Scientists in Australia and overseas are unravelling the role of brassica plants in combating soil pests and diseases in other crops.
Soil-borne pathogens cause losses of $255 million each year to the Australian wheat industry.
'Biofumigation' research describes the use of compounds, naturally released from brassicas, to control disease in cropping systems. Chemicals known as glucosinolates (GSL) found in all brassica plants release biocidal compounds called isothiocyanates(ITC) into the soil.
CSIRO Plant Industry scientist John Angus recognised the potential benefits of brassicas when he found wheat grew better following canola and Indian mustard than it did following other 'break' crops such as linseed or oats.
Key research results to date have shown the following. An ITC released by brassica roots is highly toxic to cereal fungal pathogens. CSIRO studies found the compound could suppress take-all in glasshouse and field situations. The best fumigation results were observed in dry summers, and canola was more effective than linseed. CSIRO, in collaboration with departments of agriculture in each state, is continuing research into other soil-borne pathogens and will also be looking at any impact on the 'good' soil organisms.
Brassica weeds (wild turnip) in pasture can suppress take-all in following wheat crops. David Roget of CSIRO Soils warns that this may need to be taken into account when sampling soil for take-all.
Indian mustard sown into grassy pasture reduced take-all in the soil. Experiments at CSIRO Soils showed that the mustard reduced take-all infection from 54 per cent to 15 per cent. Harden (NSW) farmers found fodder rape sown into barley grass resulted in low levels of take-all in following wheat crops.
Concentrations of GSLs in Australian canola lines can vary up to tenfold, providing opportunities to breed varieties with better fumigation potential.
Root lesion nematode (RLN) numbers decreased dramatically following canola crops in a three-year study at the Waite Campus of the University of Adelaide. Other brassicas showed a similar ability to suppress nematodes.(See separate story this page.)
State-of-the-art systems at the John Innes Centre in Norwich, UK, measure ITCs released from brassica plant tissues. Working at the Centre under a GRDC Senior Fellowship, CSIRO Plant Industry scientist John Kirkegaard was able to compare the suppressive potential of Australian canolas with brassicas from England, Canada and Germany. During his attachment to the Centre Dr Kirkegaard also investigated the potential to genetically manipulate root glucosinolates to enhance biofumigation potential, and gained experience in latest techniques for ITC analysis and genetic modification of glucosinolates in brassicas.
Scientists are also investigating the possible negative impacts on beneficial organisms such as mycorrhizae and rhizobia. Concerns about poor legume growth following canola have prompted these studies.
In addition there may be toxic effects on seed germination, which may reduce weeds in summer following canola, but can also cause poor germination in a following wheat crop under some conditions.
Growers through the GRDC have supported a further three years' research to allow testing of the biofumigation concept in a wider range of environments and against other pathogens. The team will also look at possible impacts on beneficial organisms and weeds. A Postdoctoral Fellow has been appointed and will commence work in January 1999.
Some brassicas are more equal
The brassica family includes a range of crops such as canola, fodder rape, mustard and turnips, and some weeds such as wild turnip. While the role of brassicas as a disease break is generally recognised, their effectiveness varies.
Current research by John Kirkegaard and colleagues at CSIRO, much of it supported by growers through the GRDC, is directed at establishing which species or cultivars carry the highest levels of GSL, and are most effective against the various fungal and other pathogens. From the farmers' point of view, it is also important to decide whether biofumigation is the main aim or whether biofumigation is to be a bonus from a crop grown for oilseed or forage.
North, South, West