Potato blight (or potato late blight) is caused by a mildewlike fungus called Phytophthora infestans that can infect the potato foliage and its tubers. Although P. infestans is best known as a pathogen of the potato, this fungus also attacks the tomato and a number of other plants belonging to the family Solanaceae .
This disease first came to the attention of the world in the 1840s, when it suddenly appeared in Europe and caused the disastrous Irish potato famine. From Europe, the fungus spread all over the world. At first it was thought that the blight was simply due to rainy, cool weather, which caused the potato foliage to turn black and die. In 1863, a German scientist, Anton de Bary, proved that P. infestans was the cause of the disease, and through his pioneering work, deBary established the base for a new science: plant pathology.
In 1884 in France, a fungicide spray containing copper sulphate and lime, called Bordeaux mixture, was discovered to be an effective means of controlling potato blight when applied to the foliage. This was the first time a plant disease was controlled by protective spraying. During the past fifty years hundreds of chemical fungicides have been developed for the control of potato blight. In the early twenty-first century, the potato crop receives more chemicals annually than any other food plant that we grow. The annual losses due to potato late blight, including both the direct losses in yield and the expense of chemical control, amount to billions of dollars a year.
P. infestans passes the winter in infected seed tubers kept in potato storages or in the soil of the potato field to be planted. As the new potato crop becomes established during a cool, wet season, the fungus emerges, sporulates , and attacks both the foliage and the tubers. If this favorable weather continues, the potato plants can be completely destroyed.
Unfortunately, almost all commercial potato varieties are susceptible to blight and must be protected by spraying with chemical fungicides. Although the potato has emerged as one of the four major food crops in the world during the last few centuries (rice, wheat, and corn being the others), the need for expensive protective spraying has tended to confine its major impact to the more prosperous, industrialized countries of the world. It is urgent that we initiate and support a long-term program to enable the potato to continue and expand its contribution to the nutrition of a growing world population.
An obvious solution for this disease problem, which has caused so much expense and uncertainty in world potato production, is to incorporate a durable late blight resistance in commercially acceptable potato varieties. A high level of this blight resistance has been found in a number of wild potato species in Mexico, which is now recognized as the place of origin of P. infestans. These resistant wild potatoes have evolved there, surviving for thousands of years, in a climate favorable for an annual battle with the blight fungus.
Research programs in many countries are now trying to develop commercially acceptable potato varieties with this durable resistance. These resistant potato varieties will not only save the farmer the cost of applying the expensive fungicides, but will provide them with greater security in the production of a good crop of potatoes. Perhaps even more important, for the first time the potato would be available as a basic food crop to many millions of subsistence farmers in developing countries. Today these farmers cannot grow the potato because they do not have the resources needed for the purchase of expensive chemicals used for the control of potato blight.
Today there is an increasing global concern over the quality of the environment. A substantial reduction in the use of agricultural chemicals is considered to be an important step if we are to make progress in improving the environment. The worldwide use of blight-resistant potato varieties would be an important contribution to this program.
see also Breeding; Economic Importance of Plants; Genetic Engineering; Interactions, Plant-Fungal; Pathogens; Potato.
John S. Niederhauser