Research unearthing insights into costly soilborne disease
Author: Sharon Watt | Date: 08 May 2013
Research funded by the Grains Research and Development Corporation (GRDC) is making significant progress towards improving options for the management of Rhizoctonia bare patch disease, which is presenting as a potential threat to cereal crops this season.
The disease, caused by a Rhizoctonia solani fungus, occurs mainly in the low to medium rainfall regions of southern Australia where annual losses in wheat and barley yields are estimated to be around $59 million.
The risk of Rhizoctonia bare patch is potentially high this cropping season due to a dry spring last year and continuing dry conditions since then. A late break to the season and cold soils will heighten the risk.
It is a difficult disease to manage but research projects in South Australia and Western Australia, funded by GRDC and the SA Grain Industry Trust Fund, are shedding new light on why and how it occurs and what can be done to minimise its impact on crop yields.
Dr Alan McKay, of the SA Research and Development Institute (SARDI) Soil Biology and Molecular Diagnostics unit, says the current research program aims to improve disease prediction, reliability of existing control strategies and support development of new methods of control.
One of a number of researchers investigating Rhizoctonia occurrence and management options, Dr McKay said that while Rhizoctonia was generally considered to be a pathogen of seedlings and not greatly affected by rotation, results from current GRDC-funded projects had shown otherwise.
“Research has demonstrated that it in can attack crops throughout the growing season, and that it is affected by rotation, with cereals and grasses being the main hosts,” Dr McKay said.
“Grass-free canola, mustards, field peas, chickpea, medic pastures and fallow provide useful reductions in inoculums which can benefit the following wheat crops, increasing yields by between 9% and 47%.
“However, the reduction in inoculum lasts for only one season as Rhizoctonia builds up on the cereal roots during spring.”
Dr McKay said it was now known that disease severity depended on a combination of factors.
These include the level of Rhizoctonia in the soil, soil disturbance and nitrogen (N) levels at seeding, constraints to root growth (such as compaction layers, low temperatures and soil moisture) and activity of the soil biology community.
“Rhizoctonia can attack crop roots throughout the growing season. Damage is greatest when soil temperatures drop to around 10C and or root growth down the soil profile is restricted,” he said.
“Severe damage to seedling roots results in characteristic bare patches. Seedling damage can be reduced by sowing early and reducing constraints to root growth – ensuring adequate N and micro nutrients during tillering will help reduce losses from this damage.
“Damage to the crown roots is much harder to stop, but increasing seedling density can reduce the impact of lost tillers.”
Research into the effects of seeding equipment soil openers on the levels of Rhizoctonia during seedling establishment has also produced some interesting observations.
Inoculum levels along rows sown with knife points (high soil disturbance to 10cm) were much lower than those sown with a triple disc system with flat discs (minimum soil disturbance to 6cm). Levels in rippled coulter-sown plots with disturbance to 10cm were intermediate.
“High Rhizoctonia levels in the flat disc-sown plots help explain why Rhizoctonia is more serious with disc-sown crops,” Dr McKay said.
Ongoing GRDC-funded research will enhance understanding of the role of summer weeds and rotation crops, evaluate banding fungicides and improve disease prediction.
Further information on the disease is contained in the GRDC Rhizoctonia Fact Sheet, available for viewing and downloading via www.grdc.com.au/GRDC-FS-Rhizoctonia.
A detailed article on research into the influence of seeding methods on Rhizoctonia appears in the May-June issue of Ground Cover magazine.
Caption: Dr Alan McKay of SARDI’s Soil Biology and Molecular Diagnostics unit, pictured speaking at a GRDC grains research Update, says the GRDC-funded Rhizoctonia research program aims to improve disease prediction, reliability of existing control strategies and support development of new methods of control.
Alan McKay, SARDI
08 8303 9375
Sharon Watt, Porter Novelli
GRDC Project Code DAS00122, DAS00123, DAS00125, CSE00150