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Getting to the roots of disease

New assay detects fusarium in soybeans.


November 12, 2007
By Ralph Pearce


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30aIn 2002, Dr. André Lévesque unveiled some of his early findings
in a study of soybean root rot diseases and their causal agents. Two years later,
with much of the field testing complete, Lévesque, a mycologist with
Agriculture and Agri-Food Canada's Eastern Cereal and Oilseed Research Centre
(AAFC-ECORC) in Ottawa, has furthered his work in identifying and being able
to directly detect fusarium species in soybeans in eastern Ontario.

With the help of Dr. Tharcisse Barasubiye, another researcher with AAFC-ECORC,
Lévesque is poised to take the research in one or two different directions.
"We have a good number of isolates that have been tested for pathogenicity
through preliminary in-vitro tests, but the next step would be to look at representative
fusarium isolates that we have identified, and check further on their pathogenicity,"
he explains. The results are based on two seasons worth of work, in 2001 and
2002, covering 116 fields in eastern Ontario and Quebec, with 10 samples from
each field. "The isolates could also be used to screen soybean varieties
for resistance to the isolates that are linked to root rot."

Diseases do migrate
An interesting but disturbing finding from Lévesque's and Barasubiye's
work shows diseases like phytophthora are indeed moving east. In the past five
years, researchers, breeders and extension personnel have cautioned growers
that as the soybean producing regions continue to move across Ontario and into
Quebec, many of the diseases affecting southern Ontario are likely to show up
further east. This research provides further confirmation.

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"What we found in Quebec and eastern Ontario is that we start to see more
of the Phytophthora sojae which are commonly found in southern Ontario,"
says Lévesque. Another significant finding, more because of its absence,
is the lack of the fusarium species that cause sudden death syndrome. "But
then we have found other fusarium species and quite a few different ones, and
it's unfortunate, because it becomes a bit more of a challenge since quite a
few fusarium species appear to be pathogenic even though they are not the SDS
isolates."

Further down the road
Once researchers are done with more in-depth analysis of the isolates, there
is the potential for that genetic material to be passed onto breeders for use
in developing tolerance or resistance. Beyond that, there is an idea to modify
a diagnostic tool which has been recently implemented by the US Postal Service.

Worth roughly US$300 million in research investment, the system is a fully
automated DNA testing device which detects anthrax spores by sampling the air,
extracting any available DNA and running a PCR (Polymerase Chain Reaction) test
every 30 minutes on a non-stop basis. "This kind of technology is coming,
and I'm optimistic that we can sort of piggy-back on some of this," says
Lévesque. "We've developed a comprehensive set of DNA test protocols
but they are not in this kind of self-contained, automated format, but then
such a format could be easily modified once these technologies are more broadly
available."

Because of this project, it is now possible to provide to the breeders a full
profile of pythium, phytophthora, fusarium species present in their variety
screening plots using rapid assay. It will be available to growers as soon as
a laboratory is ready to provide a DNA-based diagnostic service to the growers. 

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