BRENDON CANT brendon at iinet.net.au
Wed Sep 5 06:01:18 CEST 2007

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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


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.

HYPERLINK "http://www.fnas.uwa.edu.au/"www.ioa.uwa.edu.au

Authorised by ‘Institute of Agriculture – UWA’ and issued on its behalf by
Brendon Cant & Associates, Tel 08 9384 1122

MEDIA CONTACTS: Associate Professor Martin Barbetti, Tel 08 6488 3924,

Dr Hua Li, Tel 08 6488 2709, Professor Kadambot Siddique, Tel 08 6488 7012,
Mobile 0411 155 396




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