Author Archives: Sarah

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

The evil chocolate sisters – Frosty Pod and Witches Broom

Cacao pod hanging on the Theobroma cacao tree in Indonesia.

Cacao pod hanging on a cacao tree in Indonesia.

Cacao Frosty Pod! Sounds like the name of a new breakfast cereal. Hidden behind this misleading, cheerful name is a nasty disease of cacao plants that – together with its sister species Witches Broom – is destroying cacao plantations in South America and seriously threatening our demand for the most delicious chocolate.

How to make chocolate from cacao trees

Let’s first have a look at the origin of our chocolate. A few years ago, I have been working as a guide in the Palmengarten – Germany’s biggest botanical garden – in Frankfurt/Main. One of my favorite plants to show was Theobroma cacao – the cacao tree. It is surprising how few school kids know that chocolate is not growing as a chocolate bar on a tree.

Chocolate is made from cacao beans that are produced inside massive fleshy pods that stick out from the stem and branches of the evergreen cacao tree. After harvest, the beans are removed from the pods and set in a wooden box for fermentation. During the fermentation process, a soup of yeast and bacteria enhances the chocolate flavor and reduces the bitterness. After drying the fermented beans, grinding and adding milk and sugar, the cacao beans have been promoted to a bitter sweet symphony of chocolate flavors.

cacao_crudo

Cacao beans in a chocolate shop in Mexico.

Where is cacao grown?

Cacao is grown in the hot and humid tropical regions around the Equator. Two-third of the world’s cacao is produced in only four West-African countries: Ivory Coast, Ghana, Nigeria and Cameroon. Ivory Coast and Ghana dominate cacao production: together they cultivate half of the world’s cacao. Now you might wonder: If most of the cacao is produced in West-Africa, why should we worry about a fungus attacking the cacao trees in South America?

 

South America is home to the finest chocolate variety

The reason is the following: The cacao grown in West-Africa is mainly the Forastero variety – also called bulk cacao – that is used for manufacturing mass-market chocolate. In South America, the Criollo and Trinitario varieties provide the delicious and delicate “fine grade” cacao beans. Only 5% of the world’s cacao beans are considered “fine grade. Ecuador is the world’s largest producer of “fine grade” beans, followed by Venezuela, Panama and Mexico.

Evil chocolate sister – Witches Broom

In the early 19th century, Ecuador was one of the biggest chocolate suppliers. Over 30% of the world’s cacao was produced in Ecuador allowing the “Cacao kings” living north of the capital of Guayaquil extravagant lifestyles. Their excesses were abruptly ended in 1921 when Witches Broom eradicated the Ecuadorian cacao crop.

Witches Broom refers to a deformity of the leaf-bearing branches and stem-borne cacao flowers, which result in a dense mass of swollen branches tipped with bunches of stunted leaves – the brooms. The stalks that support the cacao pods become thickened and the entire fruit is distorted. Witches Broom is caused by the fungus Moniliophthora perniciosa – a mushroom-forming fungus. Mushrooms are the sexual fruiting bodies of this class of fungi. The mushrooms appear on the cacao broom when it has dried out and they produce millions of basidiospores that are blown by the wind to neighboring cacao trees.

Frosty pod rot of cacao caused by M. roreri with whitish to creamy-colored spores on the pod surface. Image from Plant Health Progress article: The Impact of Plant Diseases on World Chocolate Production

Frosty pod rot of cacao caused by M. roreri with whitish to creamy-colored spores on the pod surface.
Image from Plant Health Progress article:
The Impact of Plant Diseases on World Chocolate Production

Frosty Pod – the really evil chocolate sister

Frosty Pod Disease is caused by the Witches Broom’s sister species – Moniliophthora roreri. Frosty Pod is like a crippled, but more aggressive version of Witches Broom. No mushroom formation or any other sexual fruiting body has ever been observed for the Frosty Pod fungus.

(Maybe it’s the lack of sex that explains its crave for chocolate.). It is named after a layer of white mycelium that develops on dark, chocolate-colored spots on the cacao pods. These dark spots appear 40-80 days after the fungal spores has germinated on the pod and penetrated the pod epidermis. During this asymptomatic stage, Frosty Pod causes internal damage to the pod and beans. One week after the appearance of the dark spots, the characteristic white powder appears on the pod surface. After ca. three month, the fruits become dry and remain mummified on the cacao trees trunk, where they serve as mass producers of spores (over 7 billion per fruit!) that cause waves of infection over a long period of time.

