Australia
November 19, 2008
Necrotrophic diseases of wheat,
such as yellow spot and Stagonospora nodorum (also known as
Septoria and glume blotch), kill plant host cells and cost
Australian growers at least $170 million per year.
But recent research offers a way to improve wheat resistance
breeding.
The Grains Research and
Development Corporation (GRDC) supported Australian Centre
for Necrotrophic Fungal Pathogens (ACNFP) at WA’s
Murdoch University has
established major research programs to define mechanisms of
pathogenicity and plant disease resistance.
 Professor
Richard Oliver, ACNFP Director and GRDC Western Region Panel
Deputy Chair, along with his team at Murdoch, has discovered how
a special class of toxins produced by the pathogen, known as
host specific toxins (HSTs), are critical to the virulence of
this disease in wheat.
Unlocking the way HSTs are involved in causing disease has
improved understanding of wheat resistance and susceptibility to
necrotrophic fungal diseases.
Professor Oliver explained that HSTs are molecules toxic only to
the host of the disease and are mostly harmless to other plants.
Further, only specific genotypes, or forms of the host, are
sensitive to the toxin.
Professor Oliver and his team have demonstrated that the
pathogen Stagonospora nodorum, cause of glume and S. nodorum
blotch of wheat, interacts with its host via a specific and
complex set of HSTs which are encoded on separate genes.
Genetic analysis of the host has shown that, in most cases,
sensitivity to the toxin is a dominant trait in the host plant.
According to Professor Oliver, studying resistance to
Stagonospora nodorum has been complex, due to differing plant
resistance and susceptibility at the seedling, adult and glume
stages.
But the team has identified several HST genes carried by
necrotrophic fungal pathogens.
“One HST in the wheat pathogen, Pyrenophora tritici-repentis,
which causes yellow leaf or tan spot, is known as ToxA and is
identical to a gene in the genome of Stagonospora nodorum,”
Professor Oliver said.
Evidence suggests the gene has been laterally transferred from
Stagonospora nodorum to P. tritici repentis in the recent past.
“It appears that P. tritici is the recipient and Stagonospora
nodorum the donor, due to a process known as lateral gene
transfer, which is consistent with the finding that yellow spot
was unknown as a wheat pathogen before the 1940s.
“We therefore have a theory to explain how new diseases arise
and a way of improving disease resistance in wheat,” Professor
Oliver said.
“Isolated HSTs can be used to test wheat varieties for their
sensitivity to disease and provide wheat breeders with a new
tool to determine which varieties are resistant to necrotrophic
fungal pathogens.”
Professor Oliver said growers would then have new varieties more
resistant to some of the major diseases affecting wheat crops.
Further, they could choose to immediately avoid susceptible
varieties. Professor Oliver estimated this would save growers
$30 million a year and more in the future. |
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