Tag Archives: Norman Borlaug

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.


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.


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.


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.”


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.