About 80% of plant problems start with the root and soil, making research into root health essential if the challenges of food security and sustainability are to be met.

“We need to grow more from less, need better water-use efficiency and with better roots we might be able to apply less fertiliser,” says Syngenta’s Christian Schlatter.

But soil-borne pathogens, insects, nematodes and abiotic stresses such as temperature and water availability threaten productivity, he says.

“Root health offers new potential for innovation with agriculture – the healthier the roots, the higher the crop productivity.”

But studying roots is complex and requires a multidisciplinary approach. And that’s why Syngenta has set up a Root Health Forum, which brings together global technical experts to exchange knowledge about the latest findings in root health, including new techniques for studying roots and interactions between pathogens and soil.

“It takes one hour to dig out one single root system for a plant and clean it up to analyse it,” he explains. That’s why new sophisticated techniques are proving invaluable in accelerating knowledge.

Researchers at the University of Nottingham are doing exactly that, using a powerful tool to study the structure of roots in their natural environment. This is enabling a greater understanding of them and the effects of important soil-borne pathogens.

The Nanotom is a small-scale computed tomography (CT) scanner that produces high-resolution three-dimensional images of roots and the soil. This enables visualisation of fine details related to different root architectural traits and even root hairs, explains cereal pathologist Rumiana Ray.

It is based on the same technology as is used in medical imaging in hospitals for detecting and treating medical conditions, such as cancer.

This sophisticated scanning is combined with RooTrak, special software developed at the university, which provides quantification of the root architecture traits of a plant. And this technique is helping Dr Ray study the effects of the interaction between rhizoctonia solani AG 2-1 and the root system architecture of wheat and oilseed rape.

Rhizoctonia species are important pathogens in numerous field crops, causing damping off and root and stem rot, yet have not been widely studied, she says.

“AG 2-1 is often overlooked because it is generally considered weakly to moderately pathogenic to wheat.”

Yet survey data has shown that 69% of wheat fields in the UK have the pathogen in the soil, and recent work has shown quantifiable damage to root system development in both wheat and oilseed rape.

Symptoms in wheat are inconspicuous on the roots. The pathogen digests the root cortex, which becomes weakened, so when plants are pulled up and assessed in the field, the infected roots may be lost in the soil. Thus, destructive sampling may fail to reveal the symptoms and impact of the pathogen. And that’s where the non-destructive CT scanning comes into use, by allowing the monitoring of plant roots in soil columns to see the effects of the pathogen over time.

Greater losses are observed in oilseed rape, with the pathogen capable of causing complete inhibition of germination and seedling death. In wheat the pathogen causes a reduction in the number, surface area and volume of the roots, Dr Ray explains.

Building up trouble

“Oilseed rape selects for AG 2-1, so an increase in the rotational frequency of oilseed rape results in greater accumulation of it in the soil.”

“Growers may not be aware of these impacts yet, as this is only just starting to emerge, but highly virulent isolates of this pathogen are capable of causing economic losses for the future unless we have methods for controlling the disease.”

Estimated losses in oilseed rape in Canada range from 30% to 100%, depending upon the AG group that is causing the disease, says Dr Ray.

Wheat losses due to AG 2-1 have not been quantified, but inoculation trials have shown around 10-20% reduction in emergence causing significant reductions in final plant numbers which, in turn, will affect yield, she adds.

Few control options are available for the disease, with few seed treatment products registered for rhizoctonia solani. However, a new molecule from Syngenta, Sedaxane, is proving to be very effective.

The active reduces the symptoms of root rot throughout the growing season, significantly increasing germination and final plant numbers by around 50% when controlling AG 2-1, Dr Ray concludes.

Control

Sedaxane is a new SDHI developed specifically as a seed treatment and, according to Dr Schlatter, is a real innovation in terms of root health.

Commercialised globally under the trademark Vibrance, it is currently registered in all regions of the world on cereals but will have to go through the approval process before becoming available in the UK. In addition, it has registration on soybean, oilseed rape, corn, potato, cotton and rice.

“Rhizoctonia is a very important global pathogen for cereals, oilseed rape, sugar beet and potatoes. In France we are seeing 2-3% yield increases in cereals and up to 5% in Canada. Work on oilseed rape is ongoing, yet the effects in this crop are expected to be even greater.”

Yet the seed treatment’s properties are not just confined to its fungicidal effects. While trials were being carried out it was observed that the compound had additional bio-stimulating properties, which are being investigated by plant pathologist Jean-Marc Seng.

His team at BIOtransfer in France conducted a test tube study of two wheat varieties treated with the fungicide. Sixty days after sowing, one variety showed an 80% increase of the root system, the other variety 40%.

“There is always an advantage to having an improved root system. The plant will have more capacity for adaptation against soil pathogens and will be able to tolerate some loss of the root system.”

Improved rooting also helps the plant tolerate environmental stresses and results in better nutrient utilisation, adds Dr Schlatter.

This increased root biomass is due to secondary (lateral) root proliferation, yet how the fungicide achieves this is yet to be confirmed, says Dr Seng. Studies are now concentrating on using the simplified system in the model plant, arabidopsis (rockcress), to help understand the mechanism.

A similar pot study has mimicked the earlier results, although the root biomass increases were around 50% less than the test-tube study due to soil buffering.

New technique helps boost productivity

Scientists in the USA have developed a technique for studying roots that has proved useful in selecting plants for better rooting and comparing the effects of many agricultural pesticides on rooting.

The approach is based on soft tissue X-ray analysis using low energy X-rays that image the plant root systems, giving high-contrast three-dimensional structures, explains Dan McDonald, the co-founder of Phenotype Screening Corporation.

“Since the penetrating power of soft-tissue X-rays is low, they cannot be used to penetrate through soil. Therefore soft-tissue X-ray imaging is used to image washed root systems or to image root systems grown in special X-ray transparent substrate material,” he says.

And since the imaging is non-destructive and penetrates the entire root volume, pictures of the developing root system can be taken over time. The company has also developed software that automatically scans the X-ray image of the root system and extracts key root traits, he explains.

“Knowing the number and depth of coarse roots, for instance, is an indicator for lodging resistance in maize. The number, density and depth of very fine roots are indicators for nutrient and water exploitation potential.”

The system can allow visualisation of the effects of fungal, insect or nematode infection although not the pests or pathogens themselves, although corn rootworm larvae, nematode egg masses, root galling and root nodules have been captured in the X-ray images.”

“There is a lot to be learned, we are making new insights every day and we are able to get an insight into roots at a faster pace than before,” says Dr McDonald.

Soft-tissue X ray analysis is being used on many globally important crops to help improve productivity.

“It is possible to combine germplasm with stacked traits and with seed treatments to develop root systems that grow faster, grow more deeply, have higher fine root densities, better tolerate stress in the field and contribute to higher yield.”

The technique has uncovered some interesting findings relating to nematode feeding preferences that could help in developing new nematode management options in cotton. Differences in susceptibility of maize plants to corn root worm have also been observed, furthering knowledge into the feeding behaviour of the pest, he concludes.

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