Lecture 06: Diseases of Some Crop Plants

The Origin of Plant Pathology, The Potato Famine, and Other Crop Diseases.

Introduction

The Relevance of Plant Pathology

The problems of fungal diseases on plants were probably observed even while humans were hunter-gatherers (Agrios, 2005). However, it is generally agreed that during this period, when dependence was on natural population of plants, the extent of the damage due to diseases was variable and usually localized (Scheffer, 1997). During such periods when there were extensive losses due to diseases, the range for gathering could be extended in order to find sufficient food. When agriculture began and certain food crops were planted in small plots of land, with greater more plants per unit area than would be found in nature, the incident of plant diseases increased and in some years caused famines or at least greatly reduced the available amount of food (Agrios, 2005; Scheffer, 1997).

Grain diseases were recorded in the Bible, as Blast, Blight and Mildew. It is uncertain exactly what these diseases referred to, but it is guessed by some that they were referable to smut and rust diseases (Agrios, 2005).  In addition to the classification of naming of plants Theophrastus (372-287 B.C.) had expertise in other areas involving the study of plants, including plant pathology, but his expertise was  more limited in this area. However, Theophrastus knew that under certain climatic conditions fungal diseases were more likely than at other times, but believed that these diseases came about through acts of the gods when the farmers had sinned (Agrios, 2005).  The Romans had similar beliefs and thought that Robigus and Robigo, their god and goddess of grains, controlled rust disease of grains and held an annual festival, the Robigalia in order to appease them (Littlefield, 1981). More sophisticated ideas as to the cause of plant diseases were eventually offered, such as "the plants are dying of some unknown malady". While this still did not answer the question as to the cause of plant diseases, it at least did not attribute them supernatural entities. The recognition that a fungus growing on a dead plant was the actual cause of its demise was not easily demonstrated because, intuitively, it was thought by most scientists that the presence of a fungus was merely growth that occurred after the plant had already been stricken or died. As you will see it was not until the mid-1800's that the connection would be made.

There have been numerous occasions when plant diseases of crop plants had major impacts on people. There are many such diseases and many have fascinating stories. I would like to go over two of the more interesting diseases that were of historical and economic importance, at the times that they occurred. The two diseases that we will specifically discuss are the Late Blight of Potato that caused a famine in Ireland, in 1846, and the Downy Mildew of Grapes that almost caused economic ruin for the wine industry in the Mediterranean, beginning in 1865. These two diseases were caused by Phytophthora infestans (Mont.) deBary and Plasmopara viticola (Berk. & M.A. Curtis) Berl. & De Toni, respectively. These two species are classified in the phylum Oomycota. Although very fungal-like in appearance as well as in the economic losses that they cause as plant pathogens, the phylum is no longer classified with the fungi for various reasons that we have already discussed. Because of their significance, both diseases have been very well documented. We will discuss the Potato Blight first because this disease actually marked the beginning of Plant Pathology, the branch of botanical sciences that study the diseases of plants. In addition, we will also discuss Panama Disease, a disease of banana caused by Fusarium oxysporum Schlect. f. sp. cubense. This disease ended the cultivation of the Gros Michel (Big Mike) banana, the most popular cultivar (=cultivated variety) sold in the United States until the 1950's and is now threatening the Cavendish, the cultivar that replaced the Gros Michel and the one most commonly sold in stores.  

The stories of these diseases that are told here have come mainly from three sources (Carefoot and Sprott, 1967; Christensen, 1965; Large, E.C., 1940).

Phytophthora infestans and the 1845 Potato Famine in Ireland

Staples, Cultures and Civilization

When agriculture began, different cultures selected different staples on which their civilizations were built. For example, the Asian cultures grew rice and corn was the staple for the Mayans and Aztecs of Central America and Mexico. In Western Europe wheat and rye were the crops that were usually grown. A lesser known staple is the potato. Its place of origin was in the new world tropics, in the highlands of South America, between Peru and Bolivia. This is the crop on which the Incan civilization was based and the subject of part of today's topic on the origin of plant pathology. The potato plant was an ideal crop in many respects. The tuber, the part of the potato that is eaten, grows underground and originates from the swollen, underground stem of the plant where it is protected from the hazards of the above ground part of the plant. It is a complete food that is high in carbohydrates, proteins and vitamins on which the Incas were able to build their civilization. The use of the potato as the Incas' staple could be traced as far back as 400 B.C. in the Incan religious and agricultural records (Carefoot and Sprott, 1967).

The Introduction of the Potato to Europe

As was the case in many civilizations in the New World, the Incan empire was conquered by the Spanish Conquistadors during the 16th. Century for their gold, silver and jewelry. In their quest for riches, they also discovered the potato. The potato was brought back to Europe, not as a potential new crop, but as part of the provisions for the sailors on their long voyage home. Potatoes soon became a standard on their sailing ships because it was noted that sailors who ate potatoes did not suffer from scurvy. However, because of the poor storage facilities, most of the potatoes that were not eaten did not survive the trip. It was the few surviving potatoes that gave rise to the cultivar that we commonly refer to as the "Lumper"  or "Irish" Potato (Fig. 1). The latter name reflects its association with the Irish.

