Category Archives: Phytophthora infestans

Anton de Bary – the Father of Plant Pathology

Yesterday was the birthday of Heinrich Anton De Bary (1831-1888) – the founding father of plant pathology (the study of plant diseases). De Bary was a model scientist: an inspiring teacher – gifted with intelligence, thoroughness and vision. His extensive studies of fungi and cyanobacteria were landmarks of biology. He was the first to unambiguously demonstrate that microorganisms were the cause and not the consequence of plant diseases.

A botanist’s heart in a physician’s body

Anton De Bary was born 184 years ago, on January 26th, 1831 in Frankfurt/Main, Germany. His oddly French name originates from his Waloon ancestors, who had left Belgium in the latter part the 17th century for religious reasons. Anton’s father was a well-to do physician with a strong interest in plants. In those days physicians were often botanists, because the depended heavily on herbs to treat diseases. The elder De Bary had leased an island in the river Main where he set up his private botanical garden. Here, he taught his son what he knew about botany and encouraged him to join the excursions of naturalists associated with the Senckenberg Institute, who collected specimens in the nearby countryside. Encouraged by his father, Anton de Bary went to medical school in Berlin and received his medical doctorate Dr. med in March 1853, at the age of 22, although his dissertation title was a botanic subject “De plantarum generatione sexuali”.

Two days before he received his medical doctorate, De Bary published a book on the fungi that cause rust and smut disease in plants. Quickly, his interest for botany overrode the medical one. He liked to tell that diseases only interested him, until the diagnosis was sure, so after just two month – in the interest of the sick as he added jokingly – he gave up the medical profession and became Privatdozent for Botany at the medical faculty of the University of Tubingen in December 1853.

Two years later – not yet 25 years old – he accepted a position at the small university of Freiburg, where he married Antoine Einert, with whom he had four children. After a five-year stopover in Halle, de Bary succeeded the position of Professor Diederich Franz Leonhard von Schlechtendal at the University of Halle in 1867. As editor of the botanical journal Botanische Zeitung, he exercised great influence upon the development of botany. Finally in 1872, he became a professor for botany at the newly founded University of Strasbourg.

What causes plant diseases? De Bary’s work on wheat rust and potato blight.

Drawing of the potato blight pathogen in Die gegenwärtig herrschende Kartoffelkrankheit, ihre Ursache und ihre Verhütung (1861).

Drawing of the potato blight pathogen in Die gegenwärtig herrschende Kartoffelkrankheit, ihre Ursache und ihre Verhütung (1861).

De Bary’s major scientiftic achievement was that “he brought clarity to the study of fungi and fungal diseases in plants,”1. At his time, the origin of plant diseases was not known. A lot of crude theories lingered around: Microbes were considered to arise spontaneously on diseased or dead plant tissue and plant diseases were believed to be caused by either “the little people”, the devil (to mock people), God (to punish people), static electricity in the air or the weather (Since people became sick when the weather became cold and wet, why wouldn’t potato plants become sick?).

De Bary dismantled a lot of this shoddy science. First, he demonstrated that the spores of Puccinia graminis – the causal agent of wheat rust – were formed from fungal mycelium and not by spontaneous generation. Later, he combined thorough experimentation with microscopic observation to unravel the complicated life cycle of the wheat rust fungus. You may recall from the MEMF article on wheat rust that rust fungi produce not only one type of spores, but five different ones. Some of these spores are not able to cause infection of wheat. De Bary took into account the presence of an alternative host – the barberry plant – and carefully tested which spores could infect which plant by inoculating wheat and barberry plants with the uredospores, teliospores, basidiospores, spermatia and aeciospores.

During De Bary’s childhood, the potato blight disease – that caused the Irish potato famine – occurred in Germany too, but not so destructively. Following his work on the rust life cycle, De Bary in 1860 turned his attention to the potato blight pathogen. Again, he connected the dots of valid preexisting ideas by careful experimentation. He was the first to observe the swimming spores of Phytophthora emerge from their sporangia and penetrate leaves. Soon, he succeeded in infecting healthy potato plants with sporangia taken from diseased leaves. 15 years earlier, Reverend Miles Berkeley had published the revolutionary insight that the potato blight disease was “the consequence of the presence of the mould, and not the mould of the decay…”, but while his work was based on observation, De Bary demonstrated experimentally cause and effect.

De Bary laid the foundation for the study of plant diseases worldwide

Anton de Bary surrounded by students in Strassburg (before 1888).

The scope of De Bary’s work is astonishing. His textbook “Morphologie und Physiologie der Pilze”, published in 1866, marked the beginning of the modern study of fungi. Besides his work on fungal life cycles, De Bary asserted that blue-green algae were bacteria (they are known as cyanobacteria today), demonstrated that yeast are fungi, and coined the term “symbiosis” for “the living together of unlike organisms”. As a teacher, he encouraged his students to exact observation and independent, critical thinking – especially of themselves. “You can’t avoid mistakes during the observation, but you have to know them”, he said. Instead of giving his students a formulated topic, he gave them an object and let them find the study question themselves, because “the right question is already half the work”. He attracted and inspired scientist from all over the world and through his former students (Mikhail Woronin from Russia, William Farlow and Marshall Ward from the US and Schimoyama from Japan) established the study of plant diseases in the many countries.

De Bary died of a tumor of the jaw on January 19, 1888 in Strasburg.

