Wednesday, 5 September 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.

Media references

Associate Professor Martin Barbetti 61 8 6488 3924

Dr Hua Li 61 8 6488 2709

Professor Kadambot Siddique 61 8 6488 7012
0411 155 396

Simone Hewett / Sally-Ann Jones 61 8 6488 7977
(UWA Public Affairs) 0420 790 097 / 0420 790 098

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