Tuesday, August 20, 2019

Driving out potato blight with dual control

October 31, 2017 by  
Filed under Crops

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

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-19th century, 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, they are second only to wheat in national economic importance. The pathogen’s increased virulence in 2011 prompted funding for the latest research, which is reported 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.

Thwarting resistance

“Pathogens such as blight evolve virulence, thwarting the resistance genes bred into the potato,” says Mr 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,” says Mr Carolan. “They may use cultivars with one or more resistance genes but still apply fungicides for peace of mind.

“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.”

Mr Carolan 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.”

Pathogen control

Many growers apply a dose to control the pathogen for only that season. The finding will help agronomists and advisory boards to develop a toolkit for designing the best dose to apply to given varieties, such as Cara or King Edward, that will control and slow the pathogen’s development.

The hope is that containing the pathogen will help reduce its spread for generations to come. Mr Carolan stresses that the finding is 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 Mr Carolan, the same principle could be applied to many other 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, he says.

Beating disease

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.