The potatoes were thought to have arrived in Spain around 1570 and from there was distributed through much of Europe and England. However, there was reluctance in accepting the potato as a new food crop. It would be another two centuries after its introduction before there would be any significant plantings of the potato for food. The reasons for not accepting it as a new food were varied. Many religious leaders discouraged the eating of potatoes because they felt that crops that grew in the soil, rather than on top of the soil, was not suitable for consumption by people. Also, since it was not mentioned in the Bible, there had to be something inherently evil about the potato. There was even a logical reason for not eating potatoes. Because the potato plant is a member of the Nightshade Family, which includes mostly species of plants containing alkaloid poisons, it was felt that the potato might also have these poison. This, in fact, is true! One of the very interesting characteristic of the potato plant is that the roots, stems, leaves, flowers and fruits of the potato plant are poisonous. The potato is the only part of the plant that is edible and even the potato can begin to accumulate the alkaloid poisons that are found in the rest of the plant if it begins to sprout and turn greenish with age. However, some people still experimented with eating different parts of the plant. The fruit of the potato plant was the most common part eaten. Aside from being poisonous, it was also very bitter. Based on the bitter taste of the fruit that was tried by many people, it was decided that the whole plant was worthless as a food crop. Despite these problems, the potato, nevertheless, eventually became accepted as a food crop, not just in Ireland, but throughout Europe. Farmers discovered that it was a crop that required little care, appeared to be very nutritious and because of its subterranean habitat, it was safe from invading armies which was one of the reasons it was adopted by the Irish. Prior to the potato becoming the staple of Ireland, the poor of Ireland consumed mostly rye, which was also true of most of the peasant people in Western Europe, but grains were often diseased and unfit for consumption, and the amount of grain available, after harvest, was meager when compared to the potato crop, which had high yields, even when grown in the boggy areas of Ireland. For these reasons, the potato became an important crop in Europe sometime during the 17th Century.  The potato was believed to be responsible, in part, for agrarian revolution of the 17th and 18th Century as well as for the population increase in Europe during this period. With the increase in population, the farmers went from subsistence farming to making a profitable living. Although the potato was, in part, responsible for the beginning of this prosperous time in Europe's history, that is only part of the story. Prior to this period, the European staples were rye, if you were of the peasant class and wheat, if you happened to be wealthy. The abandonment of these grains in their diet may also have played a major role in the increase of the European population. We will discuss this theory later in the semester.

The potato would not be introduced into Ireland until the mid 1700's, but by the 1800's the potato would become a major part of their diet, supplying them with 80% of their calories. The potato was also used as fodder for their farm animals that would supply them with milk, eggs and meat to supplement their diet. Thus, the Irish was totally dependent upon the potato for their food. Unfortunately, it was this dependence that led to the famine that would occur in the mid 1850's.

Relationship Between the English and Irish

The Late Blight of Potato was first documented in Ireland during the late Summer of 1845. Thus, the name Late Blight, and eventually would be responsible for the death of approximately one million people and the migration of another 1½ million people to other parts of the British Empire, Canada and the United States. The fungus caused a mildew to form on all parts of the plant, which led to the eventual death of the potato plant.

The population of Ireland in 1845 was approximately eight million. So the disease impacted more than a quarter of the Ireland's population. It was all the more devastating because during 1844, the potato crop had increased its yield, dramatically, and during the early Summer of 1845, it appeared to be one of the best harvest year for potatoes. However, without warning, the weather became more overcast and rainy for weeks and it was during this period that the potato crop throughout Ireland appeared to rot overnight. It was all the more frustrating for the Irish because there was nothing that they could do since the actual cause of the Potato Blight was unknown. It was the failure of the potato crop that in part led to the death of one million Irish peasants. If you have taken high school biology or have taken an introductory course in biology at some time during your undergraduate career, you have probably heard this much of the story. However, there is much more to this story and than just the failure of the potato crop which eventually led to these deaths. Remember that a combination of events rather than a single event is responsible for determining the path that history is to take.

There was already a great deal of negative interactions that occurred between the Irish and English, even prior to the crop failure. The tragedy of the famine was merely one more reason for the conflict between the English and Irish that goes on to this day. Also, it is not a simple matter of the English Protestants against the Irish Roman Catholics as the news media always seem to portray this conflict. The conflict is an old one that has been on going for centuries. In biology we tend to emphasize that the fungus, Phytophthora infestans, was responsible for the mass starvation that occurred, and it certainly was responsible for the failure of the potato crop. However, the Irish blamed the English for their dependence on a one crop staple.

Prior to the famine, one of the causes for the Irish resentment towards the English was the exorbitant rent that was being paid to people that were referred to as the absentee landlords. These landlords were English nobles who came into possession of the land, in the 1640s, when English forces under Oliver Cromwell invaded Ireland and seized Irish land. Although, the reason for the rent being so exorbitant was not illegal, even by today’s standard, it is certainly not a situation that any of us would want to be in. The landlords resided in England and charge of the land was actually under the control of agents of the landlords whose job was to lease the land. Thus, the name absentee landlords. The lease from the agent usually involved a hundred acres. The man who leased from the agent would then sub-let most or all of the land in five acre lots at an even higher rental. These plots were then further subleased into smaller portions and rented again at still higher rates. At the bottom of the sub-lets, with a quarter acre, was the Irish peasant who had to grow enough to feed a family and pay the rent on the land. The Irish peasants were also the poorest people of all the renters and were paying the highest rate per unit area in renting the land. Although the potato was the only crop that the Irish peasants grew for their own consumption, there were many other crops that were grown in order to pay for the rental of the land. Artist conceptions of life during and after the Potato Famine may be viewed from this link.

Why Adopt the Potato as the Staple?

Because of the exorbitant rent, there were often tenants that were unable to pay their rent or became rebellious. When tenants resisted eviction or rebellions occurred, English soldiers were sent in to burn down the homes and crops of the tenants, and often killed their pigs, which were kept for an emergency food supply in the event of food shortages. However, the potato had the advantage of being "hidden" from the soldiers so that there was still a food supply even after the soldiers had taken their food and burned what remained. In addition, as mentioned above, rye, which was the staple, until the mid 1700's, when the potato was adopted, could not be grown in adequate quantities to feed the Irish and much of what was available was often found to be covered with fungal growth while the potato grew in great abundance in soil-poor areas where other crops would not grow.

Once the potato became the established, staple crop, in Ireland, by 1800, the population of Ireland almost doubled, going from 4.5 to 8 million people by 1845. The potato was the main course at every meal for the Irish peasant and often may have been the only food for each meal. The typical Irish peasant ate 8-14 pounds of potato each day.  However, potatoes are nutritious and have substantial carbohydrates, as you might guess, and also proteins and vitamins. Although not the best tasting diet, this diet was forced upon the peasant farmers because they were poor in the extreme. Families typically lived in a one room, windowless huts with little furniture or possessions, on their quarter acre plots. Fortunately, the potato grew well in the moist, cool climate of Ireland which was similar to the South American highlands where it was native.

