Stem rust, also known as cereal rust, black rust, red rust or red dust, is caused by the

fungus A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...

''Puccinia graminis'', which causes significant disease in

cereal A cereal is a grass cultivated for its edible grain. Cereals are the world's largest crops, and are therefore staple foods. They include rice, wheat, rye, oats, barley, millet, and maize ( Corn). Edible grains from other plant families, ...

crops. Crop species that are affected by the disease include

bread wheat Common wheat (''Triticum aestivum''), also known as bread wheat, is a cultivated wheat species. About 95% of wheat produced worldwide is common wheat; it is the most widely grown of all crops and the cereal with the highest monetary yield. Ta ...

durum wheat Durum wheat (), also called pasta wheat or macaroni wheat (''Triticum durum'' or ''Triticum turgidum'' subsp. ''durum''), is a tetraploid species of wheat. It is the second most cultivated species of wheat after common wheat, although it repres ...

barley Barley (), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains; it was domesticated in the Fertile Crescent around 9000 BC, giving it nonshattering spikele ...

and

triticale Triticale (; × ''Triticosecale'') is a hybrid of wheat (''Triticum'') and rye (''Secale'') first bred in laboratories during the late 19th century in Scotland and Germany. Commercially available triticale is almost always a second-generation ...

. These diseases have affected cereal farming throughout history. The annual recurrence of stem rust of wheat in North Indian plains was discovered by K. C. Mehta. Since the 1950s, wheat strains bred to be resistant to stem rust have become available.

Fungicide Fungicides are pesticides used to kill parasitic fungi or their spores. Fungi can cause serious damage in agriculture, resulting in losses of yield and quality. Fungicides are used both in agriculture and to fight fungal infections in animals, ...

s effective against stem rust are available as well. In 1999 a new, more virulent race of stem rust was identified against which most current wheat strains show no resistance. The race was named TTKSK (e.g. isolate Ug99). An

epidemic An epidemic (from Greek ἐπί ''epi'' "upon or above" and δῆμος ''demos'' "people") is the rapid spread of disease to a large number of hosts in a given population within a short period of time. For example, in meningococcal infection ...

of stem rust on wheat caused by race TTKSK spread across

Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...

Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

and the

Middle East The Middle East (term originally coined in English language) is a geopolitical region encompassing the Arabian Peninsula, the Levant, Turkey, Egypt, Iran, and Iraq. The term came into widespread usage by the United Kingdom and western Eur ...

, causing major concern due to the large numbers of people dependent on wheat for sustenance, thus threatening global

food security Food security is the state of having reliable access to a sufficient quantity of affordable, healthy Human food, food. The availability of food for people of any class, gender, ethnicity, or religion is another element of food protection. Simila ...

. An outbreak of another virulent race of stem rust, TTTTF, took place in

Sicily Sicily (Italian language, Italian and ), officially the Sicilian Region (), is an island in the central Mediterranean Sea, south of the Italian Peninsula in continental Europe and is one of the 20 regions of Italy, regions of Italy. With 4. ...

in 2016, suggesting that the disease is returning to Europe. Comprehensive

genomic Genomics is an interdisciplinary field of molecular biology focusing on the structure, function, evolution, mapping, and editing of genomes. A genome is an organism's complete set of DNA, including all of its genes as well as its hierarchical, ...

analysis of ''Puccinia graminis'', combined with plant pathology and climate data, has pointed out the potential of the re-emergence of stem wheat rust in UK.

History

The fungal ancestors of stem rust have infected grasses for millions of years and wheat crops for as long as they have been grown.Kaplan, Karen (July 22, 2009) "A red alert for wheat". ''

LA Times The ''Los Angeles Times'' is an American daily newspaper that began publishing in Los Angeles, California, in 1881. Based in the Greater Los Angeles city of El Segundo since 2018, it is the sixth-largest newspaper in the U.S. and the large ...

'' According to Jim Peterson, professor of wheat breeding and genetics at

Oregon State University Oregon State University (OSU) is a Public university, public Land-grant university, land-grant research university in Corvallis, Oregon, United States. OSU offers more than 200 undergraduate degree programs and a variety of graduate and doctor ...

, "Stem rust destroyed more than 20% of U.S. wheat crops several times between 1917 and 1935, and losses reached 9% twice in the 1950s," with the last U.S. outbreak in 1962 destroying 5.2% of the crop. Stem rust has been an ongoing problem dating back to

Aristotle Aristotle (; 384–322 BC) was an Ancient Greek philosophy, Ancient Greek philosopher and polymath. His writings cover a broad range of subjects spanning the natural sciences, philosophy, linguistics, economics, politics, psychology, a ...

