (cereals);
• Rhizoctonia root rot;
• take-all (including oat strain);
• Pratylenchus thornei;
• Pratylenchus neglectus;
• cereal cyst nematode (CCN);
• stem nematode; and
• blackspot (field peas).

The tests take into account crop rotation and present levels of the diseases to provide a disease risk assessment.

In 2018, PreDicta® B added a new test for sclerotinia, following the addition of the following new tests in 2017 for:

• ascochyta blight of chickpeas;
• yellow leaf spot and white grain disorder of wheat; and
• charcoal rot.

In the northern region, extra tests were added for:

• Phytophthora root rot of chickpeas;
• Fusarium stalk rot of sorghum; and
• arbuscular mycorrhizal fungi (AMF) associated with long fallow disorder.

Blindfolds removed

NSW Department of Primary Industries plant pathologist Dr Steven Simpfendorfer says that before the introduction of PreDicta® B testing, researchers were essentially "flying blind".

"Previously we may have been running a wheat variety trial and been suspicious of the cause of a reaction during the trials but it would go formally undiagnosed," Dr Simpfendorfer says.

"Today you can see from PreDicta® B test results there may be a high background level of a certain pathogen and we can work out that this variety is quite susceptible and suddenly the reaction makes a lot more sense."

Dr Simpfendorfer says PreDicta® B is used to background all of his field trial sites and this can dictate choice of location based on the need for a "clean" site or to target particular pathogens for in-depth studies.

He says the test allows more room in the budget for trial work as, without the test, the results that PreDicta® B reveal would require specialised researchers to be sourced and employed.

"PreDicta® B testing has allowed us to dabble in nematology, which we previously couldn't do without specialised identification skills with a sample under a microscope," he says.

"This is a great outcome for growers in that they're getting a lot more research done within a budget as it allows a lot more cross-discipline research to happen."

Generating efficiencies

Agriculture Victoria senior plant pathologist Dr Grant Hollaway runs a crop disease research program with a significant focus on root diseases.

He credits the use of PreDicta® B testing with enabling a large number of efficiencies in his projects.

"We used to go through the process of extracting live nematodes from soils where we would take soil samples and store them in a cool room and, over a period of several months, we would extract live nematodes," Dr Hollaway says.

When we harvested, we got yield losses of about 20 per cent and without this test we wouldn't have known what was happening or how to prevent it. - Agriculture Victoria senior plant pathologist Dr Grant Hollaway

"Our program is now much larger and we can get the results back, in some cases, in a matter of days."

Game-changer

Dr Hollaway says PreDicta® B is a "game changer" for the industry, giving researchers the ability to identify problems before they're seen in the paddock.

"We got results from a trial last year where we tested the trial site and knew from testing that we had yield-limiting levels of nematodes there, but I could not see any visual effects of nematodes at all," he says.

"When we harvested, we got yield losses of about 20 per cent and without this test we wouldn't have known what was happening or how to prevent it.

"Where farmers are trying to get yield improvements of five and 10 per cent, PreDicta® B can give them feedback that they can actually do something about."

Whole system approach

PreDicta® B testing forms an important part of CSIRO principal research scientist Dr Lindsay Bell's farming systems research for GRDC.

"We've been using PreDicta® B tests as one of our critical measures of both pathogen and other biotic components of the system to try and understand how different crop sequences impact on pathogen loads into the system and potentially beneficial biota," he says.

"Until PreDicta® B was available, it was hard and expensive to be able to analyse the biotic component of the system."

Dr Bell estimates that in one of his projects where research is being done into crop rotation and yield, about 1000 samples are sent off annually for PreDicta® B testing.

Dramatic dynamics

"We're seeing quite dramatic dynamics in something like root lesion nematode over a crop sequence, where in the past it would have been much more difficult to do that analysis and collect those samples without the DNA and PreDicta® B approach," Dr Bell says.

"In one of our years, we grew four different winter crops and we followed up with the same subsequent crop on each plot and experienced vastly different yield results.

"There was no evidence this result was associated with soil water or nitrogen constraints, but we had data that showed there were differences in root lesion nematode populations.

"Unless we had that data, we might not have been able to explore that interaction."

The PreDicta® B service is delivered through SARDI's Molecular Diagnostic Centre, a state-of-the-art facility capable of delivering high-throughput diagnostic testing to industry.

Investment in the Molecular Diagnostic Centre and the continued development of PreDicta® B are components of the GRDC-SARDI strategic research partnership.

More information: Dr Alan McKay, SARDI, 08 8429 2216, alan.mckay@sa.gov.au