The cultivation of potatoes as a crop was also relatively easy and fast. Potatoes were grown by a process known as vegetative propagation. This procedure involved taking a small piece of the potato which included the "eye" which is actually a bud from which the potato plant is grown. The planted potato eye is often referred to as the seed potato, but is not a seed in the true sense of the word. This has a number of advantages. The eye has substantial food reserves to nourish the bud of the potato plant so that the the potato plant grew more rapidly than if it were started from true seeds. The other advantage to note is that the potato plants when grown in this fashion are genetically identical to the potato from which it was derived because it is a clone of that potato. So if the potato from which the seed potato was derived had the desirable quality that you wanted, then the potatoes produced from it will also have those qualities since it would be a clone of that potato. Whereas if you grew potato plants from actual seeds, which are products of sexual reproduction, each seed will give you genetically different potatoes and you could not be sure as to the quality of the potato crop. Remember that even though growing a cloned potato may have the advantage of growing a crop that will give you the most desirable characteristic for a potato, it also had the disadvantage of genetic uniformity, and this was one of the main reasons that all the potato crop was so susceptible to the Potato Blight disease. Once the disease struck one plant, it would surely kill all of the potato plants, in a farmer's field, because of the genetic uniformity of potato plants. The disease would then continue to the next field and do the same for the potato plants there. So you run a great risk when you grow genetically uniform, i.e. clones, crops of any sort. The Irish potato was already at great risk even if seed potatoes were not used. Remember that few potatoes survived the trip from South America to Spain, and upon its arrival, there were only a few individual that could be used for breeding purposes. Therefore, there was already little genetic diversity even before the potato became a major crop in Europe. By the time the Irish began growing potatoes, it must have already been very genetically uniform. In addition, the seed potato is more likely to harbor diseases than a true seed since the nutritious part of the potato from which the bud will get its food will also attract bacteria and fungi that may kill the bud. Seeds, on the other hand, have a protective layer to protect the young embryo and food supply from infection.

This then sets the background for the Potato Famine. Lets summarize the salient points. From 1800 to 1845 the population of Ireland almost doubled and became wholly dependent upon a single crop, with no alternative food source should that crop fail. You may think that it was very short sighted of the Irish peasants to be so dependent upon a single crop, but they had little choice. Other crops were grown and even farm animals may have been raised, but the Irish could not keep these for their own use. Instead, these crops and animals were used to pay the rent to the absentee landlords. If rent was not paid the farmers were evicted from their land and they would then surely starve to death. Selling the crops elsewhere was also not a possibility, because the English Corn Act specifically forbade the export of crops from Ireland, the farmers were forced to sell the crops in England and at a fraction of the cost they could have obtained if it were a free market. These other crops usually only earned enough to pay their rent.

Although I have presented here a number of reasons why the Irish were able to only have a single crop staple, this practice is not an uncommon one. There are currently over six billion people in the world today. Yet, most of the world relies on three staple crops: wheat, corn and rice. Also, even with our knowledge of the disadvantages of growing a genetically uniform crop, many of the major crops that we grow today are essentially clones.

The Blight of Potato Strikes

The summer of 1845 was like most summers, on the whole hot and dry, but then a change occurred throughout Europe. In Ireland, the temperature dropped from 1.5-7ºF below the average temperatures of the last 19 years. In just a few weeks, the potato plants became a blighted mass of decaying vegetation. When the farmers dug up the potatoes they were also found to be decaying, but some "looked" healthy, but they also rotted later in storage. The blight occurred throughout Europe and was not limited to Ireland, but it was disastrous in Ireland because of their dependence on a single crop. You should also bear in mind that even though the change in climate impacted other crops as well by decreasing their yield, the Late Blight affected only the potato. Crop failure of the potato had occurred and people had starved before, but none as serious as in 1845. So the farmers knew from the beginning that there was something new and evil that was killing their crops.

That the potato was dying was obvious, but nobody knew why. There were various reasons for this. At this time few of the common people were educated. Only the wealthy had the resources for an education and the leisure time after to look at the workings of the universe. Even these educated people were not necessarily scientists. For the most part, they were men trained in medicine or religion. These people did know of the existence of microorganisms, such as bacteria and fungi, since Anton van Leeuwenhoek had observed microorganisms, under the microscope, approximately 200 years prior to the Potato Famine. However, their place in nature were not understood. At the time of the Potato Famine, spontaneous generation was still used to explain the presence of the vast populations of microorganisms that could be found on diseased or dead tissue (Does this seem reasonable? After all, it was not known where microorganisms came from at the time). Thus, it was believed that the mycelium of P. infestans discovered on the dying potato plants and potatoes occurred after the death of the plant rather than the cause. 

However, 1845 was not the first occurrence of the disease. Local incidents of the disease had been known and documented as early as 1835 in the columns of the Gardeners' Chronicle and Agricultural Gazette, often in letters to the editor (Christensen 1965). That the disease was worst in some years than others could be deduced by the frequency of letters received. At some point a prize was even offered to the best explanation for the cause of the disease, and many explanation came forth. Some of the suggested included that the "little people" started it, that the land had become spent from over farming, some thought it was the Devil's work and sprinkled holy water in the fields to drive the Devil away. Some suggestions were more detailed and elaborate, such as the idea that because there was such a large quantity of potatoes grown than could be eaten, the excess was dumped out in the field, and for this waste God was punishing them by destroying their crops. Another elaborate and popular notion was that the "puffing, hooting locomotives that thundered up and down the countryside at the unholy speeds of 20 miles per hour were discharging electricity into the air" caused the blight. Popularity of this concept came about because some scientist lent credence to this theory by stating that static electricity in the air might be responsible since it was responsible for a number mysterious events

There were a handful of people that thought that disease was killing the dying plants, but what did they mean by disease? It was thought that the change in the weather caused the Late Blight. They reasoned that since people could become sick when the weather became cold and wet, that this was also making the potato plants sick. However, no one was able to say why only the potato plants were affected and not the grains. There were two scholars that even debated their ideas in letters to the editor. Dr. John Lindley, Professor of Botany at University College, in London, and also editor of the Gardener's Chronicle and Agricultural Gazette and the Reverend Dr. Miles J. Berkeley, whose hobby of collecting and studying fungi had made him an outstanding authority in this field. Both were well known in the community. Lindley theory as to the cause of the blight was very unscientific for a scientist. He argued that the potato plants had been growing at a great rate while the weather was normal and with the deluge of rain that came, the potatoes had sucked up water through their roots until they were already saturated with water and, not being able to get rid of the excess, the plant tissue became swollen and their tissues rotted away.