 

Sources:

James G. Horsfall 7 Stephen Wilhelm, Heinrich Anton de Bary: Nach einhundertfuenfizg Jahren, Ann. Rev. Phytopathol., 1982

Ludwig Jost, Zum hundersten Geburtstag Anton de Barys. Lebenswerk eines Botanikers des 19. Jahrhunderts. Jena. Verlag von Gustav Fischer, 1930

1 Nicholas P. Money. The Triumph of the Fungi. A rotten history. Oxford University Press. 2006

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The Irish Potato Famine Pathogen

The first MEMF post of 2015 is dedicated to the potato destoryer: Phytophthora infestans  (phyto = plant, phthora = destroyer) – causal agent of the Irish potato famine.

For me, the past two weeks – from Christmas Eve to New Years – have been a gigantic food parade with roasts, dumplings, cakes and Christmas cookies marching by in endless rows. Hunger is very far away from me these days. And yet, less than 200 years ago Europe was struck with one of its worst famines.

Late Blight disease of potatoes

During the Irish potato famine more than 1 million people died and almost 2 million emigrated from Ireland in a period of just five years. The famine was brought about by two year of potato crop failure due to Late Blight disease caused by the oomycete Phytophthora infestans (pronounced fy-TOF-thor-uh in-FEST-ans). What on earth is an oomycete?, you might wonder now. An oomycete is a microbe, which at first sight resembles a fungus with its filamentous growth and spore production. But oomycetes differ from fungi in many aspects: their cell walls are made of cellulose (like plants and algae) and not chitin (like fungi) and the oomycete spores, called zoospores, can swim. The swimming zoospores are the reason why Late Blight disease becomes epidemic during prolonged wet and cold periods.

The first symptoms of Late Blight disease are small black/brown lesions on potato leaves and stems that appear water-soaked. These lesions soon expand and become necrotic. In humid conditions, Phytophthora produces sporangia that are visible as white growth at the edge of the lesions on the lower leaf surface. Sporangia can be dispersed by air or splashed by raindrops, but generally do not survive long-distance travel. When the temperature drops below 15 °C, the Phytophthora sporangia produce the swimming zoospores that spread infection by moving through water on the potato surface and waterlogged soil to infect plants and tubers. Shallow, brownish or purplish lesions appear on the tuber surface after infection. Secondary infections with other microbes subsequently reduce the tuber to a stinking, rotten potato soup.

The Irish potato famine – starving in the midst of plenty

The European weather in September 1845 was unusually cool and wet and allowed easy distribution of the Late Blight pathogen, which can destroy a potato field in less than two weeks. The disease struck again in the following year, leaving the potatoes rotting in the ground and obliterating the primary food source for millions. All over Europe, the potato yield losses led to the “hungry ‘40s”, but no country was hit as hard as Ireland.

The reason for this was demographics. In Ireland, English lords leased their land to English middlemen, who divided the land in small parcel and rented them to Irish tenants. The tenants paid the high rent in the form of produce: grains and sometimes pigs. To fill their own stomachs, they depended entirely on potatoes. When the potato crop failed in 1845 and 1846, the poor tenants were left with nothing to eat.

Between 1845 and 1860 more than 1 million people died of starvation or disease. The worst thing was that Ireland was perfectly able of producing large quantities of food during these years. Only a single crop – the potato – had failed.

Most tenants continued to grow other crops, but they were caught in an impossible bid – they had to sell these crops to pay their rent or face eviction. While people were starving and dying, Ireland continued to export food virtually unabated.

The dramatist George Bernard Shaw refers to the years of suffering in his play, Man and Superman (1903):

VIOLET. The Famine? 

MALONE [with smouldering passion] No, the starvation. When a country is full o food, and exporting it, there can be no famine. Me father was starved dead; and I was starved out to America in me mother’s arms. English rule drove me and mine out of Ireland.

Private charities and religious organisations like the Society of Friends, or Quakers, from America, tried to provide food, mostly flour, rice, biscuits and set up soup kitchens, which were the most successful relief measure of all, but were to few to stop the hunger.

The Choctaw Donation

The most memorable gift to the Irish tenants was a donation of $170- the equivalent of about $5000 today – by the Choctaw tribe of American Indians in 1847. They had a special affinity with the hungry and those who had lost their homes, since it was only 16 years since their tribe had been made homeless and walked the “Trail of Tears” from Oklahoma to Mississippi, along which many of them died. The amount was small, but this extraordinary gift from a people who were themselves terribly impoverished has never been forgotten.

Emigration to America on the ‘coffin ships’

Many of the starving Irish tried to escape to other countries. Around 2 million people left Ireland – mostly to the east coast of the United States. Ireland has never recovered from this demographic watershed and remains the only country in Europe with a smaller population today than it had in 1840.

The emigrants were regarded as the lucky few, but the journey on the overcrowded ships was dangerous and so many people died that the migration ships were called ‘coffin ships’. In the US, the Irish immigrants were not welcomed with open arms. Cartoons soon circled around that depicted the Irish as brutish, simian, bellicose and always drunk. The immigrants took whatever unskilled jobs they could find, working on the docks, pushing carts, or digging canals and labouring on the railroads. Their lives were hard, mortality rates remained high and many of them turned to crime out of boredom, desperation and anger, which only exacerbated the public perception of them as troublemakers and public scourges. It took many years before the Irish immigrants were fully integrated in the US society and the great-grandson of a farmer from County Wexford, who had left Ireland in 1849, became the 35th President of the United States: John F. Kennedy.

 

Sources:

http://botit.botany.wisc.edu/toms_fungi/m2001alt.html, http://www.britannica.com/EBchecked/topic/294137/Irish-Potato-Famine, http://www.dochara.com/the-irish/food-history/the-irish-potato-famine-1846-1850/, http://immigrationinamerica.org/528-great-irish-famine.html