The disease

The disease is caused by a re-encounter rust fungus that is indigenous in Central America but exotic to Africa. When maize was taken by the Spanish to Europe, the disease may have been left behind but, in any event, it lacked epidemiological competence in its new area of cultivation. When the Portuguese subsequently took maize from Europe to Africa, it was free of tropical rust, and the maize of Africa remained free for rather more than four centuries. Tropical rust reached West Africa only in the late 1940s, with the development of trans-Atlantic air transport.

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