Australia
March 19, 2012
Researchers are beginning to unravel the behaviour of a complex and damaging crop root disease known as Rhizoctonia, and finding new ways to manage crops to reduce its impact.
The disease is estimated to cost southern Australian grain growers nearly $60 million a year in lost productivity.
Grains Research and Development Corporation-funded research, carried out by CSIRO and other research partners, is outlined in a new GRDC fact sheet for the southern and western cropping regions – Management to Minimise Rhizoctonia in Cereals.
The latest insights into this difficult-to-control disease reveals that the soil fungus Rhizoctonia solani AG8 causes crop damage by pruning newly emerged roots. This can occur from emergence right through to crop maturity, resulting in water and nutrient stress to the plant. When severe, infection is seen as patches of poor crop growth.
Researchers are discovering how the environment and management practices impact on the levels of Rhizoctonia inoculum produced and the extent of infection in cereal crops in particular.
Dr Vadakattu Gupta, an Adelaide-based scientist with the CSIRO, is one of many cereal root disease experts who consulted with GRDC in development of the fact sheet.
Dr Gupta says Rhizoctonia root rot is difficult to control, for a number of reasons.
“The fungus can grow and survive in the soil in the absence of a live plant host, the fungus has a wide host range, there are no resistant cereals, and it is strongly influenced by soil and environmental conditions and therefore the seasonal impacts are difficult to forecast,” Dr Gupta said.
He said effective control of Rhizoctonia disease required both the reduction of the pathogen inoculum and control of infection process.
According to the fact sheet, levels of Rhizoctonia inoculums will be highest following cereals and lowest after canola and mustard. Experiments in south-eastern Australia have shown that canola and mustard provide effective breaks following cereal crops.
Other non-cereal rotations provide a useful reduction in Rhizoctonia inoculum, but not as reliably as canola or mustard; lupins may be a particularly poor break crop. The effect of a wider range of crop types is currently being investigated in southern and western regions.
Research reveals that rainfall events post-harvest cause a significant reduction in the inoculum and multiple rainfall events over summer and autumn can reduce inoculum levels to low risk.
At sowing, disturbance below the seed using narrow points is an effective method for managing Rhizoctonia in direct-drilled crops.
Dr Gupta said factors that reduced the rate of root growth would result in increased Rhizoctonia root damage; for example, cold soils, poor nutrition, compacted soils, and herbicide residues.
“Biological disease suppression has been identified in a range of soils and can also provide effective long-term control of disease,” he said.
This is leading researchers to try understand the basis of this suppression with the hope of being able to manipulate it in the future.
The fact sheet is being mailed to growers in the March-April edition of GRDC’s Ground Cover magazine. It is also available for viewing and download via
www.grdc.com.au/GRDC-FS-RhizoctoniaSW.
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