ITHACA, New York (CNN) -- More than 150 years after the Irish potato famine, aggressive relatives of the disastrous fungus are making themselves at home all over the world. But scientists are fighting the blight with efforts to develop new disease-resistant plants.

For generations, potato late-blight fungus has been the enemy of the world's potato farmers. Scientists believe the strain originated in Mexico and traveled in the 1840s to Ireland where it killed nearly all of Ireland's potatoes.

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The resulting famine led to about 1 million deaths. Nearly 2 million more people were forced to emigrate.

The new, stronger strain of potato late-blight fungus may also have come from Mexico. Scientists believe it was exported from there to Europe in the 1970s in potato shipments which then traveled worldwide.

Multibillion-dollar problem

William Fry, a professor of plant pathology at Cornell University, estimates the new strain has caused about $3 billion in annual crop losses and has cut international potato production by 15 percent.

Fry, who has studied the fungus for 25 years, says several things make the new strain more virulent, including a resistance to chemicals that kill fungi. ( 73 KB/7 sec. AIFF or WAV sound)

The International Potato Center, a research organization, has used cross-breeding and molecular biology to create potatoes that are blight-resistant, says Wanda Collins, deputy director. ( 88 KB/8 sec. AIFF or WAV sound)

But being fungus-resistant doesn't mean a potato will have international taste appeal. That's why, explains Collins, several dozen varieties are available. ( 80 KB/7 sec. AIFF or WAV sound)

Scientists hope to have the new late-blight-resistant potato plants in worldwide use within five years.

Reporter Allard Beutel contributed to this report.

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