Berkeley, on the other hand, had a more plausible explanation, at least by today's standards. He had based his theory on his observations of leaves, from infected potato plants, which he had examined under the microscope. Berkeley observed that infected leaves were covered with a mold, similar to one he had seen on a sick onion, but was convinced that it was a new and different mold that was killing the potato plant in Ireland. Photographs of diseased potatoes and leaves, and a brief summary about the fungus can be found at this link. Shortly after his observation, Berkeley received a letter, from Dr. Jean Montagne, a physician in Napoleon's army and an old friend. With the letter were specimens of potatoes infected with the blight, and a drawing of the fungus. Berkeley was able to see immediately that Montagne's drawing of the fungus was the same as that which he observed on the blighted potatoes, from Ireland and became convinced that this new fungus was the cause of the blight. Although by today's standards, Lindley's theory would seem rather far fetched, it was Berkeley's theory that was deemed as rather bizarre. None of the readers of his letter to the local paper gave much credence to his theory. This was understandable since Berkeley was just giving his opinion based only on his observations. That there was a fungus growing on the plants was not in question. Lindley pointed out to Berkeley that this new fungus was an opportunistic fungus that was invading the dead tissue of the potato plant that had already been killed by the wet, as he had already proposed. These arguments would drag on while the blight continued to take its toll.

Anton de Bary

It would not be until 1861 that Anton de Bary, who is considered the father of modern plant pathology, that the question as to the cause of the blight was finally settled. He did what would be today a rather simple experiment, using the scientific method. He grew two groups of healthy potato plants which he subjected to the same cool and wet environmental conditions that favored the the blight fungus. To one group he applied the sporangia which he had collected from blighted plants while the other group, the control,  was kept fungus free. In a matter of a few days, the group to which sporangia was applied already showed signs of the disease and eventually rotted. In the control group, disease did not occur. This convincingly demonstrated that it was indeed the fungus which caused the blight and not saturation from too much water. It was this experiment that led other scientists to critically look at, not only diseased plants, but animal and human diseases as well. This was not only the beginning of plant pathology, but a year later, in 1862, Louis Pasteur's Germ Theory would replace concept of spontaneous generation of microorganisms in dead or dying organisms. So, de Bary's work actually preceded Pasteur's Germ Theory and should probably have been credited with this theory as well.

The Potato Blight returned year after year, despite cold winters that we would assume would destroy the fungus. How then did the fungus then survive the Winter to continue its devastation the following year? De Bary also determined that it was the farmers themselves that perpetuated the disease. The Late Blight fungus was able to survive the winter in the potato tuber. Tubers that were not consumed that did not appear to be diseased, but in some cases were actually infected, were placed in storage bins to be planted the following year. Under such conditions, if even a single tuber carried the Potato Blight fungus, the rest of the tubers in the storage could become infected. When planted the following year, the disease grew upward into the stem and leaves of the potato plants and finally produced sporangia and spores that would further perpetuate the disease. Another source was the rotted tubers that were discarded in the same fields that the potatoes were planted.  These tubers would produce potato plants before the potato fields were planted and became a ready source of the disease. This was the reason why entire fields of potatoes could seemingly become infected overnight. It was these practices that were responsible for the the devastating famine of 1845. The previous year, the potato crop had been a particularly good one. Far more potatoes were produced than could possibly be consumed by both the Irish peasants or their livestock. The surplus potatoes were stored and many discarded. Some were infected with the Late Blight fungus which grew slowly in storage during the Winter. The Blighted tubers were discarded in the Spring of 1845 along with surplus healthy tubers. Thus, the Late Blight Fungus was in place before the planting of the potato plants during the Summer of 1845.

Why did the Late Blight fungus suddenly destroy the potato plants of Europe in 1845? It is now known that the fungus is probably native to South America where it still cause disease on potatoes. With repeated voyages to South America, and the continued transport of potato, the Late Blight fungus was inadvertently transported with the potatoes and brought to Europe. This probably happened a number of times and during the long voyage the fungus often did not survive under the harsh conditions. However, it is thought that some faster crossings allowed the fungus to survive in the tuber which then became planted in Europe. This, together with the environmental conditions which favored the growth of the Late Blight fungus and the genetic uniformity of the potatoes throughout Europe was responsible for the sudden appearance of the disease.

Meanwhile in England and Europe

But what happened in England during the blight? Starvation was what killed the people of Ireland, but politics played a large role as well. When the disease struck in 1845, it was devastating, as you might imagine. When word of the disease came to the farmers, they dug under the wilted plants to find healthy tubers, but most had been, by this time, rotted. Fields were searched for healthy tubers. Even diseased tubers were saved, the rotted portions washed and the rest grated to produce potato flour. However, this was not nearly enough. Families starved and became weak and hungry. Out of desperation, the woods were combed for berries, nuts, fruits, ferns and roots for consumption. Many died as a result of poisons consumed from these plants. While the Irish peasants were starving, the landlord's agents piled high, carts with grains, and flocks of sheep, cattle and pigs, were driven to the export market. All the Irish could do was to watch them go.

Meanwhile in London, the one hundred and five Irish member of the Union of Parliament pleaded on behalf of their people for financial aide. However, the economist argued against this plan of action because this would violate economic principles and that the Irish must be left alone to solve their own problem. According to these experts, "Any tampering with the delicate balance of supply and demand would surely result in economic ruin". Despite the warning from the economists, Sir Robert Peel, who was leader of the Tories, the landowners' party, setup up an Irish Relief Commission, in November 1845, which bought in American corn. In order to do this he had to repeal the "Corn Act" which placed a high tariff on the import of foreign grains (The British referred to grain crops as "corn" and specifically called what we know as corn "maize"). This was done to protect the market value of domestic grain. By February 1846, food depots had been set up in Irish Seaport where corn was sold. In order to buy the corn, the Irish laborers were given government relief work on dock repairs, roadwork and drainage. This got the Irish through the 1845-46 season and prepared them for the planting season of 1846.