Frosty Pod Rot is found in all north-western countries in South America. It is more destructive than black pod (a cacao disease in West Africa) and more dangerous and difficult to control than witches broom. In affected countries from Panama to Mexico the yield losses can be higher than 80% and Frosty Pod is the main yield-limiting factor.

Sources: Aime et al. , Mycologica, 2005,  International Cacao Industry (http://www.icco.org/about-cocoa/pest-a-diseases.html), Makechocolatefair.org, “Cacao Diseases: Important Threats to Chocolate Production Worldwide” Myths and Misnomers, Harry C. Evans, CAB International, Egham, Surrey, UK

Coffee rust or Why the British drink Tea instead of Coffee.

© Sarah Maria Schmidt

© Sarah Maria Schmidt

There is not a single morning that I do not start with a cup of coffee. Without caffeine, my brain and body refuse to function. To ensure a thorough supply with coffee throughout the day, I have one espresso machine at home, another at work and a filter coffee machine for guests. I am sharing my passion (and dependency) for coffee with the coffee rust fungus Hemileia vastatrix – an iconic pathogen that made the British drink tea instead of coffee.

(Very) Brief history of coffee culture and trade

Let’s go back in time.

In the early days, coffee was mainly used as medicine and food additive by North African tribes. Around the early 1500s, the Turkish and Arabians had got the hang of it and enjoyed their coffee in socially amiable coffeehouses. By the early 17th century, Europeans got hooked on coffee. Coffeehouses had sprung up in all major cities of Europe and had become popular places to meet, enjoy coffee and discuss philosophy, religion, and politics.

Some smart Dutch businessmen saw their opportunity and began to invest in and trade coffee. They grew coffee in their colonies beginning in Ceylon in 1658. In 1796, control of Ceylon was handed over to the British and British colonials began to clear the Ceylon rain forest to establish coffee plantations. By the 1870s, Ceylon’s plantations were exporting nearly 100 million pounds of coffee a year, most of it to England. For a few decades, Ceylon was the world’s top coffee producer.

Coffee Berries and Flower. © Sarah Maria Schmidt

Coffee Berries and Flower. © Sarah Maria Schmidt

The coffee rust fungus – a perfect parasite

In 1869, the coffee rust fungus Hemileia vastatrix (named for the unusual shape of its spores: smooth on one side, roughened on the other) entered the stage in Ceylon. Coffee rust infections occur on the coffee leaves. The first symptoms are small, pale yellow spots on the upper leaf surface. As these spots grow, masses of orange uredospores (~400.000 per spot) appear on the leave undersurface. The spores germinate on the humid leaf surface and the fungus enters the plant tissue through natural openings. Inside the leaf, the rust fungus forms an intimate connection with the coffee plant by growing a feeding structure – called haustorium – within the living plant cell. Via the haustorium, the rust fungus absorbs its food from the coffee plant – without killing its host. When all the nutrients are sucked out, the infected leaves prematurely fall off and eventually the tree dies, often before it can produce coffee berries. The fallen leaves are still full of fungal spores.Rust fungi produce spores in huge amounts. One orange spot contains more than 400.000 uredospores. This means that a single, heavily infected coffee plant can produce millions of infectious spores, which are blown by the wind to other coffee plants.

Coffee Rust. © Sarah Maria Schmidt

Coffee Rust. © Sarah Maria Schmidt

Coffee rust turned Ceylon into a country of tea growers

After Hemileia’s arrival on Ceylon, annual coffee harvests in Ceylon plummeted. Many coffee growers were ruined. Former coffee plantations were left to rot. A few far-sighted growers recognized that the plantations could be turned over to tea-growing. One of them was the Scotsman Thomas Lipton, who purchased five ex-coffee plantations in 1890 to grow tea, which he sold in his grocery chains. He was the first to sell tea in boxed small quantities to make it available for everyone. Ever since the raging of coffee rust, Ceylon is known as the exporter of the world’s finest teas.

Tea that the British like to enjoy in the morning, afternoon and evening. Instead of a delicious cup of coffee! 1

 

1 Some people claim that it was not coffee rust, but the bad quality of the Ceylon coffee that turned the English into tea drinker.

