Some Striking Fungal Diseases 421 Diseases of Crop Plants

4.2.1.1 Late Blight of Potato

We stop the press, with great regret, to announce that potato murrain has unequivocally declared itself in Ireland. The crops around Dublin are suddenly perishing. Where will

Ireland be in the event of a universal potato rot.

Gardner's Chronicle, September 13, 1845

The potato was once the staple crop of Ireland and people depended on this single crop as their primary food source. In the late summer of 1845, the "fungus" (see Appendix) Phytophthora infestans (Straminipila) almost completely devastated the potato crop, resulting in famine. Between 1845 and 1851, almost a million people died of starvation and about a million-and-a-half migrated to America. Because of the economic importance of potato, Phytophthora infestans contributed greatly to investigations on fungi as a whole and to the development of the science of plant pathology.

4.2.1.2 Downy Mildew of Grapes

About thirty years after the Irish famine, Plasmopara viticola (Straminipila) threatened the vine industry in France. This fungus causes the downy mildew of grapes and was well known in America as a mild pest. In 1876 an American mycologist, W.G. Farlow, warned that if the fungus ever reached Europe, it might prove to be disastrous since the climate in Europe was more favorable to the growth of this fungus. His prediction came true: within two years the first diseased vines were found in France and by 1882 the mold had spread through most of the vine-growing districts. By a rare combination of chance and keen observation, Pierre Millardet, a professor of botany at Bordeaux and a former pupil of de Bary, observed that the conidia did not germinate in water from his well. The reason for the non-germination was traced to a small amount of copper that had leached from the brass pump. He also observed that vine leaves sprinkled with lime and copper sulfate to discourage thievery were free from mildew. Spraying experiments proved that covering leaves and buds of the vines with a mixture of copper sulfate and lime protected the crop whereas unsprayed vines developed infection, showed defoliation and produced no crop. This fungicide since known as the Bordeaux mixture has found wide application.

4.2.1.3 Coffee Rust

Until the middle of the nineteenth century, the consumption of tea and coffee in England was nearly equal. In 1870s, the coffee rust caused by Hemileia vastatrix (Basidiomycotina) defoliated leaves and totally ruined the coffee crop in Ceylon (now Sri Lanka). The coffee export to England ceased and the British were forced to change their drinking habit to tea; thus today the British drink more tea than coffee. The coffee rust in Ceylon gave a big boost to tea cultivation by the British settlers in the Indian subcontinent, particularly in the Himalayan mountain ranges and the cultivation of tea in India.

4.2.1.4 Rice Blast

Rice is the staple food for half of the world's population and suffers from a serious threat of the rice blast fungus, Magnaporthe grisea (Ascomycotina). Blast disease is threatening Vietnam's winter-spring rice crops nationwide (http://www.cps-scp.ca/riceblast.htm). The fungus is favored by high relative humidity and temperatures around 25°C. It produces brown lesions on leaves, the chief photosynthetic organs in plants, and can be very injurious to plant tissues. The grains are not filled and the entire panicle may die while the blast fungus survives from one season to the next on diseased rice straw and stubble. The entire genome of the fungus has been sequenced at the Whitehead Institute.

4.2.1.5 Corn Leaf Blight

In 1970, the corn leaf blight fungus, Bipolaris maydis (Helminthosporium maydis) (Fungi Anamorphici) destroyed much of the corn crop in the United States, causing an estimated loss of $1 billion. The disease is favored by moist, warm weather.

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