Australia's Grains Research and Development Corporation: The Crop Doctor

This year’s wheat yield is not just dependent on today’s conditions but cropping decisions over the past three years, according to new research into root-lesion nematodes (Pratylenchus thornei).

The microscopic eel-worms feed and multiply in the roots of crops, reducing yield by an estimated $50 million annually in the northern cropping region alone.

Research undertaken by the Queensland Department of Primary Industries and Fisheries and funded by the Grains Research and Development Corporation (GRDC) has looked at the influence of different crop rotations in land infested with Pratylenchus thornei.

It has found that the wheat varieties chosen during the four year trial had a significant impact on the nematode numbers and therefore yield, as did the choice of summer crop species in between.

John Thompson, Senior Principal Soil Microbiologist from the Queensland Department of Primary Industries and Fisheries, said that varieties within crop species are also important.

“Eradication of root-lesion nematodes is considered impossible and the industry is still working on resistant wheat varieties, so in the meantime minimising nematode numbers and the impact they have is vital,” Dr Thompson said.

“The other important finding from the research is that various crop species and varieties react differently to the two species of nematode found in the northern cropping region.”

The field trials were carried out with Kirsty Owen and Tim Clewett at Formartin, 70 km west of Toowoomba in Queensland.

The first year, high and low populations of root lesion nematodes (P. thornei) were established by growing susceptible wheat or a resistant canaryseed variety.

The following season, after eleven months of clean fallow, six summer crop species were planted on the prepared plots – 16 varieties of sorghum, 7 varieties each of sunflower, maize, millet / panicum and mungbean / blackgram and four varieties of soybean.

After another 13 months bare fallow, the entire site was planted with the wheat variety Strzelecki, which is P. thornei susceptible and intolerant.

Soil samples were collected immediately before planting and after harvest of the summer crops and before planting wheat to determine nematode numbers.

“Despite there being two periods of clean fallow, the populations of P. thornei in the soil profile remained high enough to pose a threat to susceptible wheat varieties,” Dr Thompson said.

The best yields of the wheat cv. Strzelecki were obtained on plots planted with canaryseed in the first year of the experiment then followed by sorghum, maize, sunflower or millet/ panicum in the following year.

The poorest yields of the Strzelecki wheat were obtained on plots planted with wheat in the first year of the experiment then followed by mungbean or soybean in the following year.

“Careful choice of rotation crops, extending over several years, is a practical and sustainable way to manage P. thornei and to maximise wheat yields,” Dr Thompson said.

“The research clearly shows that the choice of crops planted will have an impact on yield in later years.”

Peter Reading is the Managing Director of the Grains Research and Development Corporation