Introduction

The Rust and smut fungi, growing on crop plants, have probably been observed since the beginning of agriculture. However, it is only the rust fungi that has been specifically recorded very early in written historical time. The rusts is specifically mentioned in The Bible and by the ancient Greeks and Romans. However, neither the Greeks or Romans had a specific name for smuts and The Bible called all sickness of grains "blasting" or "mildew", so smut was also not specifically mentioned. It would not be until around 1700 that the English agriculturist, Jethro Tull, described what surely must have been smut on wheat:

"Smuttiness is when the grains of wheat, instead of flour, are full of a black stinking powder."

Today, we will discuss these two groups of diseases and the impact they have had on western cultures. We will begin with the rusts fungi since they have had the most impact, historically and economically, and continue to have significant impact. The species that we will discuss is Puccinia graminis, one of three species that cause Wheat Rust. The Wheat Rusts pathogens are probably the earliest recorded pathogens. We will also discuss Hemileia vastatrix, the cause of Coffee Rusts, a pathogen that changed the drinking habit of England and gave rise to an English stereotype.

The rusts belong to the Basidiomycota, the division of fungi to which the mushrooms belong. Although the rusts attack a large number of seed plants and even some ferns, it is the rusts' diseases on the various grains that have been most frequently described in historical records. The common name rusts is based on the "rusty" colored blotches that is present on the stems and leaves from the urediospore stage in this group of fungi. Recent archeological digs in Israel discovered spores of Wheat Rust on grains dating back at least 3000 years. Rusts diseases, along with a few other types of plant diseases, have clearly been recorded in the Bible, and the ancient Greek writings of Aristotle, and his student Theophrastus, who has been called the father of botany because of his early contributions to plant science. In his Historia Plantarum (History of Plants), Theophrastus described rusts on grain crops, in meticulous details, twenty two centuries ago. The Greeks and Romans actually made a good start in attempting to understand plant diseases. However, the dark ages soon followed and it would be a thousand years before progress in understanding of diseases would be made. Even as recently as 1800, it was believed that fungi found on diseased plants were part of the dying tissue of the sick plant, and it would not be until 1861 that Anton de Bary would demonstrate, conclusively that the Late Blight of Potato disease was due to the fungal pathogen, Phytophthora infestans.

Before describing some of the impact that this group of diseases has had and continues to have on the world, let us look into the uniqueness of the life history of this fungus. Unlike most parasitic fungi, or fungi in general, the rusts do not have only one spore (sexual or asexual), or two spore (sexual and asexual) stages and a single host, they may have as many as five spore stages and may have two hosts. The species that we will be using as an example of a grain rust, Puccinia graminis (Wheat Rusts), is such a rust. In order to complete its life history, this species produces the following five spore stages:

The urediospores and teliospores are borne on wheat while the spermogonium and aeciospores are borne on what is referred to as the alternate host, barberry. The basidiospores are not borne on either hosts, and is the transitional stage that initially infects the barberry host. During the early spring, the aeciospores will infect the wheat plant. Infection of the wheat occurs in both the stem and leaves. Entry into the host occurs when the spores germinates and enters the plant through openings called stomata (Figure 1). Stomata are pores on the surface of the herbaceous parts of plants that allow for gas exchange to occur. However, these openings also provide an avenue for pathogens such as the rust fungi to enter. Once entry into the wheat plant has been accomplished, mycelium will grow and begin to absorb nutrient from the plant. The mycelium in the host plant will give rise to clusters of urediospores, with each cluster being produced in a uredium. As the urediospores develop, they will burst the epidermis, exposing the characteristic, rusty-colored urediospores on the surface of the plant (Figures 2 and 3). This stage is a "repeater stage" and is the most damaging to the wheat. The urediospore can infect other wheat plants throughout the spring and early summer. During late summer, just before fall, the uredium gradually converts into the telium and begin to produce the two-celled, thick-walled teliospores. The conversion is readily observed as the rusty-brown uredium becomes black as the teliospores are borne (Figures 4[image from Courtesy Cereal Disease Laboratory Archives, copyright-free] and 5).


