The Plant Pathology Laboratory: Explore History, The Potato Famine

Irish Potato Famine (1845)
The Birth of a New Science

Potatoes are not native to Ireland, rather they were brought from South America in the 16th century. By the 19th century Irish peasants were dependent upon the potato for food (hence the name Irish potato), often consuming 8-14 pounds a day. Peasants could grow enough potatoes on smaller plots of land to feed the family, and use the remaining land to grow the grain used to pay the rich English landowners. The Irish population was booming during this time. It grew from 4.5 million in 1800 to more than 8 million in 1845. The huge population was soley dependent on potato for nourishment.

The weather early in the growing season of 1845 was sunny and the crops were doing well. But the weather began to change, it became overcast (which lasted more than six weeks) and the temperatures were recorded to be 1.5-7 degrees below the average. The potato vines in the field became a blighted mass of dying vegetation and tubers were found to be rotted. Those tubers appearing sound rotted away in storage. The cool rainy weather affected all crop yields but the effect was most severe on the potato crop. The white fungus found on the blighted vines was considered to be result rather than a cause of the blight. Dramatic changes began to occur in the Irish population. One million starved to death and 1.5 million emigrated (left) to the United States and Canada. The English landlords had no sympathy for the Irish and evicted them when unable to pay rent.

Finally in 1853, Anton de Bary, a German Botanist, proved the role of a fungus in the blight. He used experiments in which he put potato plants in a cool, wet environment. He added to some plants sporangia from the fungus and to the remaining plants he added nothing (these would be the control plants). Even though all the plants were kept under the same environmental conditions only those with sporangia added became blighted. de Bary's experiments triggered major advances in plant disease research and in human and animal disease research as well.

The fungus had been named Botrytis infestans by Montagne, but de Bary observed that this fungus was not really similar to other fungi of the Botrytis genus. So de Bary created the genus Phytophthora, and named the fungus Phytophthora infestans, (phyto=plant and phthora=destroyer and infestans suggested the devastation of the disease). So was the birth of a new discipline, many other scientist began to report other fungi capable of infecting plants. Many observations were made concerning the potato famine that have impacted Plant Pathology. Disease was no longer viewed as some dark, magical force, but now a biological system involving microorganisms. Also components of what is called the disease triangle are seen in the tragedy of the potato famine. The weather changed drastically that year, it was damp and cool. This environment was perfect for the pathogen. So those two parts of the triangle were present. The host, or the potato crop, was also present. The potato crop was derived from only a small amount of tubers that had arrived from South America. So every potato plant in the field was nearly genetically identical, if one plant was susceptible then all the plants in the field would be susceptible. So all the components were there, the susceptible host, the pathogen and the optimal conditions for the pathogen. So began a disasterous disease and the birth of a new science. To learn more about this fungus check out this web site Plant Disease Lessons-- Late Blight of Potato and Tomato

(Lesion, Fungal growth, and fungal sporangia images courtesy of Mary Powelson and Debra Inglis from their website The On-line Field Guide to Potato Late Blight)

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