Evidence of biological suppression of Pratylenchus thornei in the northern grain region of Australia

The root-lesion nematode (RLN) Pratylenchus thornei is a major pest in the northern grain-growing region of Australia, costing the wheat industry alone $38 million/year in lost production. Current research is focussed on control of P. thornei by breeding tolerant and resistant varieties and using resistant hosts in crop sequences. Biological suppression of P. thornei is being examined as another potential method of reducing populations. To this end, soils from several farms across southern Queensland were sampled to examine whether suppressiveness was present using laboratory and pot assays. The laboratory assay incorporated ten day incubation of Radopholus similis in heat sterilised or unsterilised soil and measured nematode survival. The pot assay used wheat cv. Sunvale grown for 16 weeks in soil that had been heated (steam pasteurised), unheated or heated +10% unheated soil, and measured P. thornei reproduction. The laboratory assay consistently showed biological suppression of RLN occurred. For all soils, 10–39% fewer R. similis were recovered from the unheated soil than from the heated soil. In the glasshouse pot assay, populations of P. thornei increased only 2–8 times in unheated soil compared with a 17–32 fold increase when the soil was heated. The addition of 10% unheated soil to the heated soil reduced multiplication rates by 60-89%. Additionally, we did not detect differences in suppressiveness between soils growing crops, pastures or native vegetation. Further research is focussing on the specific antagonists that may be contributing to this suppressiveness and how they might be influenced by agricultural practices.