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United States Department of Agriculture

Agricultural Research Service

Attack of the Witches'-Broom!

Cacao trees damaged by witches'-broomForget Y2K, What about the chocolate shortage in 2003? Money doesn't grow on trees, the saying goes, but chocolate sure does. Or, at least the cocoa bean it comes from. That's why cacao (kuh-COW) tree farmers and chocolate makers like M&M Mars, Inc., are practically biting their nails with fright!



Bad-guy fungi destroy the bean in the cacao podThey're worried that chocolate candy, cookies, cakes and other sweets will be in short supply or, more likely, cost more in the new millennium. Their worry comes from three types of bad fungi that are attacking much of the world's cocoa tree crop. Through 1999, fungus attacks have cost farmers about 3 million tons of cocoa beans already. The fungi must be stopped, experts say. Otherwise, there could be a world chocolate shortage by the year 2003. That's only three years away!

A mushroom named Crinipellis perniciosa growing on dry witches'-broomBefore you go rushing to the grocery store to stock up on your favorite chocolate bars, candies, cookies, or syrup, hold on for a second. There's some good news!

Scientists from M&M Mars, the Agricultural Research Service (ARS) and elsewhere are testing secret weapons. And oddly enough, their weapons are other fungi.

But these fungi, called Trichoderma (trick-oh-DER-muh), don't attack cacao trees. Instead, they protect them--by latching onto the bad fungi and eating their insides.

The battle begins when scientists spray the good-guy fungi onto cocoa trees infected by the bad fungi, called black pod rot, frosty pod rot and witches'- broom. Each fungus causes diseases that rot special pods the cacao tree uses to grow its beans. Then they're no good to eat. The worst damage has happened in South America, Africa and Asia. Each is a favorite home of the cacao tree, a tropical species called Theobroma cacao (thee-oh-BRO-ma).

Cacao beans drying on a cacao farm in BrazilFive to six million farmers on these three continents now make their living growing cacao trees. They're the ones helping satisfy the world's sweet-tooth for chocolate. Americans, for example, eat about 12 pounds of chocolate per person each year. A shortage could be not only a chocolate lover's nightmare--but also a real hardship for the folks who make their living from it.

Today's chocolate lovers are carrying on a centuries old-tradition begun by the ancient Aztecs in Mexico. They called cocoa beans the "food of the gods" and used them as money and gifts and for religious ceremonies. The Aztecs also roasted and ground the beans and mixed them with water and corn to make a bitter drink they called chocolatl, which is where we get the word chocolate. They believed drinking chocolatl was essential to their diet.

Today, the beans are usually picked, ground and mixed with milk and sugar to make chocolate. Peanuts and other foods are often part of the yummy chocolate package.

Dr. Robert Lumsden counts fruiting bodies on witches' broomARS scientists like Robert Lumsden and Prakash Hebbar are working hard to find natural ways of protecting cacao crops from the bean rot fungi. "Spraying the trees with chemicals to control the bad fungi doesn't work very well and costs a lot," says Dr. Lumsden. He's a plant pathologist (path-ALL-oh-jist) at ARS' Biocontrol of Plant Diseases Laboratory in Beltsville, Maryland.

There are also few cacao trees that resist the attack of the fungus, Lumsden adds. His co-worker, Dr. Hebbar, is a microbiologist who works at M&M Mars in Hackettsown, New Jersey. They and South American scientists are testing the helpful Trichoderma fungi as an option to spraying chemicals. And so far, their plan seems to work. In Peru, for example, they are spraying the good fungi onto cacao trees infected by frosty pod fungi. That's Peru's main cacao disease.

Scientists examine healthy cacao podsWitches'-broom growing on cacao treeIn Brazil, scientists are spraying Trichoderma fungi to sweep away witches'-broom, the main cacao disease there. One type of Trichoderma fungus cut the disease by one-third on some infected trees. Lumsden and Hebbar say the battle is far from over. It's also a team effort that includes ARS, M&M Mars, the American Cocoa Research Institute and about 10 international research groups.

You can read more about their rescue effort in the November 1999 issue of ARS'Agricultural Research magazine. Click here to see the story.

--By Hank Becker, Agricultural Research Service, Information Staff
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Last Modified: 2/14/2011
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