Western Australia
September 5, 2007
Canola breeders will soon know for
the first time exactly how host resistance in their varieties
responds to the fungal parasite that causes blackleg disease of
canola crops across Australia.
The most damaging disease of canola worldwide, blackleg caused
the total collapse of WA’s canola industry in the 1970s and
remains the number one threat to canola production.
The University of Western
Australia (UWA) Institute of Agriculture post-doctoral
researcher, Dr Hua Li said canola breeders and growers had not
known how the blackleg parasite overcame resistance.
“A sound knowledge of host resistance to this parasite would
certainly help canola breeders fast track breeding of more
resistant varieties.
“Discovering how blackleg infection occurs in stems will enable
them to select lines with improved resistance to stem canker,
which causes the collapse of canola stems. Maximum yield loss
occurs with infections initiated at an early seedling stage,
rather than later plant growth,” Dr Li said.
UWA researchers discovered differences in the parasitic spread
of the blackleg fungus in stems of Surpass 400, a canola variety
with single dominant gene-based resistance and also in the
polygenic resistant varieties Dunkeld, Grouse and Outback .
“Restricted blackleg invasion in the stems of all resistant
varieties was caused by cell fortification or lignification,
additional cambium formation and wound healing or suberisation,”
she said.
“Plant defence processes dramatically increased in resistant
varieties, with the reaction in stems of the most resistant so
fast that the disease stopped progressing within four to five
days,” Dr Li said.
While lignification and suberisation functioned as an additional
barrier to the invading parasite in all resistant varieties,
these processes occurred much more rapidly following infection
in varieties with major gene resistance, such as Surpass.
Cambium formation, where extra tissue layer production
compensates for parasite destroyed tissues, occurred faster than
the fungus could attack, providing additional protection in
resistant varieties.
“Surpass varieties were more resistant than Dunkeld, Grouse and
Outback , but this resistance often broke down within three
years because it’s based on a single gene,” she said.
“Polygenic resistant varieties are, therefore, much more durable
in the long term,” Dr Li said.
UWA Associate Professor Martin Barbetti of the Department of
Agriculture and Food WA and UWA Professor Sivasithamparam,
co-supervisors of the UWA and Grains Research and Development
Corporation (GRDC) supported research, said it showed potential
for selecting lines with improved blackleg resistance based on
the level of restriction to parasite spread within stems.
“The GRDC’s recent strategic plan for 90 percent of canola
entries in NVT with blackleg resistance scores of seven or above
by 2010 is an achievable target,” Professor Barbetti said. |
|