Sources: http://www.apsnet.org/edcenter/intropp/lessons/fungi/Basidiomycetes/Pages/CoffeeRust.aspx; The Triumph of the Fungi. A rotten history. Nicholas P. Money. Oxford University Press. 2007.

 

My parents have a glass of freshly squeezed orange juice every morning. They believe in its health benefits. My mom claims that she did not have a cold ever since they started their day with a glass of fresh orange juice. They buy huge boxes of oranges every week at the local market.

A few weeks ago they stopped. The oranges were too expensive.

A disease called Citrus Greening – also known as Huanglongbing (HLB) or yellow dragon disease – next to environmental effects (drought in Brazil, hurricanes in Florida, dry summer in Spain) – diminishes our oranges and spurs the prices. Named for its small, partially green fruits, Citrus Greening has ravaged orange fields in Florida and the US East Coast. Infected trees produce misshapen fruits with bitter juice and dark aborted seeds that drop prematurely. Eventually the tree stops bearing fruits and dies.

Misshapen, green orange fruits from a Citrus Greening – infected tree.

Citrus Greening is transmitted by a tiny mottled brown insect – the Asian Citrus Psyllid (Diaphorina citri). The psyllid feeds on the stems and leaves of citrus plants. Not limited to orange trees, it also feasts on grapefruits, pomelos, mandarins, lemons and lime. While it feeds, it damages the young citrus leaves. But that is not what it makes it so nasty.

The nasty thing about the Asian Citrus Psyllid is that it can take up a bacterium in its body and transmit it to the next citrus plant it feeds upon. This Huanglongbing (HLB) bacterium can kill a citrus tree in as little as five years and there is no known cure and no resistant citrus plant.

Asian Citrus Psyllid.

Both the Asian Citrus Psyllid and the HLB bacterium originate from Asia or India and then spread to other parts of the world where citrus is grown and where they have no natural enemies. The Asian Citrus Psyllid – and with it the HLB bacterium – can easily move by wind from one citrus-growing area to another.

Researchers in Florida, Brazil and California are working hard on breeding HLB-resistant citrus trees and developing chemical controls with insecticides. Insecticides however have the disadvantage that they are also toxic to honey bees.

The most promising weapon against the Asian Citrus Psyllid is its natural enemy – the parasitic wasp Tamarixia radiata. Females of this tiny wasp – not bigger than the dot at the end of this sentence – lay their eggs underneath the psyllid nymphs, and after hatching, the parasitoid larvae attack and kill the psyllid.

Sounds brutal? Might save our orange juice!

 

Sources:

http://www.crec.ifas.ufl.edu/extension/greening/index.shtml

http://www.saveourcitrus.org/index.php/what-are-the-diseases

http://californiacitrusthreat.org/huanglongbing-citrus-greening.php

“Asian Citrus Pyllid and Hanglongbing Disease”. UC Davis. August 2013

Pictures: Wikipedia

Cereal Killer: Stem Rust Threatens World Wheat Supply

Wheat stem rust (Puccinia graminis f. sp. tritici) has caused devastating epidemics of wheat in the history of mankind. It can destroy entire wheat harvests – leaving nothing but black stems and shrivelled grains. Currently, a new variety, Ug99, is spreading from Africa towards Central and South Asia, where 20% of the world’s wheat is produced.

Last MEMF blog’s entry was about Norman Borlaug, who saved millions of lives by developing high-yielding and stem-rust resistant wheat cultivars that spurred the Green Revolution. This blog will focus on the pathogen that he was fighting: stem rust.

wheat_stem_rust

Stem rust plagues wheat and threatens our daily bread

Stem rust is such a devastating disease, because it attacks the crop that is most intimately connected with human civilization: wheat. Without the cultivation of cereals by hunter-gatherers in the Fertile Crescent, there would have been no civilization. Today, wheat is cultivated on 25% of the global arable land. After rice, it is the second most important grain crop of the world and accounts for one fifth of humanity’s calorie intake (rice has a similar share, all other foods combined account for the rest). From South Asia through to Central Asia across the Middle East and on to North Africa, wheat is a staple food (meaning the main dietary component). Can you imagine the Italians without pasta, North Africans without couscous, Indians without Chapatis or the Lederhosen-wearing inhabitants of Bavaria without Weissbier?

