Key points

• Research has identified sources of resistance to Sclerotinia stem rot in canola germplasm
• A breeding technique called genomic selection can be utilised to introduce Sclerotinia stem rot resistance into canola cultivars
• Research has found no correlation between the presence of spores on petals and disease incidence and severity

Successful control of Sclerotinia stem rot – a destructive fungal disease of canola and pulses – is highly dependent on the timing of fungicide application. There are no commercial Australian canola cultivars with resistance to Sclerotinia.

To help growers find more reliable ways to protect canola crops, GRDC investment in the Centre for Crop and Disease Management (CCDM) at Curtin University is targeting improved genetic resistance in canola cultivars, and management solutions that are adapted to Australian conditions.

Genetic resistance

CCDM researchers have screened a large canola germplasm collection (218 plants) and identified lines with partial stem resistance. These lines are now a vital resource for Australian breeders seeking to improve Sclerotinia resistance in future canola varieties.

Unlike most other diseases, resistance to Sclerotinia in canola is controlled by multiple minor genes acting together to provide resistance. This means that the classic marker-assisted breeding typically used to screen for major gene resistance for other diseases will not work for Sclerotinia resistance.

Instead, CCDM researchers have been the first in the world to apply genomic selection to estimating Sclerotinia resistance scores in canola. While marker-assisted selection relies on identifying one small section of DNA, genomic selection is based on the identification of much larger sections of DNA. The technique is essential to rapidly and efficiently breed quantitative ‘multi-gene’ traits into crops.

Such genomic selection can help identify the varieties most likely to carry Sclerotinia resistance for further evaluation and screening.

To progress this Sclerotinia resistance into Australian canola varieties, the CCDM is now providing seeds of resistant canola parent lines to Australian breeding companies, along with statistical and disease expertise.

Dr Toby Newman and Dr Mark Derbyshire measuring stem lesion length of flowering canola plants that were inoculated with an agar plug containing Sclerotinia sclerotiorum. Photo: Yuphin Khentry

Management solutions

A better understanding of the conditions that lead to Sclerotinia stem rot in canola in Australia is also important to help growers manage the disease.

Current Sclerotinia disease forecasting methods are based on research in Europe and Canada where crops are grown over a summer growing season under cool temperate climatic conditions. This means they may not be appropriate for canola grown in southern Australia during the winter under warm temperate conditions.

To determine the parameters that are required to develop and improve disease modelling for the Australian environment, disease incidence and severity were studied at 25 field sites across the Western Australian grainbelt over four years.

While spores from infected petals are known to be the dominant source of infection, testing of petals collected from the field sites for the presence of Sclerotinia spores showed no correlation between the presence of spores on petals and disease incidence and severity. This means that spore testing of canola petals is not recommended to help determine fungicide spray requirements.

Fungicide treatment at 30 per cent flowering did reduce infection levels compared with unsprayed plots; however, this did not translate into significant differences in yield. Further research is underway to determine what level of Sclerotinia incidence is likely to produce a yield benefit from spraying at the recommended 30 per cent bloom.

More information: Dr Lars Kamphuis, 08 9266 2606, lars.kamphuis@curtin.edu.au