's time (384–322 BC). An early ancient practice by the Romans was one where they would sacrifice red animals, such as foxes, dogs, and cows, to Robigus (''fem.'' Robigo), the rust god. They would perform this ritual in the spring during a festival known as the Robigalia in hopes of the wheat crop being spared from the destruction caused by the rust. Weather records from that time have been reexamined and it has been speculated that the fall of the Roman Empire was due to a string of rainy seasons in which the rust would have been more harsh, resulting in reduced wheat harvests. Laws banning barberry were established in 1660 in

Rouen Rouen (, ; or ) is a city on the River Seine, in northwestern France. It is in the prefecture of Regions of France, region of Normandy (administrative region), Normandy and the Departments of France, department of Seine-Maritime. Formerly one ...

, France. This was due to the fact that European farmers noticed a correlation between barberry and stem rust epidemics in wheat. The law banned the planting of barberry near wheat fields and was the first of its kind. The parasitic nature of stem rust was discovered in the 1700s. Two Italian scientists, Fontana and Tozzetti, first explained the stem rust fungus in wheat in 1767. Italian scientist Giuseppe Maria Giovene (1753–1837), in his work , also thoroughly studied the stem rust. Thirty years later it received its name, ''Puccinia graminis'', by Persoon, and in 1854 brothers Louis René and

Charles Tulasne Charles Tulasne (5 September 1816 – 28 August 1884) was a French physician, mycologist and illustrator born in Langeais in the département of Indre-et-Loire. He received his medical doctorate in 1840 and practiced medicine in Paris until 185 ...

discovered the characteristic five-spore stage that is known in some stem rust species. The brothers were also able to make a connection between the red (urediniospore) and black (teliospore) spores as different stages within the life cycle of the same organism, but the rest of the stages remained unknown.

Anton de Bary Heinrich Anton de Bary (26 January 183119 January 1888) was a German surgeon, botanist, microbiologist, and mycologist (fungal systematics and physiology). He is considered a founding father of plant pathology (phytopathology) as well as the foun ...

later conducted experiments to observe the beliefs of European farmers regarding the relationship between the rust and barberry plants, and after connecting the basidiospores of the basidia stage to barberry, he also identified that the aeciospores in the aecia stage reinfect the wheat host. Upon de Bary's discovery of all five spore stages and their need for barberry as a host, John Craigie, a Canadian pathologist, identified the function of the

spermogonium {{Short pages monitor

''Sr9h''

Discovered and found to provide Ug99 resistance by Rouse ''et al.'', 2014. However Ug99 isolates from

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

and

Zimbabwe file:Zimbabwe, relief map.jpg, upright=1.22, Zimbabwe, relief map Zimbabwe, officially the Republic of Zimbabwe, is a landlocked country in Southeast Africa, between the Zambezi and Limpopo Rivers, bordered by South Africa to the south, Bots ...

, both in 2010, already had virulence when retested against this new gene. Both Rouse and Wessels ''et al.'', 2019 find the Ug99 resistance of cv. 'Matlabas' is probably due to this gene. Wessels finds it is present in less than 5% of breeding lines.

''Sr14''

''Sr14'' does not protect seedlings against TTKSK SB

ORCID The ORCID (; Open Researcher and Contributor ID) is a nonproprietary alphanumeric code to uniquely identify authors and contributors of scholarly communication. This addresses the problem that a particular author's contributions to the scien ...

0000-0002-4091-2608
but does provide moderate resistance at later stages. It is effective against TTKST.

''Sr22''

There is considerable variation among ''Sr22'' alleles, with some conferring resistance and some susceptibility. MAMH

0000-0002-8952-5684

Scopus Scopus is a scientific abstract and citation database, launched by the academic publisher Elsevier as a competitor to older Web of Science in 2004. The ensuing competition between the two databases has been characterized as "intense" and is c ...

57189640847

''Sr27''

''Sr27'' is originally from

rye Rye (''Secale cereale'') is a grass grown extensively as a grain, a cover crop and a forage crop. It is grown principally in an area from Eastern and Northern Europe into Russia. It is much more tolerant of cold weather and poor soil than o ...

( Imperial Rye), now () widely found in

and rarely in hexaploid wheat. Located on the 3A chromosome arm, originally from 3R. Virulence has been observed in field '' Pgs'' and in an artificial ''Pgt'' ''Pgs''. When successful, ''Sr27'' is among the few ''Sr''s that does not allow the underdeveloped uredinia and slight degree of sporulation commonly allowed by most ''Sr''s. Instead there are

necrotic Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. The term "necrosis" came about in the mid-19th century and is commonly attributed to German pathologist Rudolf Virchow, who is ...

or chlorotic flecks. ''Pgt'' virulent on wheat with this gene was found in

Kenya Kenya, officially the Republic of Kenya, is a country located in East Africa. With an estimated population of more than 52.4 million as of mid-2024, Kenya is the 27th-most-populous country in the world and the 7th most populous in Africa. ...

in 1972. Deployment in triticale in

New South Wales New South Wales (commonly abbreviated as NSW) is a States and territories of Australia, state on the Eastern states of Australia, east coast of :Australia. It borders Queensland to the north, Victoria (state), Victoria to the south, and South ...

and

Queensland Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...