The fields were once again planted during the Spring and the fields were green with potato plants in May, but by June the rain came again, and by July there would be scarcely a good potato in the field. Once again, the scramble for food was on, in the woods, streams, roads and to the sea with much the same results. In addition to starvation, disease also came about mostly in the form of cholera, dysentery, scurvy and typhus. The workhouses and soup kitchens brought the people together from near and far thereby spreading the diseases. Although many of the healthy stayed to care for the sick and hungry, by this time, even they had decided to migrate elsewhere while their families were still well and strong. Emigration from Ireland has continued to this day, but now for different reasons. In the first ten years following the famine, one million died and almost two million migrated. The drop in the population of Ireland would continue well into the 20th. Century and it was not until the 1960s that an increase in the population would occur. However, the population of Ireland has never reached the 8 million achieved in the mid 1800s.  

Late Blight's Impact Elsewhere 

The failure of the potato crops also had other far reaching effects on English history. The Corn Law was passed in 1815, after the end of the Napoleonic Wars. The Corn Law imposed a heavy tariff on grains that were imported into Great Britain, thereby protecting the grains grown by the landowners, by keeping the price of imported grain high on the British market. The Whigs in Parliament had long argued that if this tax was removed the price of flour might be lowered to the level that would be affordable to the industrial workers. However, it would be Robert Peel, the head of the Tories, that would repeal the Corn Act, before the government changed from the Tory to Whig. As much as the repeal of the Corn Act displeased the landowners, this was the first step toward a policy of free trade, and because of this Great Britain became, during the last half of the 19th. Century, the center of world trade market for all commercial goods.

During the time of the Potato Famine was the first effort made by the state to aid its starving people. Before this time, victims of famine had been forced to fend for themselves. Personal disasters had been treated as a man's own concern or the concern of his family, but definitely not the responsibility of the state. This was also the same reasoning that occurred during the Great Depression in the United States.

The effects of the famine was also not limited to Great Britain. Its impact was felt throughout throughout much of the Western World. For example, Irish migration to the United States began. Although not well received when they first emigrated because of the fear of disease and bad feelings about admitting multitudes of people that were paupers, a great deal of bigotry met the Irish, especially from the militant Protestants who were all for deporting the Irish. Nevertheless, the Irish eventually, worked themselves into political power, often voting in bloc for the democratic candidates. The Roman Catholic religion at that time had a very minor role in spiritual affairs in this country, but today the Catholic Religion is one of the major religions in this country. Also, most Irish worked themselves up from the slums, and in 1960, we had our first Irish, Roman Catholic president, John F. Kennedy.

In Europe a great deal of change also took place. The Late Blight of Potato also struck throughout Europe. However, famine did not occur because of diversified agriculture. Nevertheless, hunger did come and prices did go up because of the failure of the potato crop. This caused discontent among the working class people throughout Europe. Riots and revolts occurred throughout the capitals of Europe. This was the time in which Karl Marx wrote the Communist Manifesto and Das Kapital, and there was growing sympathy for the causes of young radicals: Lajos Kossuth, a Hungarian revolutionary who fought for an independent Hungary and led the provisional government in 1849 until Russia intervened; Giuseppe Mazzini, an Italian patriot who fought for an independent and unified Italy; and Alphonse de Lamartine, French poet and minister of foreign affair in 1848. In Paris, Berlin, Vienna, etc., monarchies fell, republics were borne. New constitutions were granted. These events were all summarized by Carefoot and Sprott (1967). However, it should be emphasized again that while the Late Blight of Potato contributed to the above historical events, it was not the only cause for what occurred.

Although social changes occurred almost immediately, an end to the Potato Blight did not. The disease struck again in 1872 and again in 1879. Although John Lindley did observe, as early as 1846, that downwind from the copper works, in Swansea, Wales, the potato plants remained green and healthy, it would be many years later, in 1885, that a copper sulfate and lime solution, the Bordeaux Mixture, would be discovered that would be used to treat this dreaded disease.

However, even after the means to control this disease was discovered, there was one more major outbreak of the Potato Blight, which caused the death of many people as a result of famine. The famine took place, in 1916, in Germany, during WW I. Although it was now well known that spraying the plants with Bordeaux mixture would kill the fungus, all the copper that Germany had was being used for shell casings and electric wire. None was spared for the making of copper sulfate to spray the potato plants. This famine killed 700,000 people during the winter of 1916-17. Until that time, the war was going well for Germany. They were on the verge of defeating Russia, in the east and was readying themselves against England in the west. However, because of the starvation that was occurring, morale became very low in the German army and they were unable to launch a successful attack. This setback was all that was needed to turn the tides of the war against Germany. By 1917, the United States had entered the war and joined with the British and French, and would eventually defeat Germany. If not for the Potato Blight, at this period of time, the outcome of WWI may have been quite different.

Plasmopara viticola, the Cause of Downy Mildew of Grapes

The fungicide that would destroy the Late Blight fungus was not developed until 1885 and not specifically for the Late Blight, but instead to a related fungus, Plasmopara viticola, the cause of the Downy Mildew of Grapes.

Although Downy Mildew of Grapes was an important crop disease, fortunately it was not as devastating, in terms of human lives as the Late Blight disease. The Downy Mildew of Grapes also has a rather interesting story which involved a number of interconnected events which impacted several countries.

In 1865, the vineyards in the Valley of the Rhone began dying and each year the disease spread further. The disease began with reddening and yellowing of the leaves, which withered and fell. The rest of the plant was stunted. The grapes only partially ripened and by the following season, the plants were almost dead from the ground level up. Digging down into the roots, a M. Planchon readily observed the problem. The roots were swollen with irregular nodule at the base of the plants. Everybody could agree that this was the cause of the grape plants dying, but there was still the question as to what caused it. When news of the disease spread throughout France, there were a number of suggestions as to what caused the disease. Unfortunately, these were the usual, unhelpful suggestions. It was due to some miasmic (=disease) in the atmosphere. Some blamed the late frost of that year. However, Planchon examined the swollen areas of the root more carefully. Using a lens, he was able to observed that there were insects, specifically a species of aphid, that had invaded the roots. He also found eggs and adult females. The aphid was later identified as a new species of Phylloxera, which was named Phylloxera vastatrix. So this would be a job for the applied entomologists to handle.

The damage was done to the roots by the adult aphids sucking the sap from the roots. It is the puncturing and sucking that led to the abnormal swelling that could be seen in diseased plants.

