ROOT DISEASE: tackling underestimated Pythium higher rainfall scourge

Uninfected control wheat plants (left) compared with Pythium-infected wheat plants (right). Disease symptoms include reduced crop emergence (seedling damping-off), poor early vigour and reduced root density.

LIMITING THE increasing incidence of Pythium root diseases could increase grain yields by at least 10- 15 percent, particularly in higher-rainfall areas, according to recent paddock trial results.

Research in Australia and overseas indicates that Pythium is responsible for declining crop yields across a range o f environments - with more frequency and severity in higher- rainfall areas where conditions are more suitable for disease development.

A collaborative project, supported by growers and the Federal Government through the GRDC, involving CSlRO Land and Water and Wesfarmers Landmark is developing an integrated management package using fungicide applications, crop rotation and tillage systems to achieve long-term sustainable control of Pythium.

Pythium is fast-growing and highly pathogenic, often killing crop plants at the seedling stage (damping-off). Seedlings that survive have damaged root systems, resulting in poor early growth and reduced crop vigour

These early setbacks to crop growth and the ability of Pythium to continually re-infect growing roots cause significant yield losses later in the season.

Field trials show a way forward

Recent field trials with Pythium-selective fungicides clearly showed significant yield increases in canola (5-38 percent ), cereals (5- 18 percent) and pulses (5-35 percent ). (See table below.) These responses occurred across a range of climatic and soil conditions and were greater in the higher - rainfall regions or south-eastern Australia (greater than 350 mm annual rainfall ).

Yield declines? Consider Pythium

Pythium causes root rot in cereal. pulse and canola crops. Because of its broad host range, Pythium inoculum (mainly spores) can build up over phases of thc crop rotation, reducing the effectiveness of legume and canola crops as clisease breaks and causing significant yield declines in subsequent cereal crops.

At field sites in SA and NSW, researchers showed that soil-borne Pythium levels from the canola phase of the rotation were generally double that from the cereal phase. These increased Pythium levels then led to significantly reduced yields in the following wheat crops.

CSlRO research using DNA tests showed that soil populations of Pythium consisted of a mixture of different genetic types (genotypes) and that rotating the grain crop caused shifts in the genotypes of Pythium available to infect the next crop.

Being able to detect and mcasure Pythium levels in cropping soils. combined with knowledge of what crops they are most likely to affect and how their populations will change in response to disease management strategies, will help develop targeted crop rotations to minimise yield losses.

Genetic analysis of Pythium populations also showed limited dispersal of different Pythium strains (genotypes) between farms. These results have important implications for assessing long- term disease control methods ( for example, crop rotation and fungicide applications), as there would be limited opportunities for the spread of crop-adapted or fungicide-resistant strains between paddocks. It may he possible for farmers to manage Pythium diseases on an
individual paddock basis.

A new phase of the research will identify and measure the levels and effects o f Pythium in cropping soils in higher-rainfall areas (more than 350 mm annual rainfall ) of southern Australia. DNA markers will be used to determine how phases of the rotation cycle affect the abundance, distribution and disease severity of the fungi.

The research aims to develop a targeted fungicide application and crop selection package to achieve long- term Pythium control through the growing season and into the next rotation phase.

Program 4 Contact : Dr Paul Harvey 08 8303 8589 email Paul.Harvey@csiro.au

Field Trial Results

Region North, South, West