V. THE IMPACT OF FUNGI ON HUMAN POPULATIONS

In the previous sections we have discussed the beneficial and detrimental activities of fungi. how they have been used in various religious ceremonies dating back 4-5,000 years, how chestnut trees have been essentially eliminated and how the American elms are on their way out, how ergotism wreaked havoc on European communities, and how reduced immune responses in humans have made man more susceptible to fungi. While the discovery and practical use of penicillin was perhaps instrumental in saving thousands of lives during WW2, and how the use of species of Saccharomyces in the making of bread, wine, and cheese has made it the most economically important fungus, no single fungus has had as great an impact on human populations as Phytophthora infestans, the cause of late blight of potato (Am. Phytopath. Soc., News Release, Sept. 15, 1994).

In the early 1800’s, over a million Irish died and almost 2 million fled from the ravages of late blight on potatoes. Potatoes were first grown throughout the western areas of South America and in Central America, dating back to 400BC. European explorers brought potatoes along with many other new world plants to Europe in the mid 16th century. The potato slowly gained popularity in Europe. Soil, climate, and other factors made potato farming easy in Europe and potato farming spread into Ireland by the 17th century. By the early 1800’s the Irish were almost completely dependent on the potato for food. Settlers from England and Ireland brought the potato with them whenever they settled in North America. In 1842, the first report of late blight of potato in the U.S. was reported near Philadelphia, PA.  Within a few years the blight hit Europe.  Whether the fungus was brought into Europe from diseased plants or tubers from the US, or from plants that had been brought years earlier from South America, is debatable. The cool, moist climate of early summers in Ireland was ideal for the outbreak of potato blight in their fields. It was during the decade of the 1840’s that late blight wiped out the potato crops annually in Ireland. It was during this period that the massive deaths and immigration cited above occurred. In 1863,  Anton DeBary established that a fungus was the caused of late blight, and he called the fungus Phytophthora infestans, which means devastating plant destroyer. After the discovery of the cause of late blight, management practices, chemical, and other control procedures have been used effectively. But the fungus survives so well on old tubers in the soil that eradication is impossible. For many years it was believed that only one mating type of the fungus existed in North America. In recent years, however, both mating types have been found and it is believed that this is responsible for the occurrence of resistant strains of the fungus that has been found in several states of the Pacific Northwest, British Columbia, and in several other states, including Florida. Research is actively underway to attempt to come up with resistant strains of the potato. With modern day technology, new germplasm may be found or induced and introduced into current strains of potatoes.

While the potato is an important food product around the world, there appears to be no society that is totally dependent on one source of food as did the Irish. The problems with chestnut blight, Dutch elm disease, and other current epidemics tell us that fungi can get an advantage and essentially destroy a species. In human pathology, the number of fungal diseases is small in comparison to bacteria and viruses. However, we are now learning that with a compromised immune system, a large number of fungi that were a minor problem can be devastating to an AIDS patient.  Perhaps with the new arsenals of molecular techniques, we can stay ahead of the fungi that damage us and our food, clothing, and shelter; while enjoying the rich benefits of fungi that help us to sustain the quality of life we now enjoy.