The Phylloxera eventually spread throughout France and later to every wine making country in Europe. By 1885, it had also reached Algeria and Australia. In France, by 1875, it was causing a loss of about fifty million pounds sterling per year to the wine industry and approximately two and a half million acres of vines were affected.

Various desperate means were tried to ease the spread of the aphids. Vineyards were flooded in hopes of drowning the aphids and poisonous vapors were injected into the soil to gas the aphids. However, what eventually stopped the destruction of the the vineyards came from America.

The answer came from Charles Riley, at that time, an entomologist for the state of Missouri. He recognized the Phylloxera to be native to America and that it was probably introduced into into Europe on an American vine. It was at first thought to be different because the American Phylloxera attacked only the leaves of American grapes plants while it attacked the roots of the European cultivated grape (Vitis vitifera). Riley believed that the long association between the native American grapes and the aphid had developed a degree of balance that allowed both to coexist. By 1872, Riley had been to France to observe the dying vines and talked to French scientist and growers as to the significance of the fact that American vines in France seemed to be spared except for some galls on the leaves. What Riley suggested was for the French vineyards to use American root stocks that have become adapted to the Phylloxera and graft them onto French grape plant. Some growers were convinced by Riley and began importing root stocks from America. However, to many growers this was not acceptable.

Many French growers could not think of replacing the superior French vine stocks with American stocks,  believing that American grapes were raw and horrible. To the French wine connoisseur, it was an insult. Some growers felt if that was all that could be done, the wine industry was doomed anyway, and it would be far better to give up wine and go the way of the English and start brewing beer than to use American root stocks. This may seem like an over reaction since a solution was being offered that would save the wine industry, but you must realize that to the French, the vineyards and viticulture was more than just an industry, it was a part of their culture. So, only a few growers, at first, followed Riley's idea to remedy the problem of the aphids. This American root stock, however, did eventually solve the dilemma of the Phylloxera and appeared to save the French wine industry. However, another plague would soon replace it.

In America, there was also a fungus that grew on the native grapes, Plasmopara viticola. This fungus attacked the leaves of all species of grapes and attacked it much in the same way that the Late Blight attacked the potato. Plasmopara, in fact, is a related fungus belonging to the same phylum of fungi. However, it seemed to do little harm to the American grapes. In fact, it was even looked upon as beneficial by American growers. According to William Farlow, who was then the mycologists at Harvard: "Our native vines have a luxurious growth of leaves, and the danger is that in our short summers the grapes will not be sufficiently exposed to the sun to ripen". The Plasmopara appears at just the right moment to shrivel up the leaves so that the direct rays of the sun may reach the grapes. However, Farlow also added that if this fungus were to be introduced into Europe it would be quite a different story. In the moister climate, the attack on the grape vines might prove as disastrous as the Phylloxera, and the fungus was inadvertently introduced into Europe.

The fungus was first observed in France by Millardet and Planchon in 1878. It is not certain as when, where or how it had been introduced. Only that it was, and probably during the importation of American root stocks to counter the Phylloxera. The spread of the fungus was rapid and by 1882, it was in every wine growing district in France, and progressing fast over the vines of Italy and Germany. Symptoms of the disease include leaf spots that may be yellow or red, depending on whether the host is a white or red grape plant, respectively. The spots have an oily appearance that is surrounded with a halo that will diminish as the infection progresses. Under conditions of warm and humid evenings, undersides of leaves and other parts of the plant may develop a white, downy mycelium upon which zoosporangia are borne. It is from this stage that the derivation of the common name "downy mildew" originated. The yield of non-diseased grapes is dependent upon the severity of the disease. There may be a reduced yield to complete loss of grapes on the vine. To see pictures of diseased grape vines and grapes click here. A video showing zoospore release is also available on YouTube:

With this most recent of diseases, France had now endured almost 40 years of various plant diseases. However, the French would not give up because the diseased grapes were not just a crop that was grown by tenants as they were in Ireland. The vines were grown by the owners of the land and their very lively hood depended upon it. So the search to find a solution to the fungus continued.

By 1882, Pierre Millardet, Professor of Botany at Bordeaux University, and a student of Anton de Bary, had been carrying out research on the Downy Mildew fungus for several years and had clearly demonstrated that the infection of this fungus was much like that of the Late Blight. In October of that year, Professor Millardet was strolling through a vineyard. There had been much mildew in the locality that year, and he was surprised to see that the vines beside the roads were still leafy, while elsewhere they were bare. Examining these leaves more closely he found traces of a bluish-white deposit on them as though someone had treated them with some chemical. Millardet then went to see Mr. Ernest David, the manager of that vineyard. He learned from Mr. David that it was common practice for the vine growers to spray the vines beside the roads with a conspicuous poisonous looking substance to discourage passer-by from sampling the grapes. To do this, the grapes were sprayed with a solution composed of copper sulphate and lime. Mr. David had never really noticed that the sprayed plants remained healthy while those left untreated went the way of all other diseased vines.

For the next two years Millardet tested variations of the mixture used by Mr. David and found the copper sulphate best for not only controlling the Downy Mildew, but also the Late Blight as well. The copper sulphate is what we now call the Bordeaux Mixture, named for the area of France where it was discovered.

With the means to control the Downy Mildew of Grapes, the French vineyards were thought to be saved. However, this was not the end of France's problems. During the aftermath of the disease, something else happened that almost caused financial ruin to the wine industries of France and some of the Mediterranean countries, but this had nothing to do with fungi, insects or any other types of diseases of grape. Instead this came about through greed. When it appeared that the wine industry of France would collapse, some of the Mediterranean countries thought that they would be able to fill the void that France would certainly leave with the collapse of their wineries. The supply of available wine soon started to far exceed the demand and there was a glut on the market, which nearly caused financial ruin in all these countries.

Fusarium oxysporum : The End of the Banana Industry?

Introduction

The genus Musa is the herbaceous plant from which the various varieties of bananas are produced. It is native to South and Southeast Asia and was first thought to be cultivated in Papua New Guinea sometime between 8000 - 5000 B.C. (Wikipedia contributor). Today, bananas are cultivated throughout the tropics mainly for their edible fruit, but also for their fiber, banana wine and even as an ornamental plant (Wikipedia contributor).