Next to these traditional wheat-eating (and drinking) regions, some 40 million tons of wheat are imported every year to Sub-Saharan countries. Wheat used to be a minor crop there, but nowadays it is important crop for Sub-Saharan food security.

The over-complicated life cycle of stem rust fungi

The first symptoms of stem rust are beautiful -from my very personal point of view. Bright-orange, “rusty” pustules occur on the wheat leaf surface and stems containing up to 350.000 urediniospores. Urediniospores are asexual spores. Asexual means that the spores are genetically identical clones of one another. If the conditions are favourable (Stem rust likes it hot and humid.), the fungus produces so many urediniospores that they form huge orange clouds above the fields and quickly infect every single plant. The spores are dispersed by the wind and can infect wheat plants that are grown thousands of miles away.

Currently, this asexual life cycle (read: No Sex!) of stem rust is the most important. This is due to large-scale eradication of a horny bush named barberry. Wondering what barberry has to do with a disease of wheat?

This question leads us to the complicated life cycle of rust fungi – one of the most complicated ones on earth. If you think that your (sex) life is complicated, you don’t want to be a rust fungus. Next to the clonal urediniospores, stem rust also mates on wheat and produces black teliospores. Teliospores are sexual spores. In other words, they are new varieties emerged from the recombination of their parents’ genetic material. The stem rust’s children, if you want.

Teliospores cannot infect wheat. They infect barberry – as an alternative host. On the barberry plant, the stem rust fungus celebrates a bacchanal, producing at first small clusters of pycnia that excude pycnidiospores a sticky honeydew. The honeydew attracts insects, which will carry the pycnidiospores to other parts of the barberry plant where they mate again and grow through to the lower leave surface to release dikaryotic aeciospores. Like the teliospores, aecsiopores are not able to infect the plant on which they are produced. Instead they are disseminated by wind and rain to young wheat plants and start the infection cycle as new genetic varieties all over again.

barberry7a

Yes, you counted correctly! Stem rust produces four different kinds of spores on two different plants. It took scientists decades to put together the pieces of this complicated lifecycle (If you got lost, there is a cute animation about the rust lifecycle.). Anton de Bary finally succeeded in 1860. The sexual life cycle of stem rust involving the telio -, pycnio- and aeciospores does not play a big role in stem rust infections in Europe and the US. Farmers early on recognized the vicious connection between barberry and stem rust infections leading to large-scale barberry eradication program in Europe and the US in the early 20th century. However, the new variety from Africa, Ug99, might have evolved on a barberry plant.

Rust never sleeps – Ug99 is on a deadly trail towards Europe and Asia

So, what is Ug99?

Ug99 – Ug for its country of origin, 99 for the year it was confirmed – is a highly aggressive strain from Uganda that overcame most wheat resistance genes. It was Norman Borlaug, the Father of the Green Revolution, who had created most of the stem-rust resistant wheat varieties. His masterpiece was a complicated cross-hybridization of a segment from a rye chromosome into wheat. This chromosome segment not only contained resistance genes to stem rust – among them the durable Sr31 gene -, but also genes that increased grain yields. This made the new cultivars quickly popular in the whole world. They were so effective that stem rust declined to almost insignificant levels everywhere by the mid-1990s.

Until Ug99 entered the stage! Ug99 can overcome more wheat resistance genes, including Sr31, than any other stem rust variety before. The fungus changes rapidly by single step mutations and already consists of seven varieties with different virulence patterns. It spreads quickly through Africa and the Arabian Peninsula. In 2004, it spread from Uganda to Kenya, and then to Ethiopia and southern Sudan causing up to 80% yield loss in Kenya and Uganda. In 2007, Ug99 jumped the Red Sea and is now widespread in Yemen and Iran. So far, Ug99 did not arrive in one the major wheat producing countries: China, India, the US and Russia. If it does, our daily bread is threatened: 80-90% of the global wheat cultivars are susceptible to Ug99.

