Click on any
image for a more
detailed view

Historical Significance

The late blight epidemics of the 1840s triggered the Irish potato famine, but the history of the potato as a food crop is much older. The potato (Solanum tuberosum) originated in the highlands of the Andes in the Lake Titicaca area between Bolivia and Peru, where native people had selected hundreds of different cultivars (Figure 31) for centuries. Most scientists agree that P. infestans originated in Mexico where both mating types of the fungus are commonplace. Where and how the plant and the pathogen first came together is not certain, but late blight epidemics seem to be described in the northeastern U.S. in about 1843 and Europe in 1845. Potato crops failed for a number of years during the cool and rainy "hungry '40s."

Figure 31

Figure 32

Although poor people who were dependent on potatoes for food suffered in many areas, the disaster was greatest in Ireland (Figure 32). One and one-half million people starved and a similar number emigrated during the famine, resulting in a large Irish diaspora in many parts of North America. As with many famines, politics enhanced the suffering. Many Irish peasants grew cereal crops to pay their rent. Although the grain was harvested, it could not be eaten, and was exported to the English landlords throughout the famine. In the 1990s, many exhibits and gatherings in North America and Ireland commemorated the 150th anniversary of the famine.

Figure 33

One reason that the early history of late blight is unclear is that the germ theory of disease had not yet been accepted. Many preliminary studies of various plant diseases had been conducted, but Anton deBary's (Figure 33) (the "father of plant pathology") conclusive studies finally convinced the scientific community that the white sporulation of P. infestans on infected plants was the causal agent of the disease and not the result of spontaneous generation from the decaying vegetation. Thus, late blight signifies the official beginning of the science of plant pathology. These early studies also contributed to Louis Pasteur's germ theory which was proposed 15 years later.

RETURN TO TOP