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Resistance Genes Key to Protecting Chocolate Supply

By Don Comis
October 15, 2001

Anyone who needs a chocolate fix would do well to fear witches’ broom, frosty pod rot and black pod.

A major supplier of chocolate lovers, Mars, Inc., wants to protect the world’s cocoa beans from these and other fungal diseases. Agricultural Research Service scientists, led by plant geneticist Raymond J. Schnell at the ARS Subtropical Horticulture Research Station in Miami, Fla., have signed a research agreement with Mars to develop more resistant cacao trees as quickly as possible.

Large pods holding 20 to 60 cocoa beans rich with chocolate butter sprout from cacao trees. The diseases rot mature pods. Witches’ broom gets its name from the white, broomlike fungal structures that form on leaves, pods and stems. It also inhibits new pod formation.

Witches’ broom has reduced Brazil from a net exporter to an importer of cocoa beans. Frosty pod rot has closed farms in Ecuador, Colombia and Costa Rica. Now, black pod rot threatens the West African plantations that supply more than half of the world’s cacao. If the other two diseases were to reach West Africa and join forces with black pod, the world could all but kiss chocolate goodbye.

ARS scientists have found 75 cacao genes similar to resistance genes in other plant species. These may help scientists breed more resistant varieties. If the resistance genes are clustered together, the known genes could lead to discovery of their neighbors.

The United States is working with Brazil, Costa Rica, Trinidad, Ecuador and the United Kingdom. These countries have long-standing cacao breeding programs and have supplied the range of plants needed to map the cacao genome’s 10 chromosomes.

Mars, Inc., has waived its patent rights to any new varieties that might result from this research.

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