‘Late blight’ is still the biggest threat to Irish potato crop

The same microbe that caused the Great Famine of 1845 continues to pose a biotic risk today
‘Late blight’ is still the biggest threat to Irish potato crop

More than 175 years ago it was the root cause of Ireland’s Great Famine, a period of mass starvation and a cultural watershed during which more than a million people died and a further million left the country in a crisis which changed the face of this country forever.

Today, Ireland has recovered from the ravages of the terrible years between 1845 and 1852 — yet, scientists warn, that same microbe, Phytophthora Infestans, still continues to pose a serious biotic threat to global potato crops, with intensive fungicide programmes rigorously implemented for its control on an annual basis.

“It is probably a more aggressive, more virulent and more difficult pathogen to control than it was back then,” explains Dr Steven Kildea, senior research officer with Teagasc Crops, Environment and Land Use Programme, and author of a new report on the microbe, recognising the 175th anniversary of its arrival in Ireland.

In fact, while fungal, bacterial, and viral pathogens continue to shape global societies, he says, there are few plant-specific pathogens that can be regarded as having impacted the world throughout the 19th and 20th centuries in the way Phytophthora infestans has.

This is because it has mutated and adapted around the measures we have put in place to control it. 

"As a pathogen it is not native to the majority of the world and when you introduce it, it can basically run amok,” he says.

The battle to control the microbe, also known as late blight, is virtually an ongoing “arms race” — both between the pathogen and the plant, and between the pathogen, the farmer and modern science.

What happens he explains, is that when scientists and farmers put a particular layer of control in place, a strain of this pathogen eventually adapts — and jumps the hurdle.

Potato blight remains the greatest threat to farmers.

Potato blight remains the greatest threat to farmers.

“From an Irish potato producer’s perspective, this is, and continues to be, the number one threat for producers,” explains Dr Kildea.

Modern science, however, he emphasises, manages to stay one step ahead of the blight.

“Looking back 175 years ago, when this pathogen arrived, people did not understand that microbes actually caused disease," he says.

“The assumption was that the plant died for some reason and then the disease came — but it was the microbe that caused the disease.” 

The arrival of late blight in Europe and its resulting devastation, however, also led to the development of the science of plant pathology with the discovery that microbes can cause the infection and are not only a symptom of disease.

"We understand the microbe now. We adapt and put measures in place," Dr Kildea says.

As scientists, we understand what makes this pathogen tick, and we put programmes in place to prevent it.

Another element of this ongoing battle, he says, lies in developing resistant varieties of potato so that the plant itself could prevent the pathogen from taking hold. 

This has to be done in a way that was acceptable to the consumer, he explained, which was where modern breeding programmes came in. 

The third element in the battle against late blight is the environment — although the Irish climate is inevitably conducive to the disease, as Ireland was exposed to westerly winds, lots of moisture and mild weather.

“Knowing this, we target our infection prevention measures, which means farmers target their pesticides based on when the infection is predicted to occur — it is about preventative measures being implemented on the basis of knowledge about the weather.” 

The impact of the potato crop failure during the Famine was devastating. More than a million people died.

The impact of the potato crop failure during the Famine was devastating. More than a million people died.

These three elements are the cornerstones in the battle to control this formidable pathogen, he explained.

In essence, science now attacks every element of the “disease triangle” says Dr Kildea — working on ways to manage the pathogen, control environment and control the host potato crop.

So what is it about this pathogen that makes it such a threat to Irish potato crops? Although late blight caused by  Phytophthora infestans is often referred to as a fungal disease, it is actually an oomycete, more closely related to brown algae than to true fungi.

The differences between oomycetes and fungi may be subtle but can have enormous consequences: for potato growers this is probably most evident in the different chemicals used to control them.

Most fungicides used to control cereal diseases provide no control against late blight and those used for late blight have little or no effect on cereal diseases, he explains in an article in the latest edition of Teagasc’s TResearch Journal.

“Over the past 175 years  Phytophthora infestans has demonstrated that it can also readily adapt to overcome any changes imposed, whether directly or indirectly, in the form of the host or environment.

As production systems in Ireland and throughout Europe have changed, the economic consequences associated with even minor outbreaks of the disease have increased.

“This has led to increased monitoring of the pathogen for changes that may indicate potential changes in disease development and subsequent control measures.

 “There is hope, even though it is as potentially destructive as it was 175 years ago, we now have the knowledge to prevent it from being destructive. 

"We are trying to stay one step ahead. We are making sure that we can control it — but it is a battle.”

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