Fig. 1: Stomata on epidermis of plant	Fig. 2: Urediospores breaking through epidermis of plant	Fig. 3: Rusty colored uredia on wheat stem.

Fig. 4: Black telia on wheat stem	Fig. 5: Thick-walled, two-celled teliospores on wheat.

The teliospore stage, with its thick wall is the over wintering stage and will remain dormant for the winter. The following spring, each cell is capable of germinating to produce basidia and basidiospores (Figure 6). What happens next is somewhat unusual. Instead of infecting the wheat plant, again, the basidiospores, instead, infect the alternate host, the barberry and produces spermogonia on the upper surface of the barberry leaves. Each spermogonium consists of what is interpreted as female (receptive hyphae) and male (spermatia) (Figure 7). These structures may be thought of as "eggs" and "sperms", respectively. Thus, this is the site where the "sexual act" takes place. In order to get the spermatia and receptive hyphae to "meet", the spermogonium exude a sweet, nectar that attract flies (Figure 8). As a fly goes from spermogonium to spermogonium, drinking the sweet liquid, spermatia become attached to the fly and becomes deposited on the receptive hyphae and begins to go through its sexual cycle. Unless this event takes place, the aeciospores, the next spore stage, will not form. The role of the spermogonium was unknown until 1927, when a Canadian plant pathologist, John Craigie, determined the function of this part of the life cycle. The aecia with the aeciospores form on the lower surface of the barberry leaves (Figure 9). The aeciospore is the stage that will reinfect the Wheat plant and the cycle then starts again.


Fig. 6: Teliospore germinating to produce basidium, with one basidiospore still attached.	Fig. 7: Spermogonium with receptive hyphae and spermatia	Figure 8: (Courtesy of Cereal Disease Laboratory Archives, copyright-free) Spermogonium on Barberry leaf, showing nectar droplets.

Evidence of the early knowledge of Wheat Rust can be found in the Bible, in the story of Joseph, 1800 years before the birth of Christ. According to The Bible (King James version of the Old Testament), Joseph was a gifted man who had the ability to interpret dreams. He was the eleventh son of Jacob, a wealthy farmer with land and domesticated animals. However, Joseph's brothers were jealous of this ability, but became especially mad when he told them of a dream in which they would all, one day, bow down to him. They became so angry that they sold him into slavery to an Egyptian trader. To explain Joseph absence, his brothers told their father that Joseph had been devoured by a wild beast, and smeared goat's blood on his cloak as evidence.

Upon reaching Egypt, Joseph was sold by the trader to a captain in Pharaoh's army. Although a faithful servant, he was imprisoned for adultery, a crime of which he was innocent, after he had refused the advances of the captain's wife. While in prison Joseph's reputation as an interpreter of dreams became well known, and it was during Joseph's time in prison that Pharaoh had two strange dreams that he was unable to interpret. In one dream seven fat cows came out of the Nile, followed by seven thin cows. The seven thin cows then ate the seven fat cows. In the second dream, seven fat ears of grains came upon one stalk followed by seven thin ears that was blasted by the east wind followed after them. He believed his dreams to be visions, and called upon all the wise men of Egypt to interpret his dreams. However, none were able to find meaning in his dreams. One of Pharaoh's servant, who had been befriended by Joseph while in prison remembered Joseph's skill of interpreting dreams and told Pharaoh of this ability.

Joseph interpreted Pharaoh's two dreams as one. Joseph interpreted Pharaoh's dream as a prophecy of seven good years where food would be plentiful because the grains would grow in abundance, but that this would be followed by seven years of famine when the grain crops would fail due to crops being "blasted by the east wind". "Blasted" here is interpreted here as the wind blowing rusts spores on the grains. For interpreting his dream Pharaoh rewarded Joseph by making him ruler of all the lands of Egypt. Only Pharaoh would have more power. To prepare for the prophesized famine, Joseph stored surplus grains in granaries that he had built, during the seven years of prosperity. So it came to past that during the next seven years famine was widespread around Egypt, Joseph's preparation spared Egypt, itself from the same fate.