, Australia, rapidly produced virulence between 1982 and 1984 – the first virulence on this gene in the world. (This was especially associated with the cultivar Coorong.) Therefore, CIMMYT's triticale offerings were tested and many were found to depend solely on ''Sr27''. Four years later, in 1988, virulence was found in

. ''Sr27'' has become less common in CIMMYT triticales since the mid-'80s.

''Sr31''

Ug99 is virulent against ''Sr31'', which was effective against all previous stem rust races.

''Sr33''

introgression Introgression, also known as introgressive hybridization, in genetics is the transfer of genetic material from one species into the gene pool of another by the repeated backcrossing of an interspecific hybrid with one of its parent species. Introg ...

from a wild wheat ''

Aegilops tauschii ''Aegilops tauschii'', the Tausch's goatgrass or rough-spike hard grass, is an annual grass species. It is native to Crimea, the Caucasus region, western and Central Asia, Afghanistan, Pakistan, the western Himalaya, and parts of China, and has b ...

ortholog Sequence homology is the biological homology between DNA, RNA, or protein sequences, defined in terms of shared ancestry in the evolutionary history of life. Two segments of DNA can have shared ancestry because of three phenomena: either a speci ...

ous to ''Mla'' in

. Confers broad resistance to multiple races including Ug99.

''Sr35''

''Sr35'' is an

from '' Triticum monococcum'' conferring some resistance. ''AvrSr35'' – a ''Pgt'' gene so named because it was discovered causing avirulence on ''Sr35'' – is the ancestral allele to all ''Pgt'' alleles that are virulent on ''Sr35''. ''AvrSr35'' came first, followed by the selective pressure of widespread adoption of ''Sr35'' wheat races, followed by the evolution of virulence on ''Sr35'' by way of nonfunctionalization mutations of ''AvrSr35''.

''Sr59''

Recently, a new stem rust resistance gene ''Sr59'' from '' Secale cereale'' was introgressed into wheat, which provides an additional asset for wheat improvement to mitigate yield losses caused by stem rust.

''Sr62''

An NLR (or NB-LRR, or

R gene Resistance genes (R-Genes) are genes in plant genomes that convey plant disease resistance against pathogens by producing R proteins. The main class of R-genes consist of a nucleotide binding domain (NB) and a leucine rich repeat (LRR) dom ...

) from '' Aegilops sharonensis'', one of only three resistance genes from that species. Was discovered by Yu ''et al.'', 2017 and then introgressed into

hexaploid Polyploidy is a condition in which the cells of an organism have more than two paired sets of ( homologous) chromosomes. Most species whose cells have nuclei (eukaryotes) are diploid, meaning they have two complete sets of chromosomes, one fro ...

by Millet ''et al.'', 2017. ''Sr62'' encodes for a unique tandem protein kinase which is composed of domains which are common among plants. Yu ''et al.'', 2022

''SrTmp''

Originally from the widespread Ethiopian ''. Resistant to Ug99, susceptible to .

Weaponization

In the 1950s, the

United States Air Force The United States Air Force (USAF) is the Air force, air service branch of the United States Department of Defense. It is one of the six United States Armed Forces and one of the eight uniformed services of the United States. Tracing its ori ...

developed Operation Steelyard, a plan to drop wheat stem rust mixed with feathers over wheat farms in the

Soviet Union The Union of Soviet Socialist Republics. (USSR), commonly known as the Soviet Union, was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 until Dissolution of the Soviet ...

. If the plan were enacted,

Boeing B-29 Superfortress The Boeing B-29 Superfortress is a retired American four-engined propeller-driven heavy bomber, designed by Boeing and flown primarily by the United States during World War II and the Korean War. Named in allusion to its predecessor, the Bo ...

bombers would drop 500-pound M115 bombs over Soviet farms, with the intention of destroying up to 50% of the Soviet winter wheat harvest.

Future

Alone amongst cereals,

rice Rice is a cereal grain and in its Domestication, domesticated form is the staple food of over half of the world's population, particularly in Asia and Africa. Rice is the seed of the grass species ''Oryza sativa'' (Asian rice)—or, much l ...

is naturally immune to rusts. If a genetic source of this resistance could be identified, transgenic wheats with rice as the gene donor could be the future.

References

External links

Borlaug Global Rust InitiativeStem rust
by FAO (the

Food and Agriculture Organization The Food and Agriculture Organization of the United Nations; . (FAO) is a specialized agency of the United Nations that leads international efforts to defeat hunger and improve nutrition and food security. Its Latin motto, , translates ...

of the United Nations
Animation of stem rust life cycle
* * {{Taxonbar, from=Q1342327 Cereal diseases Puccinia Fungi described in 1794