Soil suppression leads to nematode egression
The battle against root lesion nematodes (RLNs) is going to ground with new research suggesting suppressive soils can provide an effective defence against the parasitic pest which costs Australian grain growers more than $250 million annually.
A four-year research project jointly funded by the Grains Research and Development Corporation (GRDC) and Queensland Department of Agriculture and Fisheries (DAF) has assessed the level and variation of suppressiveness in northern soils.
Each year in the northern region, susceptible wheat and chickpea varieties are impacted by RLNs (Pratylenchus thornei and Pratylenchus neglectus) with estimated yield losses of up to 50% and 20% respectively.
Boosting the natural suppressiveness of northern soils is rapidly becoming the new frontline defence to control, and eventually reduce, RLN populations when used in conjunction with a best practice integrated management program.
Practices such as the use of tolerant or resistant varieties, crop rotation, no-till, stubble retention and good farm hygiene are generally effective in managing RLN populations but costly losses can still occur.
Disease suppression relies on the vast array of organisms in soil to provide a biological buffering against pathogens.
DAF Senior Soil Microbiologist at the Leslie Research Facility in Toowoomba, Dr Nikki Seymour said in glasshouse assays, P. thornei increased only 2-5 times in unheated soil compared with 17 times when soil was heated prior to planting to eliminate the general soil biological community.
“The research has shown by incorporating a small amount of unheated soil into heated soil (10% unheated) during seeding, RLN multiplication rates reduced between 60-89%,” Dr Seymour said.
“This demonstrates that specific organisms in the soils contribute to pathogen suppression, and crucially we’ve found it is not a physical or chemical property of the soil per se affecting multiplication.”
Funded by the GRDC, the four-year research project investigated disease suppression across 26 different paddocks on over 70 sampling sites in the northern region.
The impact of farm practices on the suppressiveness of soils to RLNs was studied as part of the project with results showing that factors such as pastures in rotation had a limited impact on soil suppression.
While cropped soils were generally found to be just as suppressive as nearby native grassland or scrub, frequent tillage on cropped soils had significant impact on nematode multiplication.
“Growers practicing no-till, stubble retention practices and cropping when soil moisture allows are probably doing the best they can to enhance their suppressiveness in the top soil,” Ms Seymour said.
“Without these practices, we estimate that RLN multiplication would be significantly greater especially in top soils and therefore lead to much greater losses in productivity of susceptible crops.
“As RLNs multiply right down the soil profile, practical means of increasing soil biology through improving carbon deposits are needed to reduce multiplication further.
“Research in this project has identified specific antagonists of the RLN – including some for the first time – in our northern grain growing soils however more targeted research is required on how to measure and enhance of these organisms in our soil.”
Elise McKinna, DAF Media & Communication Officer
07 3087 8576
Sarah Jeffrey, Senior Consultant, Cox Inall Communications
08 9864 2034, 0427 189 827
GRDC Project Code DAQ00164