Every year plant diseases affect human society, resulting in inadequate nutrition and economic loss. The potato famine in the mid- 1800s is the best-known example of a fungal plant pathogens effect on history (2-4); Phytopthora infestans has recently reemerged in the Americas (5). Among the silent problems that have enormous effects on human society each year are crop infections by geminiviruses and tomato spotted wilt virus (6). These plant viruses are transmitted by whiteflies, leafhoppers, or thrips to hundreds of species of plants. They cause diseases of crops and ornamental plants around the world.
More obvious problems include ergotism, caused by the alkaloids produced by the fungus Claviceps purpurea. Ergotism was associated with the growth of rye, particularly in cool climates that cannot support wheat, and was implicated in the aberrant human behavior responsible at least in part for the Salem witch trials and St. Anthonys fire (2,7). In the last 5 years, a new plant disease, sorghum ergot (Claviceps africana), has spread north from Brazil into the United States. This fungus also causes disease in Australia, a sudden change from its known occurrence in Africa (8). Sorghum is the fifth most important cereal crop in the world, with approximately 45 million hectares under cultivation for food, beverages, feed, and fodder (8). Ergot alkaloid toxicity has not yet been demonstrated, but potential nutritional and economic losses could have substantial impact on public health.