Grains Research and Development

Date: 01.09.2001

Doubly resistant peas

Jenny Davidson (right) and technical officer Marzena Krysinka-Kaczmarek inspecting early breeding lines for powdery mildew.

Early screening may ensure that more pea varieties with dual resistance to downy and powdery mildew become available to growers.

The early-screening process was developed by Jenny Davidson and the Pulse Pathology team at the South Australian Research and Development Institute, SARDI. The researchers started with determining the right environmental conditions for the fungi to flourish.

Until recently no varieties with resistance to both downy and powdery mildew were commercially available, and growers were often caught unprepared for outbreaks, which develop rapidly in the right conditions.

The SARDI researchers, supported by growers and the Federal Government through the GRDC, manipulate pea lines early in their development to isolate those that are likely to succumb to downy and powdery mildew.

"For successful screening of downy mildew we have found that specific environmental conditions are essential," said Ms Davidson. This involved growing the seedlings at 8°C and at high humidity, which allows the downy mildew to become active and infect the plant.

Plants with less than 10 per cent coverage of the underside of the leaf and the stem with downy mildew are rated as resistant. Those with more than 70 per cent coverage are rated as susceptible.

Following the downy mildew screening, the same seedlings are transferred to the greenhouse and inoculated with powdery mildew.

"We found that this totally unrelated fungus is much less particular about the environment it requires for growth. Glasshouse conditions at 20°C are ideal for development of powdery mildew on pea plants," said Ms Davidson.

Again plants are rated for the level of disease coverage, but this time on the upper surface of the leaves.

"We are able to identify lines with complete resistance to powdery mildew — even more importantly, we can identify those with resistance to both the mildews," said Ms Davidson.

This year, 73 new lines from the South Australian and 250 lines from the Victorian pea-breeding programs will be put through the early disease-screening process.

Program 2.4.2 Contact: Ms Jenny Davidson 08 8303 9389 Email: davidson.jenny@saugov.sa.gov.au

Region North, South, West