TAKING ON TAKE-ALL
Science is getting nearer to the root of this costly problem
Considered the most damaging root disease of wheat worldwide, take-all causes significant financial costs by reducing wheat yield and grain quality – with losses estimated at between 5 - 20% annually in the UK, and more than half of the crop lost in years of high disease severity.
Caused by the soil-dwelling fungus Gaeumannomyces tritici, control measures are limited, however, a newly published review summarises advances in take-all research and offers farmers a small glimmer of hope.
According to lead author and head of take-all research at Rothamsted, Dr Javier Palma-Guerrero, considerable progress has been made in our understanding of this disease in recent years – not least because additional phases of the annual disease cycle have been formally recognised and investigated by combining crop genetics and soil microbiome analysis.
“New sources of genetic resistance have been identified and these are being investigated and transferred into wheat. And we now have a better understanding of the soil, rhizosphere and endosphere [plant interior] microbiomes, and their association to different wheat cultivars, which shows the importance of considering all these interactions to achieve efficient disease management practices.
“That’s said, there are still many unknowns, especially at the molecular and community population levels. As no resistant or even partially resistant commercial wheat cultivars to take-all are available, and chemical control is still limited, control measures are largely restricted to crop rotation - and new control strategies are urgently needed.
“In addition, climate change is expected to make matters worse as areas where autumns and winters will become milder and wetter will favour fungal diseases of plants.”
First the good news: the ancestral wheat Triticum monococcum has been identified as a potential gold mine of resistance genes to take-all - the bad news is these genes have yet to be identified, and the genetic and mechanistic basis of this species’ resistance is not known.
A few other wheat relatives are also showing promise for their resistance to take-all, as are mechanisms of resistance found in other cereals such as oats and rye, and all of these are currently being investigated.
“We also know that the bacteria present in the soil have an effect on the disease, either enabling or hindering the fungus,” says Dr Palma-Guerrero. “In fact, work at Rothamsted has shown that a greater overall number of Pseudomonas bacteria in the soil is correlated with higher disease pressure. For unknown reasons, when the soil is lean in Pseudomonas bacteria the take-all fungus does not do so well.”
Another promising area for research is the transcriptome – the array of messenger molecules that turn DNA instructions into proteins.
The fungus and wheat transcriptome have both been characterised during the infection process, providing new gene targets for future antifungal development or for improving host resistance.
The available transcriptome data will also allow comparisons with similar disease systems, so as to compare the plant responses between different organs, for example between roots and leaves, and between biological and climate driven stresses.
In addition, by silencing certain fungal genes, researchers have now been able to ascertain the function of specific genes within the fungus and how important they are in the infection process.
According to Dr Palma-Guerrero, such studies have previously proven difficult but advances in genetic techniques have opened the door to these new approaches.
“The developments in genome sequencing techniques and comparative genomics, now make it possible to construct a ‘pangenome’ for this species, which will contain information from all the different global strains and which genes are found in all strains and which are not.
“Plus, the recent advances in genome editing tools, like CRISPR-CAS 9, will promote the understanding of the take-all molecular mechanisms of virulence in the near future, which together with virus/host-induced gene silencing and virus-induced over expression of wheat root genes, will allow precise dissection and elucidation of the key molecular interactions underlying this disease.”
The review paper was published in Trends in Plant Science.
About Rothamsted Research
Rothamsted Research is the longest-running agricultural research institute in the world. We work from gene to field with a proud history of ground-breaking discoveries, from crop treatment to crop protection, from statistical interpretation to soils management. Our founders, in 1843, were the pioneers of modern agriculture, and we are known for our imaginative science and our collaborative influence on fresh thinking and farming practices.
Through independent science and innovation, we make significant contributions to improving agri-food systems in the UK and internationally. In terms of the institute’s economic contribution, the cumulative impact of our work in the UK was calculated to exceed £3000 million a year in 20151. Our strength lies in our systems approach, which combines science and strategic research, interdisciplinary teams and partnerships.
Rothamsted is also home to three unique resources. These National Capabilities are open to researchers from all over the world: The Long-Term Experiments, Rothamsted Insect Survey and the North Wyke Farm Platform.
We are strategically funded by the Biotechnology and Biological Sciences Research Council (BBSRC), with additional support from other national and international funding streams, and from industry. We are also supported by the Lawes Agricultural Trust (LAT).
For more information, visit https://www.rothamsted.ac.uk/; Twitter @Rothamsted
1Rothamsted Research and the Value of Excellence: A synthesis of the available evidence, by Séan Rickard (Oct 2015)
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The Lawes Agricultural Trust, established in 1889 by Sir John Bennet Lawes, supports Rothamsted Research’s national and international agricultural science through the provision of land, facilities and funding. LAT, a charitable trust, owns the estates at Harpenden and Broom's Barn, including many of the buildings used by Rothamsted Research. LAT provides an annual research grant to the Director, accommodation for nearly 200 people, and support for fellowships for young scientists from developing countries. LAT also makes capital grants to help modernise facilities at Rothamsted, or invests in new buildings.