The story as to how the fruit of the banana plant was first imported to the United States can be found in Carefoot and Sprott (1967). Their version was a "sanitized" one that I will supplement to make the story a more interesting and relevant one.

The discovery of the banana as an edible and desirable fruit, in the United States, did not take place until the 18th. Century, when sailors returning home from the tropics, told of the strange and delicious fruit. The first documented shipment of bananas to the United States did not occur until 1804 when the captain of the schooner Reynard bought 30 hands (=bunches) of bananas back from Cuba that he sold while docked at New York. For the next 60 years, there would only be sporadic shipments from the Caribbean Islands to the United States until in 1870 when the first bananas were imported. By 1898, 16 million hands of bananas were being imported.

The rise of the banana import business occurred rapidly, started by three men, Minor Keith, Lorenzo Baker and Andrew Preston. Keith, at first independently began not in growing bananas, but in building a railroad, in 1871, that started from Limòn, on the Costa Rican coast to the capital city in San José. Thousands of his workers' lives, including his two brothers, died from diseases such as Malaria, Yellow Fever and dysentry. This business venture would also prove disastrous since revenues generated from passengers fares and cargo shipments would prove insufficient to pay his debts. However, as early as 1873, Keith had started bananas farms and with the farms at close proximity to the railroad tracks, he could economically afford to transport bananas to Limòn where he began running a ship to New Orleans where the bananas were sold. The banana business proved so lucrative that Keith established the Tropical Trading and Transport Company. He would eventually own three banana plantations. Obtain titles to thousands of acres of land in Nicaragua, Panama and Columbia, and was shipping bananas into the United States at a rate of 2,500 hands/month.

At about the same time that Keith began building his railroad, Lorenzo Baker, who was a sea captain, had been shipping bananas from Jamaica since 1870. He was transporting 12,000 hands of bananas to Boston with each shipment. Selling the bananas, on commission, for Baker was Andrew Preston, a Boston businessman. Together, with other investors, they started the Boston Fruit Company. As with Minor Keith, the company was a success. However, by 1899, Keith had some financial setbacks and was forced to merge his company with the Boston Fruit Company to form the then powerful United Fruit Company (UFCO) that would virtually form a monopoly in certain regions of South America, Central America and the West Indies, forming a virtual monopoly in the banana market in certain regions that would come to be called Banana Republics. The name refers to a country that is totally dependent upon a single export product, i.e. banana, and is governed by a dictator controlled by American business. These were the golden years for UFCO. They owned all that was connected with exporting bananas to the United States and Europe, from the land where the bananas were grown, to the railroads and the ships that took them to market. They also controlled the dictators of the various countries where they did business, generating large profits and paying no taxes because of tax exemptions that they were given. In 1944 until 1954, a brief period of democracy came to Guatemala, where UFCO generated a large part of their income. At this time, unused land, mostly owned by UFCO, was redistributed to the people of Guatelmala. In an effort to regain control of the land, UFCO backed a coup that eventually toppled the young democracy and by 1954 was replaced with a puppet dictatorship that restored the land to UFCO. Dictatorships would rule Guatemala with the aide of UFCO until as recently as the 1970's when it was taken over by the Del Monte Corporation that has distanced itself from the practices of UFCO.

While the UFCO became rich and powerful, the native people gained little in the way of benefits. However, to be fair, they the people did obtain some benefits. There were schools that were started for the children of the workers, hospital care, as well as homes that were provided while they were working for UFCO, as their representatives were quick to point out. However, along with this was also imported, from the United States, the accepted racism that was occurring at that time. The best quality schools started were for "whites only" and segregation was common place with various places that became off limit to the native people. The rich became richer and a larger financial gap developed between them and the poor population grew, who grew larger in number and became poorer as well. For those of you who feel that government deregulation of business is a good idea, this is an example why it is not good to give private business interests a free hand to operate as they please.

While the growing of bananas proved very profitable, diseases plagued bananas from the beginning of its cultivation. There are a large variety of diseases that can infect the banana plant. Three of the most common fungal species are Fusarium oxysporum f. sp. cubense, the cause of Panama Disease, and Mycosphaerella musicola and M. fijii, the cause of Yellow and Black Sigatoka, respectively. Panama Disease is a soil borne disease and once it became established there is nothing much that can be done. The fungus work its way from the soil in the the roots where it would grow into the cylinder where the water and food transporting cells were located and plug up these cells preventing water and food movement. Toxins released by the metabolic activities of the fungus were also released that hastened the death of the banana plant. Dying plants could immediately be recognized by the reddish-brown discoloration of the internal stem tissue and the dead leaves that droops around the stem of the plants. Yellow and Black Sigatoka are also serious banana disease, but the latter disease is far more virulent and has a greater host range than the former, and is regarded to be the cause of significant financial losses. Both disease cause dark streaks on the leaves that will reduce the yield of bananas (Fig 5). We will emphasize the Panama Disease here since it is has had far greater impact than the other two diseases.

The Gros Michel (Big Mike) banana was the most popular variety when exportation of bananas began to the United States and Europe. However, this variety was also particularly susceptible to Panama Disease. A treatment that would rid the plant of the fungus has still yet to be discovered. Although the disease was known when banana plantations were started in the 1870s, it would not be until 1910 that the fungus would be identified as a Fusarium and described as F. cubense. Currently, the scientific name is Fusarium oxysporum f.sp. cubense.  However, UFCO managed to minimized its losses. It owned so much land that they were simply able to move their banana plants to a new location for replanting. Growers would also plow under, native jungles to gain more land for bananas. One temporary fix caused damage to the land, but suppressed the pathogen was silting and flood fallowing. This involved flooding the banana plantation land, under 2-5 feet of water, for about 6 months. After draining the soil, banana plants would be free of the disease for 5-6 years, at which time Panama Disease would return as prevalent as ever. 

 Despite the fact that the dictatorships were behind UFCO in some of the Banana Republics, the problems of the banana disease did not go away. In fact, they got worst. Mycosphaerella fijiensis, the cause of Black Sigatoka, is a species that was introduced to the Americas from Fiji, in 1972. Effective means of controlling these diseases have never been discovered. 