In Canaan, Jacob and his family were now starving due to the famine. Learning that there was food available in Egypt, Jacob sent, with the exception of Benjamin, all of his sons there to buy food. There Jacob's sons, not recognizing Joseph, bowed before him as Joseph had prophesized, when they asked to purchased food. However, remembering what his brothers had done to him when they were younger, Joseph decided to test them to see what kind of people they had become. Joseph accused them of being spies but did give his brothers the grain they wanted on the condition that they must bring back their youngest brother Benjamin. To ensure that they would return he kept one of the brothers, Simeon, prisoner until their return. Joseph welcomed them, gave them more grain and sent them on their way home. On their way home, a horseman came along and said they had stolen a silver cup from his master. The cup was found in Benjamin's sack. Joseph told his brothers that as punishment for stealing the silver cup, Benjamin would become his slave. Upon hearing this, Judah, the brother who sold Joseph into slavery, came forward and made a plea for Benjamin to be released because of the grief that this would cause to his father, and asked that he take Benjamin's place as Joseph's slave instead. Joseph could see that his brothers had changed and revealed himself to them. Joseph then told his brothers to return with their father and gave them land of Goshen.

In addition to recording what must have been the first famine due to Wheat Rust, there are many other questions that may be pondered. The above story also tells of how the Hebrews first came to Egypt. When the Hebrews first entered Egypt, they were well respected people, but eventually they would become the slaves of the Egyptians until the mass exodus from Egypt that was led by Moses. While wandering in the desert, the Ten Commandments were issued to the Hebrew by Moses. After 40 years in the desert, the Hebrews would conquer the Canaanites and take the land that Moses had prophesized would be theirs.

If the rust epidemic did not occur, how much of the above events would not have happened? Would Joseph ever have been released from Pharaoh's prison? Would the Hebrews have ever come to Egypt? If not, would there have been a Moses or the Ten Commandments?

The Roman wheat farmers were plagued by rusts. As was the case in many unexplained events that occurred at that time, the Romans created a god, Robigus, the rust god, who was honored in the Robigalia, a religious ceremony practiced for over 1700 years, which involved sacrificing reddish colored animals, such as dogs or cows so that the god would spare their grain. The origin of this ritual lay in the belief that humans were punished with rust-infected crops following an incident in which a 12 year old boy caught a fox in his father's chicken coop, and sadistically tied a bit of straw to the fox's tail and set it on fire before releasing it. As punishment, the god Robigus destroyed the wheat crop with an illness that left the plants with reddish-brown lesions as if burned by fire. Every Spring, on April 25th. since 700 BC until the decline of the Roman Empire, a ceremony was held to appease Robigus and induce him to hold back his vengeances.

Not all wheat farmers followed this belief. Many followed the advise of Cato, The Elder, a respected writer of the time, to plant wheat in areas where there was not "fog and mist". Although Cato's advise was sound, by this time, it was becoming impossible to follow. The weather in the Mediterranean region was changing. Through historical writing and the study of growth rings of old trees in the Mediterranean area, it is known that the climate, the first three centuries after the birth of Christ, were unusually wet, leading to conditions favorable for the spread of wheat rust. This weather was undoubtedly responsible for heavy losses of wheat due to wheat rust. With these losses came hunger, discontent and famine. Disease soon followed. These conditions from within, as well as other problems, the Roman Empire, in time, fell to invading armies. I must emphasize here that while the wheat rusts and probably other crop pathogens played a role in the fall of the Roman Empire, other, probably more important factors were also involved.

Even prior to the discovery of the germ theory, farmers were aware of plant diseases, and were able to make certain conclusions based on their observations, even if they were ignorant of the cause of the disease. In the case of the Wheat Rust they noticed that this disease was often worst when there were barberry bushes nearby. By 1600, in France, the first effort was made to control rust by eliminating barberry bushes, even though there was not any tangible evidence that they could find connecting the two. Keep in mind that this was 200 years before Anton De Bary's discovery that fungi were capable of causing diseases. This practice was maintained when Europeans settled in the New World, although they did bring the Barberry plants with them since it was a source of tool handles and yellow dyes for the colonists. However, even if they did not, Wheat Rust would still be a problem since there are two native species of Barberry, in North America.

