Enhanced suppression of 'Gaeumannomyces graminis' var. 'tritici' by retention of residues in a cereal cropping system

Abstract

The effects of stubble management and crop rotation on suppression of soilborne pathogens was studied in wheat cropping soils taken from established trials at Moree, Warialda and Croppa Creek in northern New South Wales, Australia. Biological resilience was evaluated in two ways? by measuring severity of take-all when the pathogen ('Gaeumannomyces graminis' var. 'tritici') was introduced to soil, and by assessing displacement of 'Fusarium pseudograminearum', the cause of crown rot of wheat, from buried straw pieces. No effects of stubble management or rotation with sorghum were found on suppression of either the introduced or resident pathogens at the Moree site. At Warialda and Croppa Creek, the severity of take-all in pot bioassays was significantly lower in soils from zero-tillage plots with stubble retained than in cultivated plots where the stubble was burnt. This effect was seen in soils from both continuous wheat and wheat–chickpea rotation treatments. There were no consistent differences between treatments in soil microbial biomass or respiration, or in soil carbon contents. Stubble retention also significantly increased the rate of displacement of 'F. pseudograminearum' from infested straw at Croppa Creek, but not at Warialda. The results showed that, at two out of three sites, retention of crop residues increased the ability of the soil to resist the effects of introduction of a major plant disease.