Ug99spread

What do scientists do? Concerted effort – the Borlaug Global Rust Initiative

Norman Borlaug was immediately alarmed when he learned about Ug99. At the age of 91, he took up the fight against stem rust once again. By 2005, he had drummed up an international consortium of scientists from CIMMYT, ICARDA, FAO and the ARS of the US Department of Agriculture – the Borlaug Global Rust Initiative. Coordinated by Cornell University the BGRI concentrated efforts on developing and deploying new effective resistance of wheat stem rust by stacking four or five resistant genes. So far, the researchers produced 60 experimental wheat varieties. The new wheats have only one drawback: lower yield (the opposite of Borlaug’s wheat varieties).

Lower yields make their use unpopular in countries where Ug99 has not yet arrived – including the major wheat producers. Thus, the threat of wheat stem rust prevails! As Borlaug said: “Rust never sleeps.”

wanted-stemrust

Sources: FAOstats; wheat.org; Schumann, G.L. and K.J. Leonard. 2000. Stem rust of wheat (black rust). The Plant Health Instructor. DOI: 10.1094/PHI-I-2000-0721-01. Updated 2011.

Norman Borlaug – the Father of the Green Revolution

Norman Borlaug in Mexico. 1970. LIFE Magazine photo.

Norman Borlaug in Mexico. 1970. LIFE Magazine photo.

Norman Ernest Borlaug (March 25, 1914 – September 12, 2009) was an American plant pathologist, agronomist and Peace Nobel laureate. He revolutionized agriculture by bringing about the Green Revolution – a series of research, development and technology transfer that increased agricultural production worldwide, thereby uplifting over a billion people from poverty and starvation.

Inspired by last week’s nominations for the Nobel prizes, I decided to dedicate the first blog on Microbes Eat My Food to Norman Borlaug – the only phytopathologist who won the Nobel Peace Prize.

Norman Borlaug witnessed the impact of technical innovations as a teenager

Norman Borlaug experienced the impact of agricultural innovations on rural life early on in his life. Born in Saude, Iowa in 1914, he grew up on a small farm. At that time, farming was done the same ways as hundreds of years ago – with sickles, manpower and horses. The Borlaug’s house had no insulation and no running water. With the meagre yield from their cornfields, Norman Borlaug’s family could barely survive.

When Borlaug was fifteen years old, the spread of agricultural technologies changed the farmer’s lot drastically. These technologies included improved crop varieties like hybrid corn, synthetic fertilizer and tractors. At first, they were met with suspicion, scepticism and mistrust, but once implemented, the farmers’ wealth increased and the liberation from the daily animal care allowed them for the first time to pursue personal interests. Norman Borlaug’s interests – besides getting an education – were sports. He was an athlete: playing baseball, wrestling, being captain of the football team.

Norman Borlaug’s career was not straightforward

Sports got him into college. In October 1929, the Wall Street had crashed – catapulting millions of people into unemployment and poverty. When Norman Borlaug graduated from high school in 1931, his family was broke and could not pay for the college tuition fees. Luckily, he was invited to join the college football team at St. Paul’s University in Minnesota. To afford food, rent and tuition, he had to handle three side jobs next to his studies; living on a meal-to-meal basis. As an undergraduate, Borlaug studied Forestry and he would have become a forester, if not Prof. Stakman – a pioneer in wheat rust research –had convinced him to switch to crop plant pathology. Stakman had given a memorable lecture about wheat stem rust titled “These shifty, little enemies that destroy our food crops”. His hands-on methods imprinted Borlaug and his fellow students:

Stem rust on wheat

Stem rust on wheat

Stakman did more than teach to the textbook: he produced cereal caregivers. These self-contained “general practitioners” were capable of diagnosing disease and counteracting it wherever they might be in the world. Much of their skills were learned during his outdoor seminars in which he required all of us to interpret the symptoms of scores of wheat disease and to recommend remedies.1

After his PhD on the flax fungus Fusarium lini, at the age of 27, Norman Borlaug began working for the chemical company E.I. du Pont de Nemours & Company in Philadelphia. He reached Philadelphia with his wife on the day when Pearl Harbour was bombed. Classified as “essential to the war effort”, he was spared from army service, but had to work for the US army by coming up for solutions to war-related problems like the development of camouflage, disinfectants, malaria prevention and insulation of electronic devices. When he was offered a position as plant pathologist in an agricultural research program of the Rockefeller Foundation in Mexico, he quit his secure, well-paid position at Du Pont and moved to Mexico in October 1940. He was 30-years old and eager to put his science to work and lift Mexico’s impoverished farmers out of hunger and poverty.