Despite this discovery, an understanding of Wheat Rusts was slow in coming because of the lack of understanding that there were five spore stages. Once again, It was Anton de Bary who discovered all of the spore stages and determined that the disease required barberry as an alternate host.

The discovery that Barberry is the alternate host for Wheat Rust was a rather important discovery in trying to control Wheat Rust. Why? If we remove the Barberry plant, the teliospores may be produced and survive the winter, but the basidiospores will not have an alternate host to infect. The urediospore cannot survive a harsh winter and will also die. Thus, the Wheat Rust disease is ended. There was a program that was developed, in the United States, in 1918, and continued for decades, to eradicate the Barberry. This program was started to destroy Wheat Rust, but also was used as a means of employing large number of people during the Great Depression, in the 1930s. There were many people that worked their way through college, MS, and Ph.D. by working for the government in eradicating barberry plants. How important is the Barberry? In 1920, in the Mississippi Valley, a circular area of 10 miles of Wheat was virtually destroyed. Agriculturalist searching the area found a single bush of Barberry, which was responsible for the damage.

Programs to eradicate the barberry were also carried out in some European Countries where they were very successful, and although, the program in the United States may have been very important in providing employment to a lot of people, it unfortunately, did not rid us of Wheat Rust which is still with us, today. Why did barberry eradication, in North America, fail to rid North America of Wheat Rust but yet was successful in European countries? The problem was that the wheat growing areas in some of the Gulf States and Mexico had winters that were not as harsh as on the northern plains. Because of the relatively, mild winters, the urediospore stage was able to over winter and during the following spring, urediospores were dispersed in the wind, northward from Texas and Mexico, to the Canadian Wheat fields. Although, eradication of barberry didn't rid the country of Wheat Rust, it did remove a significant source of infection and did delay any potential Wheat Rust epidemics for several weeks.

It was not until varieties of Wheat, resistant to Wheat Rust, were bred that this disease was placed under some measure of control, but even this was not easily accomplished. There were a number of resistant Wheat varieties bred. This was necessary because it was realized that there were a number of different races of Wheat Rust. Even in 1918, when the Barberry eradication program started, it was known that there were 28 different races of Wheat Rust. Each race of rust could be rendered harmless by a particular Wheat variety that was developed, but each Wheat variety was not resistant to all or even several of these 28 races. So a large number of Wheat varieties had to be developed for this reason.

To avoid annual Wheat Rust epidemics, the plant pathologists planted all of the different varieties of Wheat that are resistant to Wheat Rust to see which of the Rust races predominate in any given area. In this way, the plant pathologists determine which would be the safest variety of Wheat to plant each year. Thus, each year it becomes a matter of luck as well as making an educated guess as to which of the cultivated varieties of resistant Wheat should be planted. A lot is dependent on the correct decision, 50 million acres of U.S. Wheat. Fortunately, this method has so far been pretty successful.

At the same time that Europe was plagued by a number of plant diseases, between 1845-1885, another disease organism, belonging to that group of fungi that we call the rust, was attacking the coffee-trees in Ceylon (presently Sri Lanka). The Coffee Rust fungus was first recorded by the Reverend Miles Berkeley, who was sent a collection from the Royal Botanical Gardens at Peradenija. Berkeley's collection of fungi from Sri Lanka was already quite large, containing 1100 collections, and this collection was different from all of them. Berkeley believed this to be a new species and named it Hemileia vastatrix and published it in November 1869.

Hemileia was first found on coffee, in 1875, in the Madulsima district where it was associated with premature leaf drop. Even at this time it was already of concern since it had affected three acres of coffee plants. When Berkeley learned of this disease and the fear associated with it, he thought these fears to be well grounded since he had already seen what the Late Blight had done to potatoes. In his publication concerning this species, Berkeley even suggested immediate application of sulfur because this disease would be difficult to combat once it had been allowed to spread. The reason for this was because so much of the disease was within the leaf tissue that it would be difficult to combat. Unfortunately, no one paid attention to the fears of some of the growers and Berkeley. That was in 1869. In five years the coffee-leaf disease had spread over the whole island and no plantation was free of the disease.

