Crop scientists have confirmed another tool for the armoury to control plant diseases whose pathogens can mirror the evolution of antibiotic resistant bacteria in humans.

  • 20
  • SEP
  • 2017

Combining methods of disease control rather than relying on a single resistance strategy can extend the durability of crops by many years, confirms computer modelling that draws on classical population genetics theory.

The finding comes from assessing the spread and virulence of the pathogen responsible for late blight of potato, Phytophthora infestans. The pathogen, which caused the Great Irish Famine in the mid-nineteenth century and led to the new science of plant pathology, evolved into a serious threat again in the UK in 2011.

Potatoes are world’s fourth major crop after wheat, rice and corn. In the UK, potatoes are second only to wheat in national economic importance, and emergence of the pathogen’s increased virulence in 2011 prompted funding for the latest research, which is reported today in Proceedings of the Royal Society B.

Fungicides and resistant cultivars were the chosen disease control methods, as these are most commonly and easily applied, says Kevin Carolan, a pathogen evolution modeller at Rothamsted Research, which led the project with Fera Science, Scotland’s Rural College and ADAS.

“Pathogens such as blight evolve virulence, thwarting the resistance genes bred into the potato,” says Carolan. “We have shown that appropriate use of fungicides can slow this evolution, so the resistance genes are more durable, preventing loss of disease control.”

“Some farmers already use more than one method to contain disease within their crops; they may use cultivars with one or more resistance genes but still apply fungicides for peace of mind,” notes Carolan. “Our research provides evidence for such an approach, and for similar approaches using a combination of other methods, and indicates how the timing and degree of dosing, for instance, will affect resistance to disease.”

He adds: “We’ve shown that certain doses of fungicide will accelerate the evolution of virulence in the pathogen, making the problem worse, and other doses will slow the evolution of the pathogen protecting genetic resistance in the cultivars.”

Pictured: Blight turns potato black and rotting, scorching the crop’s leaves similarly

Many growers apply a dose to control the pathogen for only that season, says Carolan: “Our finding will help agronomists and advisory boards to develop a toolkit for designing the best dose to apply to a given cultivar, such as Cara or King Edward, that will not only provide immediate containment of the pathogen but also slow its evolution, so controlling the disease for generations to come.”

Carolan stresses that the finding represents a general technique to maintain the effectiveness of cultivar resistance. Combining other methods of disease control could also reduce the growth rate of epidemics; methods such as biological control organisms, changes to soil fertilisation levels or agronomic measures, including planting date, planting density and intercropping.

Futhermore, says Carolan, “we chose a model of the evolution of P. infestans but the principle could be applied to many different crops and pathogens. In fact, in principle, it would be applicable to the evolution of drug resistance in the medical fields.”

The researchers see their finding as an additional general method to delay the evolution of virulence, which supplements three widely advocated techniques and is easier for growers to apply. Current techniques include using mixtures of resistant cultivars, deploying genetic resistance differentially in time and location, and designing cultivars with multiple resistance genes; all these methods involve practical disadvantages.

The paper’s core thesis derives from classical population genetics theory: “selection for virulence can be slowed by introducing additional disease control methods, slowing the growth rate of the entire pathogen population.”

Funding for the work came from the Biotechnology & Biological Sciences Research Council, with additional support from Syngenta, BASF and Belchim, which was co-ordinated by the Agriculture & Horticulture Development Board.

About Fera Science

Fera is a national and international centre of excellence for interdisciplinary investigation and problem solving across plant and bee health, crop protection, sustainable agriculture, food and feed quality and chemical safety in the environment.

We create and deliver integrated, innovative and expert research services and products for our partners in crop protection, chemical and animal health companies, as well as food producers and growers, manufacturers, distributors and retailers. We also support and work closely with governments, academia and leading research organisations.

About Scotland’s Rural College

Four respected partners – Barony, Elmwood and Oatridge Colleges and the Scottish Agricultural College – merged in 2012 to become Scotland’s Rural College, SRUC. We exist to deliver comprehensive skills, education and business support for Scotland’s land-based industries, founded on world class and sector-leading research, education and consultancy. The integration of these three complementary “knowledge exchange” services is of significant value to all with an interest in land-based activities – be they learners, businesses, communities or policy-makers.

About ADAS

ADAS is the UK’s largest independent provider of agricultural and environmental consultancy, rural development services and policy advice. ADAS has a unique combination of insight and practical experience, underpinned by robust, informed, science-based information that allows us to meet the needs of both our domestic and international clients. Our great strength is our breadth and depth of expertise spanning the entire environmental sector.

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; Twitter @Rothamsted
1Rothamsted Research and the Value of Excellence: A synthesis of the available evidence, by Séan Rickard (Oct 2015)

The Biotechnology and Biological Sciences Research Council is part of UK Research and Innovation, a non-departmental public body funded by a grant-in-aid from the UK government.
BBSRC invests in world-class bioscience research and training on behalf of the UK public. Our aim is to further scientific knowledge, to promote economic growth, wealth and job creation and to improve quality of life in the UK and beyond.
Funded by government, BBSRC invested £469 million in world-class bioscience in 2016-17. We support research and training in universities and strategically funded institutes. BBSRC research and the people we fund are helping society to meet major challenges, including food security, green energy and healthier, longer lives. Our investments underpin important UK economic sectors, such as farming, food, industrial biotechnology and pharmaceuticals.
More information about BBSRC, our science and our impact.
More information about BBSRC strategically funded institutes

About LAT
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.