Norman Borlaug in Mexico –the silent wheat revolution.

Working for the Rockefeller Foundation was not as glamorous as one would imagine. The research station at Chapingo – 25 miles from Mexico City had no greenhouses, no equipment, no technicians, no field hands and no fields – just a crude adobe cabin. During the first years in Mexico, he encountered many obstacles and setbacks. Next to the lack of facilities and trained personnel, he struggled with local bureaucrats, the mistrust of farmers and the lack of support from the Rockefeller Foundation.

Many times during the four years, frustrated by unavailability of machinery and equipment, without the assistance of trained scientists, travelling over bad roads, living in miserable hotels, eating bad food, often sick with diarrhoea and unable to communicate because of lack of command of the language, I was certain I had made a dreadful mistake in resigning from my former position.1

But Norman Borlaug had a vision! And a goal!

He wanted to save Mexico from famines by providing them with the best, highest-yielding and stem-rust resistant wheat.

Single-handedly, he crossed and tested thousands of wheat cultivars; improved the breeding process by shuttling back and force between Chapingo and the 300 miles distant Sonora to catch two growing seasons and set up a training program for Mexican high school boys as wheat breeders and for farmers in good agricultural practices (with flyers reading “Farmers Field Day – Free Beer and Barbecue”).

After 19 years of relentless breeding, research and training he had accomplished his mission. Borlaug had developed novel, high-yielding, stem-rust resistant, semi-dwarf (to avoid collapse of the stem under the heavy weight of the grains) wheat cultivars that made up 95% of the wheat harvest. Mexico was producing more than enough wheat for its need and was free of hunger. Norman Borlaug had accomplished the silent wheat revolution.

Norman Borlaug in India and Pakistan – The Father of the Green Revolution.

Borlaug training scientists.

Borlaug training scientists.

By the 1960ties, Norman Borlaug was no longer a solo fighter in the Mexican desert; he was a sought-after advisor. He had set up a training program for young people from developing countries at his Mexican facility – now grown into the International Maize and Wheat Improvement Center (CIMMYT) and his wheat seeds, along the scientists he trained,  spread around the world.

In the 1960s, scientists from India and Pakistan urged Norman Borlaug to visit the region. Both countries were on the brink of war about Kashmir and the entire subcontinent of South Asia was marked by famines and starvation. India was surviving on large-scale food aid sent by the United States and sold in fair-price shops. Stem rust was plaguing their wheat fields. Borlaug immediately saw the need to modernize agriculture. At first his recommendations were not met well.

When I asked about the need to modernize agriculture, both scientists and administrators typically replied: “Poverty is the farmers’ lot; they are used to it.” I was informed that the farmers were proud of their lowly status, and was assured that they wanted no change. After my own experiences in Iowa and Mexico, I didn’t believe a word of it.1

Norman Borlaug set to work with his characteristic fervour, impatience and occasional lack of tact – despite formidable obstacles. He had to operate in two countries at war, fight rumours about his wheat cultivars poisoning water buffalos and making men sterile and organize seed shipments from Mexico to South Asia that exceeded any amount of seed that had ever been shipped internationally. In 1966, he shipped 14.000 tons of wheat seed to India.

Next to providing his semi-dwarf wheat seeds, he pushed for a reformation of the agricultural policy – including the development of a fertilizer industry, reasonably prized fertilizer, a ban of the cheap food policies that subsidized city folk at the farmer’s expense and a fair price for the harvest. Within eight years, he succeeded: India’s wheat harvest in 1968 surpassed even Norman Borlaug’s own optimistic estimations. Pakistan became self-sufficient in wheat production by 1969 with about 1 million tons surplus of local needs. The higher farmer’s incomes provided extra buying power and an increase in personal spending. Governments were forced to provide public services such as transportation, better schools and better roads thereby resulting in a rising of life standards. 55 years old, Norman Borlaug was the Father of the Green Revolution.

He has often been credited as having saved more lives than any other person. In 1970, Norman Ernest Borlaug received the Peace Nobel Prize for alleviating the world from hunger.

1 “Our Daily Bread. The Essential Norman Borlaug.” Noel Vietmeyer. October 2011.