Pathogens discovered to be highly adaptable

A study from the U.K. found that crop pathogens can evolve to attack new host plants, which can increase the threat level

As climate change effects become more widespread, plant species are under constant stress to adjust to changing conditions. But many pathogens are ahead of the game. They have shown an ability to adapt, adopt new temperature preferences, and capitalize on host plant diversity and plant ranges at the expense of crop production.

In a study targeting crop pathogens, researchers at the University of Exeter in the United Kingdom profiled hundreds of fungi and oomycetes (also known as water moulds) to assess their adaptability.

“We are interested in understanding how different species of pathogens respond to temperature to help us predict what crops they might affect in the future. For this reason, we decided to gather data on many different fungi that attack plants,” said Dan Bebber, associate professor of ecology in the department of biosciences.

He said that international trade and travel are spreading undesired species around the globe.

“We are seeing growing numbers of crop diseases around the world and many of these have been helped along by climate change,” said Bebber. “Farmers are fighting more and more pests and diseases but need to do so in environmentally friendly ways.”

To understand the diverse abilities of pathogens, scientists used recently developed statistical methods to break down the co-evolution between host plants and parasites. They showed that pathogens can evolve to attack new host plants and, as a result, can increase a threat level.

Traditionally, the researchers wrote in the report, scientists have labelled pests as generalists or specialists. Generalists are often called Jack of all trades, master of none, but Bebber said that many plant pathogens are Jack of some trades, master of others.

“The problem with the term ‘Jack of all trades, master of none’ is that it assumes plant pathogens (or species generally) neatly fit into one of these two categories,” said Tom Chaloner, PhD student working with Bebber. “However, it appears that plant pathogens may be generalists in some regards, and specialists in others.”

Chaloner said in the news release that they collated the largest dataset on plant pathogen temperature responses and made it available to the scientific community. The value of the data is that it allows scientists to test fundamental questions in ecology and evolution. They found that temperatures were narrower when pathogens grow inside plants, illustrating the difference between a fundamental niche and a realized niche.

Ecological niches are defined as conditions or resources needed by organisms in a volume of multidimensional space.

“The niche describes the various environmental conditions that a species requires to survive and reproduce,” said Chaloner. “Each of these conditions has its own shape, or geometry. For example, one species may have a broad temperature tolerance, whereas another species may have a very narrow temperature tolerance. This means the geometry of the temperature niche differs between these two species.

“Niche geometry is fundamental to explaining and understanding why we find species where we do, and so is key to mitigating future destruction caused by plant pathogens.

“The fundamental niche describes all the environmental conditions that enable a species to survive and reproduce and defines where a species could theoretically exist in space and time. In contrast, the realized niche describes where a species is actually found and is a subset of the fundamental niche. These niches differ because of factors such as competition between species. Although central to the science of ecology, empirical evidence for this distinction is rare.”

The challenges presented by highly adaptable pathogens are that farmers and scientists collectively do not always know when, where, or how pathogens will strike next and what impact they will have.

“We don’t know exactly where and when they will strike, but we can make a good guess using available data,” said Bebber. “These educated guesses are called pest risk assessments, or PRAs. Last year we published a large PRA exercise for hundreds of pests and pathogens, making predictions of their next moves based on their current distributions and which crops they attack.

“New pests and diseases arrive (in the U.K.) every year. Sometimes these are spotted early and can be eradicated; sometimes they establish themselves.”

Chaloner said they are researching how destruction of agricultural and natural landscapes caused by plant pathogens may shift under climate change and what, if any, general patterns may occur.

“As the world warms, pathogens which threaten crop production somewhere today may differ to those in the future,” said Chaloner. “In response, farmers will likely need to deploy different or novel control strategies to safeguard crop health. However, predicting how pest and pathogen ranges may shift in the future is multifaceted and very complex.”

The study was published in Nature Communications.

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