The symptoms of the disease were subtle. The disease would initially cause premature leaf drop, during the first season, but the following season, the trees grew new leaves and all appeared normal. Pictures of the symptoms of this disease may be viewed here. However, leaf drops became more and more frequent and in the next five years, coffee production dropped by more than 50%. However, action by the government was slow. A commission was set up to study the disease. By this time the disease had spread to southern India and Malaysia and was menacing the entire coffee industry in the East. Two studies were done. The earlier one was undertaken by Daniel Morris.

Morris was not trained in mycology and had little understanding of fungi. However, he did know of Berkeley's suggestion that sulfur should be tried. Following application of sulfur he noted that the superficial fungal growth that could be observed on the coffee plant was eliminated and that the diseased plants looked better. However, this effect was temporary and the disease soon returned. Repeated application might have eliminated the disease when it was first observed in a small area, but with the Monsoon winds blowing the spores throughout all of the plantations, spraying a few infected plants would have little effect on this fungus. Also, Morris had misinterpreted the symptoms that were observed on the diseased plants. These and other questions would be answered by Morris's successor, Harry Marshall Ward.

Ward, unlike Morris, was trained in plant pathological methods and was a student of Anton de Bary. Upon his arrival in Sri Lanka, he could not help but be impressed with the array of fungi and other organisms that were present in. Ward isolated spores from fungi that were found the coffee plant. He found no less than 51 different fungal spores on the coffee plant which he was able to germinate and grow on a sugar gelatin substrate. One fungus included the external growth that Morris had observed to be covering the coffee plant, but Ward was able to demonstrate that this was not the fungus that was responsible for disease of coffee. Ward also observed that the actual coffee rust was largely an internal parasite that grew through the stomata of the leaves. Ward would also discover the other stages of spores that grew from the coffee rusts, but did not discover all of the spore stages, which today still are unknown.

Although Ward would go on to discover the presumed origin of the coffee rust, and the reason for the "sudden" spread, he learned early that little could actually be done about the disease itself. When the plantation owners carved out their estate, they cut down many of the tall trees that would have sheltered them from the Monsoon winds and the rust spores that were disseminated as well. This displeased the plantation owners since they wanted Ward to discover a method by which they would be rid of the disease.

In its natural environment, the rust, was not a significant pathogen since it was an obligate parasite on the coffee plants and the coffee plant were sparsely distributed. However, as the land was cleared, and other species eliminated in favor of the coffee plants, this provided the ideal situation for an epidemic of the coffee rusts. Because now, there was continuous acres of coffee plants and what discontinuity was present, was short, which was not too far for the wind to carry to the next plantation. There was not even mixed cultivation which would have broken the rusts cycle since it would not have been able to attack another crop. Like Morris, Ward also suggested spraying sulfur, but at a specific time during the life cycle of the fungus, i.e. during the germination of the urediospore, when the fungus was most vulnerable. Once inside the host, the spray would be almost useless since it would not penetrate the leaves of the plant. This solution did slow the rate of destruction and raised the yield of coffee for a short time, but Ward realized this would not stop the rusts since by this time it was too late because of the vast number of infected trees with the astronomical numbers of spores that were produced from them, the disease could not be stopped.

Prior to the Coffee Rust, coffee was an important part of the social and political environment in England. By 1675 there were approximately 3000 coffee houses, in London, which became gathering places for social, political as well as religious discussions. It was a place where the daily papers, desks and writing material were available. Lloyds of London, an international insurance company started in a coffee house, in 1690. So many ideas were discussed in coffee houses that King Charles II labeled coffee houses "seminaries of sedition" and tried to have them all closed. However, the popularity of coffee was such that when news of his edict was learned, there was so much protest that Charles was forced to rescind his order. So eventually when the Coffee Rust destroyed the coffee plants in Sri Lanka, Java, Sumatra and eventually spread to Arabia, Liberia and Africa. The British, no longer able to grow coffee, simply gave it up, and began growing tea in Sri Lanka. Thus, this is why Indian tea now is the main stimulant consumed by the British, and the drink that we now associate with England, but this was not always the case.

