In the mid-1800s, the Irish potato famine was caused by an outbreak of the late blight potato disease. The failure of the potato crop led to the starvation of an estimated one million of St. Patrick's people, most of them from poor farming families.

Late blight still threatens the world's vital potato crops. Phytophthora infestans, the fungus-like oomycete, or microbe, that causes late blight, can be controlled, but the disease is quickly becoming resistant to efforts to eradicate it with fungicides. Late blight withers plants' leaves and stems and reduces the potatoes to shriveled wastes.

“Late blight threatens potato crops world wide because it is both spectacularly devastating and rapid,” said William Fry, plant pathologist at Cornell University. “The dramatic effects of a late blight outbreak draw attention.”

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Today, the average person on Earth eats 31.3 kilograms (70 pounds) of potatoes per year and farmers in more than 100 nations grow potatoes, according to the United Nations Food and Agriculture Organization.

Potatoes are rich in energy from carbohydrates and supply many vitamins. The potato can grow in poor soils that wouldn't be much use to farmers for other crops. In addition to direct consumption, potatoes are also an important animal feed.

Similar to the Irish famine, present-day economic inequalities compound the threat posed by the potato disease itself. Sharing new techniques for fighting late blight with poor farmers, as well as better international systems for fighting starvation, may be able to ensure that late blight never causes another potato famine.

However, climate change could cause different diseases to replace late blight as the scourge of the potato farmer.

Frying the Disease with Its Own Genes

A few genetically similar varieties of spuds provide the majority of french fries, mashed potatoes and chips on the American table. Those few varieties grow in vast fields of only one crop, or monocultures. The genetic uniformity of the large monocultures -- essentially a shallow gene pool, makes them an open target for epidemics of late blight to start and spread quickly, according to Charles Niblett, president of Venganza, a plant biotechnology company in North Carolina.

“Small epidemics of late blight wipe out production of individual farmers and sometimes whole counties in the U.S. nearly every year,” Niblett told Discovery News. “So yes, a widespread epidemic could wipe out production of a whole state or most of the U.S. potato crop, although that is highly unlikely.”

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Currently, farmers safeguard against disastrous epidemics by using fungicides, planting potatoes at different times in different regions, using disease-free seed and remaining vigilant to outbreaks in order to stop them quickly.

“However, the number of effective fungicides available is declining because some unsafe ones are being removed from the market and the genetically nimble fungus develops resistance to others,” Niblett said.

Niblett's company genetically engineers potatoes to make them resistant to late blight. Their technology inserts modified bits of the late blight's own genes into the potato.

The technique, known as gene silencing, results in potatoes that produce certain strands of genetic material, or RNA, that are similar to those of the late blight disease. When the disease attacks the transgenic potatoes, the modified RNA enters the cells of the fungus-like microorganism and causes it to self-destruct.

“Venganza, our company’s name, means revenge in Spanish,” Niblett said. “We say that the plant is getting revenge on the fungus using the fungus’ own genes.”

Vulnerable Areas to Keep a Potato Eye On

When transgenic late-blight-resistant potatoes become widely available, organizations such as the U.S. Agency for International Development (USAID) and the International Potato Center may help distribute them to the world's poor since it is those groups’ mission to get larger quantities of higher quality and less expensive food into developing countries, said Niblett.

Those new varieties may be most necessary in the regions identified by Greg Forbes, plant pathologist with the International Potato Center. To identify areas most threatened by late blight, Forbes and his colleague Charlotte Lizarraga overlaid the risk of the disease with dependence on potato crops and poverty levels.

“Some areas that stand out are the Andes and the highlands of central Africa, including Ethiopia, as well as the Himalayas, including southwest China and Nepal,” said Forbes. “Basically it is the tropical and subtropical highlands.”

Cross-section of a late blight afflicted potato.Howard F. Schwartz, Colorado State University, Wikimedia Commons

Poverty and the Potato

The Irish famine of the 19th century resulted from a similar combination of poverty, dependence on the potato and the threat of late blight.

“Ireland was a large-scale food exporter before the famine and continued to export food during the famine,” said Kevin O’Neill, Irish studies historian at Boston College.

The problem was the Irish poor could not afford those foods, such as beef and high-quality grain, noted O’Neill. The poor could afford only potatoes, which grow on low-quality land. When the potato crop failed, they had no money for other food.

“The Irish nationalist John Mitchel claimed that the famine was an intentional act of mass murder,” said O’Neill. “Others, of course, disagree. What we can say with confidence is that U.K. government response to the potato failure made a very bad situation much worse and that anti-Irish attitudes played a role in that response.”

In the modern world, organizations like the United Nations can step in to avert famines, said O’Neill. Improved transportation systems and information about crop disasters also reduce the likelihood of another potato famine.

On the other hand, the recent histories of North Korea, Somalia and Sudan show that even if the world is willing to give food, the combination of poverty and repressive governments can block those efforts.

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Climate Change Cooking Up New Potato Problems

Regardless of any government, nature is the ultimate ruler of the potato harvest. Changing weather patterns could result in the rise of a different potato plague.

Jacquie van der Waals, plant pathologist at the University of Pretoria, suggested the threat of late blight might drop in regions that are becoming warmer and drier, since the disease thrives in cool, damp conditions.

However, climate change may benefit another disease, according to van der Waals.

“The leaf disease that is most likely to be intensified by climate change is early blight, caused by Alternaria alternata,” said van der Waals. “This disease is most severe in warm conditions, particularly in alternating wet and dry spells, which is exactly what we are expecting to encounter with climate change.”

South Africa has already seen a substantial increase in the incidence and severity of early blight over the past decade, according to van der Waals. Other researchers have observed an increase in the disease in the Andes. Both Africa and the Andes are regions Forbes identified as at-risk for potato disasters.