The above agricultural practices described above only delayed the inevitable. During the 1950s, Panama Disease would begin to wipe out most of the major Gros Michel (Figure 6) plantations of the world, and by the 1960s, these plantations would be nearly bankrupt. It was only then that the decision was made to switch to the Cavendish bananas (Figure 7), a variety that was resistant to Panama Disease. The Cavendish is currently the standard banana variety sold in the United States and Europe. However, during the late 1980s, a new variety of Panama Disease was discovered in Asian, Cavendish plantations that is as deadly to Cavendish bananas as the original variety was to the Gros Michel banana. This new variety has spread throughout Asia, the Pacific and Australia, where it has devastated the banana industry. Although, this new variety of Panama Disease has not reached Latin America, where most bananas imported to the United States are grown, according to Randy Ploetz, plant pathologist, at the University of Florida, it is only a matter of time before it does (Koeppel, 2011). The news for Cavendish bananas became grimmer when it was discovered in, India, in 2010 that the original variety of Panama Disease may somehow have been modified to enable it to infect the once resistant Cavendish variety (Koeppel, 2011). This new strain has been designated as TR4 (Tropical Strain 4).

It is only recently that the growing of the clones that are susceptible to these diseases has been been addressed. Currently, new varieties of bananas are being bred with seed bearing bananas that will be resistant to the various pathogens of bananas. Unless a varieties can be developed, we may not have banana in 10-20 years. 

There have been recent claims by several chemical companies claiming treatments for TR4, in August 2020, but no journal articles have been published verifying these claims. They include Tectus Matrix and Terra MG. However, Dale, et al (2017) published an article on their development of two genetically modified lines of Cavendish banana that is resistant to TR4. Unfortunately, I have been unable to find \follow up news on the growing of these TR4 resistant varieties pf Cavendish bananas.

Literature Cited:

Agrios, G.N. 2005. Plant Pathology. Burlington, MA : Elsevier Academic Press

Carefoot, G.L. and Sprott, E.R. 1967. Famine on the Wind. Rand McNally & Company, Chicago.

Dale, James, et al. (2017) Transgenic Cavendish bananas with resistance to Fusarium wilt tropical race 4. Nature Communications. http://doi.org/10.1038/s41467-017-01670-6

Koeppel, D. The Beginning of the End for Bananas. The Scientist. July 20, 2011.

Large, E.C. 1940. The advance of the Fungi. London, J. Cape

Littlefield, L.J. 1981. Biology of the plant rusts : an introduction. Ames : Iowa State University Press

Ploetz, R. C., and Pegg, K. G. 1997. Fusarium wilt of banana and Wallace’s line: Was the disease originally restricted to his Indo-Malayan region? Australas. Plant Pathol. 26:239-249.

Scheffer, R.P. 1997. The nature of disease in plants. New York, N.Y.: Cambridge University Press

Wikipedia contributor, Banana. Wikipedia, The Free Encyclopedia; 2011 Sept. 03, 04:32 [cited 2011 Sept. 07]. available from: http://en.wikipedia.org/wiki/Banana

Important Terms and Concepts

Anton de Bary: Considered to be the father of plant pathology and the person who demonstrated that the Late Blight of Potato was caused by a fungus that he named Phytophthora infestans. 

Bordeaux Mixture: A copper sulfate and lime solution first used to control Plasmopara viticola, the cause of Downy Mildew of Grapes, but also found to be effective against Phytophthora infestans, the cause of Late Blight of Potato. Mixture named for the university in which it was developed.  

Corn Law: English law during the 1800's that prohibited the import of foreign grains. Act was repealed during the potato famine.  

Fusarium oxysporum: Species that causes Panama Disease of bananas. Reason for replacing the Gros Michel variety of banana with the Cavendish variety. The Cavendish banana was resistant to this disease until a new strain of this disease was discovered that was capable of infecting it.

Phytophthora infestans: Species of "fungus" causing Late Blight of Potato.

Late Blight of Potato: Disease of potato caused by Phytophthora infestans that led to a famine that caused the death of approximately one million people in Ireland and another one million to leave Ireland.

Pierre Millardet: Professor of Botany, University of Bordeaux, during late 1800s. Credited with discovery of Bordeaux Mixture that controlled Plasmopara viticola, and saved wine industry of France.

Plasmopara viticola: Species of "fungus" causing Downy Mildew of Grapes.

Downy Mildew of Grapes: A water mold that caused disease of grape plants that almost brought economic ruin to the French wine industry until a discovery of a treatment for the disease.

Reverend Dr. Miles J. Berkeley: Amateur mycologist who believed that the fungi found on the blighted potatoes during the potato famine was the cause rather than the result of the disease.  However, his idea was ignored.

UFCO: Acronym for the United Fruit Company. The banana company had a monopoly in the banana business, in South and Central America, and the West Indies, from 1900 to around 1970.

Learning Goals

1. Why didn’t plant pathogens impact hunter-gatherer societies?

2. What were early ideas as to the cause of diseases?

3. Who was credited with determining the causes of diseases by microorganisms?

4. Where is the potato plant native and how did it get to Europe?

5. Why did the Irish People adopt the potato as a stable and why did this turn out to be a bad thing?

6. Why were/are the English often said to be responsible for the deaths of a millions people in Ireland during the potato famine?

7. Why did the Phytophthora infestans potato blight of 1845 impact Ireland more than the European countries?

8. The potato blight literally destroyed all of the potato crop in Ireland and Europe? Why was the disease so devastating?

9. Despite all the misery and death that resulted from the potato famine, some good came about as well. What were some positive outcome?

10. Who was Anton de Bary? What knowledge did he contribute to the cause of the potato blight?

11. About 700,000 people died of starvation, due to potato blight, in Germany, during World War I, even though a treatment was known by this time. Why did this happen?

12. What disease does Plasmopara viticola cause and how was it first introduced into France?

13.  After a treatment was discovered for P. viticola, why did financial ruin of the wine industry still occur in Italy and France?

14. What was the name of the reagent that was finally able to treat this disease as well as the potato blight and who discovered it?

15.  What is an inherent problem of cultivating all banana varieties, with respect to diseases?

16. What was the major fungal disease that the United Fruit Company had to deal with when they began growing bananas that is still a major problem today?

17. What were some of the unethical business practices carried out by the United Fruit Company?

18. How did United Fruit handle the problem of fungal diseases of bananas?