Today coffee is grown mostly in the new world tropics, i.e. Columbia, Brazil, etc., and for over 100 years they were successful in excluding the coffee rusts. However, these countries now are also confronting the coffee rust. In 1970 the coffee rust was inadvertently introduced into Brazil and has now taken its toll on coffee. An intensive spraying program has controlled the disease somewhat, but with the political unrest that occurs in that part of the world, quarantine has largely been unsuccessful. Some newer means of controlling the coffee rust has emerged since Marshall Ward, but none which can be regarded as successful. Breeding programs have produced rust-resistant cultivars of coffee and other natural species exist, which are also resistant, have been cultivated, but neither have been desirable since the coffee produced is of a poor quality. The loss of desirable qualities in a crop is a common result of breeding resistance to diseases.

The realization that the disease could have been treated so easily brought about the concept of "preventive" treatment of plant diseases that are largely internal. As was the case in other crops that we have discussed, genetic uniformity was again one of the reasons that led to the destruction of the coffee crop. In the case of the Coffee rust, crop rotation, changing to a different crop at different times of the year would have broken the rust life cycle.

The literal meaning of smut is "dirt or excrement". However, it has come to mean something that is "filthy or obscene". Like the rust fungi, the smut fungi is also a member of the division Basidiomycota, do not produce fruiting bodies and produce basidia and basidiospores from germination of the teliospore. However, unlike the rusts, the plant pathologists war against the smuts have been a successful one. Although no mention is specifically made of this group of disease until 1700, most plant pathologists agree that with the number of spores that are produced by the fungus and the number of species that grow on crop plants that smut must surely have been known since the onset of agriculture.

Mathieu Tillet, a keeper of the mint, in France, was a man of many interests. One of these included studying the problems of farmers. In 1755, while observing the smuts on Wheat, Tillet discovered that there were two types of smut growing on Wheat: La carie or what the English called "Common Bunt" or "Stinking Smut". Grains infected with this type of smut seemed healthy, at first glance, but grains were actually filled with brownish balls full of a black, foul-smelling powder (Figure 1). In the second type of smut, the plants looked healthy enough, but were covered with a loose, black powder that readily blew away. Tillet called this le charbon or what the English called "loose smut" (Figure 2). The distinction between the two types of smut was verified a century later, in 1847, by Louis and Charles Tulasne. To honor Tillet, they named the "Stinking Smut" Tilletia caries.


Fig. 1:Seeds infected with Tilletia tritici (Stinking Smut), on left, and healthy seeds, on right. Courtesy J. Riesselman, copyright-free.	Fig. 2: Bermuda Grass infected with Ustilago cynodontis, an example of a loose smut. Note powdery appearance of plant covered with spores.

So Tillet was delighted when, in 1750, the Academy of Arts and Sciences at Bordeaux announced that a prize would be given for the best investigation into the smutting of Wheat. Through conversations with farmers and experiments on a small parcel of land that he owned, Tillet observed that when smutted Wheat seeds were planted, the Wheat plants that grew always were smutted regardless of when he planted, whether they were planted in manure or not or the weather conditions in which they were planted. From this observation, Tillet concluded that the smut was seed borne and that the black powdery spores were the cause of the disease. In addition, he experimented with washing the seed grains, in water, cattle urine and lye solutions. Although this did not prevent the smut from forming, the treatments did suppress the disease to some degree. For his work, Tillet was awarded for the best research concerning the smutting of Wheat. However, the science in his research was actually not that conclusive. Tillet's concept of washing the seeds before planting did lead other researchers to continue in this line of investigation. The most important being Prévost, who continued with washing seeds, fifty years later.

Prévost placed smut spores in water and observed them through his microscope, over a period of several days, and saw "stubby sprouts" growing from the black particles, i.e., germination of the teliospores. He guessed from this observation that the "pointed ends" of sprout somehow pushed their way into the soft tissue of the germinating Wheat seedling and destroyed the grain. However, Prévost never saw the mycelium growing into the plant, but in his observation of germinating spores did, accidentally, discover a means of destroying the infection on the seeds.

