The Science of the Famine

Potato Crops Worldwide
are threatened by the same
fungus which caused the
Irish Potato Famine

Weed Implicated in Potato Blight Persistence

Late blight, the devastating tuber disease that triggered the Irish potato famine of the mid-1800s, has a new partner in crime.

Scientists with the Agricultural Research Service (ARS) in Orono, Maine, discovered that Phytophthora infestans—the microorganism behind the spud-spoiling disease—is seeking refuge in potato fields, holed up in an alternate host plant: hairy nightshade.

Best known for causing widespread hunger, illness and death in 1840s Ireland, P. infestans continues to pose a formidable threat to global potato and tomato production. According to the International Potato Center in Lima, Peru, the disease costs the world's growers more than $3 billion each year in fungicides and other control measures.

Modesto Olanya, a plant pathologist at the ARS New England Plant, Soil and Water Research Laboratory in Orono, learned of the possibility of an alternate host in 2004 from colleagues at the University of Maine Cooperative Extension in Presque Isle.

As extension agents in the northern part of the state discovered, hairy nightshade plants were showing up speckled with suspicious dark and oily spots. Olanya analyzed the microorganisms on the plants and verified, for the first time, that hairy nightshade is an alternate host of P. infestans in Maine.

To make matters worse, hairy nightshade is hardly a wallflower, in terms of its presence in commercial potato fields in Maine. In a limited survey, Olanya and University of Maine collaborators found that 55 percent of fields assessed in the state contained the plant.

According to Olanya, the finding that hairy nightshade is an active host of P. infestans is problematic in two ways. First, the plant is a secondary source of the destructive disease. And, it's a weed.

As a result of this ARS research, growers are now learning the importance of controlling hairy nightshade as part of their overall late blight management program.

ARS is the chief scientific research agency of the U.S. Department of Agriculture.

Researcher Identifies Irish Potato Famine Pathogen

ScienceDaily (Mar. 19, 2004) — In June 2001, North Carolina State University plant pathologist Jean Beagle Ristaino shocked the scientific world when she published a paper in the journal Nature that called into question the then-prevailing theories about the strain of pathogen – and its place of origin – that caused the Irish potato famine in the 1840s.

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Using DNA fingerprinting analysis of 150-year-old leaves – evidence that had not previously been studied – Ristaino ruled out the longtime prime suspect behind the famine: the Ib haplotype, or strain, of the late-blight pathogen Phytophthora infestans, which was presumed to have originated in Mexico.

Now, in a new study, Ristaino and postdoctoral student Kim May point the finger at the Ia strain of P. infestans, and trace its probable roots to the Andes Mountains in South America.

The study will be published in the April 2004 edition of Mycological Research.

The researchers used DNA sequences from mitochondrial DNA to examine 186 specimens from six different regions of the world dating from as early as 1845 to as late as 1982. The specimens included ones from late-blight epidemics in Ireland, the United States and continental Europe, and came from collections housed in England, Ireland and the United States.

About 90 percent of the specimens were confirmed to be infected with P. infestans, the paper reports. About 86 percent of the specimens – including those involved in major epidemics in Ireland and other locations around the globe – were infected with the Ia haplotype of P. infestans. The Ib haplotype – the one previously presumed to be the culprit behind the Irish potato famine and other epidemics before Ristaino's groundbreaking 2001 study – was present only in more modern samples from Central and South America.

Moreover, the researchers found two strains – Ia and IIb – in potato specimens studied from 1950s Nicaragua. This finding further debunks the single-strain theory that prevailed before Ristaino's 2001 Nature paper.

Ristaino's lab is currently investigating the center of origin of P. infestans. She hypothesizes that the pathogen originated in South America and perhaps made its way to Europe and the United States via exports of potato seed on steamships. The data to support this hypothesis will be published by one of Ristaino's graduate students, Luis Gomez, in the next year.

There are four haplotypes of P. infestans – Ia, Ib, IIa and IIb – which is a fungus-like pathogen that causes severe lesions on leaves of potato and tomato plants.

The late-blight pathogen led to the Irish potato famine, which killed or displaced millions of Irish people, and other epidemics across the world. Late blight continues to wreak havoc as a major potato and tomato killer, which makes Ristaino's research all the more important.

"If we can understand the strains of P. infestans that are out there now and see how the pathogen has evolved over time – including how it mutates in response to fungicides or host resistance – we'll better be able to manage the disease," Ristaino said.

The research is funded by the National Geographic Society, the USDA National Research Initiatives Cooperative Grants Program, the North Carolina State Agricultural Research Service and NC State's International Programs Office

Science Update page -- A nice narrative of the history of the Famine, with explanations of some of the potato diseases which caused it.

The Science of Potatoes

Experiments to Do

Potato battery

The noise is caused by an electric current. The potato and wires produce an electric current in the same way as a torch battery, but only a very weak one. The sap of the potato reacts with the metals in a chemical process and also produces electrical energy. We speak of a galvanic cell because the Italian doctor Galvani first observed this process in a similar experiment in 1789.

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