March is the month that will forever be associated with the Irish, who are themselves forever associated with our favorite crop: the potato. As a potato pathologist, the Irish and the potato will also be forever linked in my mind with late blight of potato, as this was the disease responsible for the Great Famine in Ireland that began in 1845. By the way, the name of the causal organism of late blight, Phytophthora infestans, literally means “the terrible plant destroyer.”
The story of how the Irish became all but completely dependent upon the potato as their only food source is a fascinating one in its own right and emphatically demonstrates the profoundly negative effect that rigid, outdated and even punitive political attitudes can have on a people and nation. The Great Famine is certainly a tale of tragedy and hardship but there is, believe it or not, a positive side to what is an otherwise very depressing story. It has to do with the dramatic and sweeping revolution within the science of biology that was triggered by a concerted effort to understand this disease.
The occurrence of late blight in Europe and in Ireland during the 1840s came at a time when the causes of diseases in plants and animals, including humans, were still poorly understood. The topic was often the subject of heated debate. As the new late blight disease began to ravage potato crops in Europe, the Rev. M.J. Berkeley, a clergyman in England who had a passion for botany, suggested that the fungus he had frequently observed in association with the disease might actually be the cause. Prior to this time, the micro-organisms often found associated with diseased plants were thought to be present because the plant was diseased and not because they were actually causing the disease.
Berkeley’s seemingly innocent suggestion led to another round of contentious discussion that finally culminated in an experiment performed by the great German scientist Anton de Bary, a man widely considered to be “the father of plant pathology.” Dr. de Bary’s experiment was both simple and elegant: He inoculated half of a trial set of potato plants with late blight and left the other half uninoculated. Only the inoculated plants came down with the disease, while the others remained healthy. This experiment proved without a doubt that it was Berkeley’s micro-organism that was causing the blight. The results of de Bary’s work were published in 1863 and helped pave the way for the acceptance of Louis Pasteur’s landmark Germ Theory of Disease, which was postulated a few years later.
So the upside of the potato famine was that it forced the scientific community of the day to rethink its inadequate theories of what caused plant diseases and accept a totally new paradigm. Knowing the actual cause of a disease is the vital first step in formulating meaningful management protocols. Some of the effective management techniques that followed, though not immediately, included the development of fungicides and the breeding of resistant varieties.
Think about it. The fact that we now have effective treatments for diseases in plants, animals and humans is very likely due to the revelation that a micro-organism was the cause of an important disease, in this case potato late blight. People, their animals and their crops are healthier today all because the scientists back in the day set out to understand what was causing a new and devastating disease of potatoes. Their work opened the gateway to a completely new way of interpreting our world.
Progress has been made but, unfortunately, late blight still remains the most important disease of potatoes worldwide.