When Prévost germinated the smut spores in water that he had distilled, he observed that they did not germinate as readily as when he used well water, and when they did germinate, the "sprout" grew for several hours and then shriveled and died. Prévost believed that when he distilled the well water, an element essential to the growth of the spores must have been removed. Although this experiment successfully killed the fungus in his lab, it would be impractical for the farmer since they would not be able to distill the water when they watered their Wheat nor could he distill rain water. Because this line of experimentation proved impractical, Prévost was ready to abandon it when he happened to hear a boastful farmer's remark that there was no smutted Wheat on his farm and that there had not been any for years. By this time, many farmers had followed Tillet's practice of washing the seeds with various solutions, before planting. However, as was the case with Tillet, this did not stop smut from forming. What was this boastful farmer doing that others were not? Prévost's conversation with the farmer did not seem as though it was going to lead to a remedy to the smutted Wheat. Then the chance statement by the farmer led to the revelation. The farmer mentioned that he washed his seeds in a copper caldron while his neighbors used wooden vats. Returning to his lab, Prévost examined the still that was used to make the distill water in which the spores did not sprout. It, too, was made of copper. With further experiments, Prévost determined that the slightest amount of copper prevented germination of the smut spores.

In 1807, Prévost recommended soaking seeds in a copper sulfate solution before planting. Although farmers were slow to adopt his suggestion, the practice was widely used from about 1850 until 1900, when formaldehyde replaced copper sulfate. Formaldehyde was preferred since copper sulfate was found to injure or kill the embryo of the seed if carelessly used. Later mercury compounds were used and most recently hexachlorobenzene (=HCB). This method, known as topical chemotherapy, has been successfully used and has saved billions of tons of food material by killing the disease causing organisms before they can infect the plant. However, this method could not be successfully utilized in Loose Smut of Wheat.

The loose smut is not found on the surfaces of seeds, but instead infect the seed as it develops. Thus, the fungus is protected by the seed, itself. Chemicals that were initially applied to eliminate the fungus from the embryo usually destroyed the embryo of the seeds as well. For a long time a method discovered by Jensen, a Danish plant pathologist, in 1888, was used for controlling this disease. Wheat seeds were soaked in hot water. The soaking induced hormones to form in the embryo that protected it from the fungus. However, systemic fungicides have been developed that can successfully eliminate the fungus without harming the seed. To date, there has not been any known resistance, by the smut fungi, to the fungicides that have been developed.

I was unable to find any verification about the story that I am about to tell, but thought it was interesting enough to tell, anyway. Once Wheat has been contaminated with Stinking Smut, there is nothing to do but to dispose of the grain. However, an interesting story concerning the origin of the gingerbread man related to Stinking Smut was told in Famine on the Wind, one of the books cited below. It seemed that a baker ground the contaminated grains into flour and attempted to make bread with it. However, because of the horrendous odor of the bread made with contaminated flour, the black discoloration in the bread and the awful taste, he was unable to sell the bread. However, he did not want to waste the contaminated grain, but what was he to do? He experimented with ways in which he could disguise all of the distasteful characteristic of the flour until he came up with a recipe that his customers would find acceptable. He used molasses to cover the dark coloration of the flour, but what could hide the taste and odor? He finally came upon a spice that was both strong in taste and odor, ginger. Thus, the origin of gingerbread. An interesting story, but one that I was unable to verify, other than in the source I cited.

Aeciospore: One of five spore stages in some rusts fungi, e.g., Puccinia graminis. Spore stage produced on lower surface of Barberry leaves. Spore stage must infect Wheat Plant and cannot reinfect Barberry.

Basidiospore: Spore characteristic of division Basidiomycota. In rusts, one of five spores stages, e.g., Puccinia graminis. Stage borne from germination of teliospore and must infect Barberry, the alternate host.

Basidium: Structure on which basidiospores are borne, characteristic of division Basidiomycota.

Cato (The Elder): Well-respected Roman writer who recommended that wheat be grown in areas where there was not mist and fog. Unfortunately, at the time the recommendation was made, changes in weather patterns were beginning to take place and it was impossible to find an area to plant Wheat.

Common Bunt: Plant that may appear healthy looking, but grains actually filled with brownish balls full of a black, foul-smelling powder. Also referred to as Stinking Smut because of the foul-smelling odor.

Craigie, John: Canadian plant pathologist who discovered the function of the spermogonium, in the Wheat Rust life cycle, in 1927.

