New fronts are opening up in the long and complex scientific assault on the cereal disease crown rot, which costs Australian graingrowers an estimated $56 million a year.

Stephen Simpfendorfer, Tamworth based pathologist with NSW Agriculture, told advisers and growers at Grains Research Updates in Dubbo, Nyngan and Narrabri the Grains Research and Development Corporation (GRDC) had brought seven projects together in a Strategic Initiative on crown rot, common root rot and Fusarium head blight.

Dr Simpfendorfer said scientists from NSW Agriculture, Queensland's Department of Primary Industries, the South Australian Research and Development Institute, CSIRO and the Universities of New England, Sydney, Western Sydney, Queensland and Southern Queensland were collaborating on the initiative.

The NSW Agriculture team at Tamworth was concentrating on disease management, with the effects of rotations on crown rot and their interactions with soil biology being a major thrust of the research.

"Trials at Tamworth showed brassica crops were generally more effective than chickpea in reducing the severity of crown rot in following wheat crops ­ more so in the susceptible durum variety Yallaroi than in the partially resistant bread variety Sunco," Dr Simpfendorfer said.

"But there was no evidence to suggest that higher levels of chemical compounds called isothiocyanates (ITCs) released from the taproot of
brassicas ­ and capable of biofumigation effects ­ reduced survival of the
crown rot fungus in stubble, or the severity of the disease in following wheat crops.

"The breakdown rate of crop residue ­ on which the crown rot fungus survives ­ is directly related to microbial activity, which is itself dependent on soil moisture and temperature.

"NSW Agriculture trials at Tamworth have found that residue breakdown is faster under break crops with denser canopies ­ the brassicas, faba beans, or sorghum in summer ­ than under a crop like chickpeas, which do not close over until later in the season.

"It is believed the denser canopies provide a more conducive environment for microbial breakdown."

Dr Simpfendorfer said measurements of wheat stubble cover following various rotation crops in 2002 showed remaining stubble cover to be greatest after wheat (85%), then chickpea (40%), canola (29%) faba beans (27%) and lowest following sorghum (15%).

Further research found higher levels of trichoderma ­ fungi commonly associated with the biological control of plant pathogens ­ in wheat following brassicas than in wheat following chickpeas or cereals.

Laboratory experiments had shown wheat plants colonised by trichoderma totally excluded the crown rot fungus. But others found that the fungi needed three months, at a temperature of 30 degrees, in moist soil, for best displacement of the crown rot fungus. They were not likely to get that in many years.

This season NSW Agriculture was establishing a new trial at Tamworth to spray trichoderma onto cereal stubble under various rotation crops, believing the crop canopies would provide a microclimate conducive to the activity of trichoderma and hopefully improve the efficiency of break crops in managing crown rot.

Research with trichoderma, and its potential to help stubble breakdown, was also being carried out in other areas, including some work under the GRDC's Eastern Farming Systems project on the Liverpool Plains, where the major problem was stubble loads after big grain crops.

"Managing stubble, and finding a balance between its positive role in conservation farming and its negative one in hosting the crown rot fungus, will be the key to eventual control of the disease," Dr Simpfendorfer said.

"Recent work by the University of New England has shown that stubble carrying the crown rot fungus has to be in direct contact with the growing cereal plant to initiate infection. A gap as small as two millimetres can prevent infection,

"Hence we're looking at the potential of trash whippers ­ which have been used to move cereal stubble away from germinating canola plants ­ to do the same thing for cereals.

"We are interested in what effect this may have on levels of crown rot infection."
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