Hemileia vastatrix: Commonly referred to as Coffee Rust, it is an economically important species of rust, which ended commercial coffee growing in the Old World Tropics. Most Coffee is now commercially grown in the New World Tropics, where until 1970, the Coffee Rust was excluded.

Loose Smut: Smut diseases in which the plants looked healthy, but plants were covered with a loose, black powder that readily were blown away and dispersed by wind.

Mildew: As used in this lecture, another biblical reference to diseases of plants.

Prévost: Discovered that a copper sulfate solution could prevent germination of Common Bunt spores. Suggested treating seeds in copper sulfate, as early as 1807, and from 1850-1900 was the most widely used method to control Common Bunt disease.

Receptive hyphae: Element of spermogonium, in rust fungi. May be thought of as female portion of life cycle. Spermatia carried to receptive hyphae, by flies, in Wheat Rust. The mixing of the two different nuclei provides the continual genetic variation in the rusts that has made them difficult to with breeding of resistant varieties of Wheat.

Robigalia: A religious ceremony practiced for over 1700 years, which involved sacrificing reddish colored animals, such as dogs or cows to Robigus, the Rust God, so that he would spare their grain crops. The origin of this ritual lay in the belief that humans were punished with rust-infected crops following an incident in which a 12 year old boy caught a fox in his father's chicken coop, and sadistically tied a bit of straw to the fox's tail and set it on fire before releasing it. As punishment, the god Robigus destroyed the wheat crop with an illness that left the plants with reddish-brown lesions as if burned by fire.

Robigus: The Roman God of Rust. The Romans believed this God to be the cause of Wheat Rust.

Rusts: Common name of economically important pathogenic fungi, belonging to the division Basidiomycota. Common name given because of the “rusty” appearance caused by disease, in urediospore stage. Many species parasitic on grain crops. Characterized by lack of fruiting bodies, formation of basidia and basidiospores from germination of teliospores and having as many as five spore stages and two hosts, e.g., Puccinia graminis (=Wheat Rust)

Smuts: Common name of economically important pathogenic fungi, belonging to the division Basidiomycota. Common name given because of the black, powdery appearance of infected host plants, in teliospore stage. Many species parasitic on grain crops. Similar in characteristic with rusts, but having fewer spore stages.

Spermatia: Element of spermogonium, in rust fungi. May be thought of as male portion of life cycle. Spore-like structures that is carried to receptive hyphae, by flies, in Wheat Rust. The mixing of the two different nuclei provides the continual genetic variation in the rusts that has made them difficult to with breeding of resistant varieties of Wheat.

Spermogonium: One of five spore stages in some rusts fungi, e.g., Puccinia graminis. Stage borne from germination of basidiospores on upper surface of Barberry leaves. Sexual organ of rust fungi composed of receptive hyphae and spermatia. Function of this spore stage was not discovered until 1927, by John Craigie, Canadian plant pathologist.

Stomata: Pores that function in gas exchange, on surfaces of leaves and herbaceous parts of stems. Often provides fungal pathogen with means of access into plant.

Teliospore: One of five spore stages in some rusts fungi, e.g., Puccinia graminis. In Wheat Rust, a two-celled, thick-walled, spore that over winters and germinates to give rise to basidia and basidiospores.

Tillet, Mathieu: Determined, in 1755, two types of smuts actually occurred on Wheat, Common Bunt, also known as Stinking Smut and Loose Smut. Charles and Louis Tulasne, almost100 years later, would confirm this. Also, started idea of washing seeds before planting to clean away smut spores from seed surface, which he believed to be the cause of disease.

Urediospore: One of five spore stages in some rusts fungi, e.g., Puccinia graminis. Repeating stage of rust fungi. Can continually reinfect a host as long as conditions are favorable for growth of fungus. Spore stage causing most damage in host plant.

Most of this lecture was based on the following books. If you are interested in reading a more detailed account of the above stories, you may find them in Hamilton Library.

Carefoot, G.L. and E.R. Sprott. 1969. Famine on the Wind. Angus & Robertson Ltd., London.

Kavaler, L. 1965. Mushrooms, Molds, and Miracles. The John Day Company, New York.