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

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

''Puccinia graminis'', which causes significant disease in cereal 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 represe ...

barley Barley (''Hordeum vulgare''), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains, particularly in Eurasia as early as 10,000 years ago. Globally 70% of barley p ...

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 Prof. K.C. Mehta. Since the 1950s, wheat strains bred to be resistant to stem rust have become available. Fungicides effective against stem rust are available as well. In 1999 a new 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 Ug99 is a lineage of wheat stem rust (''Puccinia graminis'' f. sp. ''tritici''), which is present in wheat fields in several countries in Africa and the Middle East and is predicted to spread rapidly through these regions and possibly further afie ...

). 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 patients among a given population within an area in a short period of time. Epidemics of infectious ...

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 in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...

and the

Middle East The Middle East ( ar, الشرق الأوسط, ISO 233: ) is a geopolitical region commonly encompassing Arabia (including the Arabian Peninsula and Bahrain), Asia Minor (Asian part of Turkey except Hatay Province), East Thrace (Europ ...

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

food security Food security speaks to the availability of food in a country (or geography) and the ability of individuals within that country (geography) to access, afford, and source adequate foodstuffs. According to the United Nations' Committee on World ...

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

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in 2016, suggesting that the disease is returning to Europe. Comprehensive genomic 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 of stem rust

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

Oregon State University Oregon State University (OSU) is a public land-grant, research university in Corvallis, Oregon. OSU offers more than 200 undergraduate-degree programs along with a variety of graduate and doctoral degrees. It has the 10th largest engineering c ...

, "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 (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of ph ...

's time (384–322 B.C). 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,

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan area ...

. 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 Giuseppe Maria Giovene (23 January 1753 – 2 January 1837) was an Italian archpriest, naturalist, agronomist, geologist, meteorologist, entomologist and ichthyologist. elogio-storico, pag. 9, note 8 He is best known for his studies on the "nit ...

(1753–1837), in his work ''Lettera al dottor Cosimo Moschettini sulla ruggine'', 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 18 ...

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 fou ...

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 {{About, , the linguistics term dealing with languages unrelated to any other language in the world, Language isolate, other uses, Isolate (disambiguation){{!Isolate Isolates is a term used in developmental psychology and family studies, to describ ...

from

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and

Zimbabwe Zimbabwe (), officially the Republic of Zimbabwe, is a landlocked country located in Southeast Africa, between the Zambezi and Limpopo Rivers, bordered by South Africa to the south, Botswana to the south-west, Zambia to the north, and ...

, 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 as well as ORCID's website and services to look up authors and their bibliographic ...

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 Elsevier's abstract and citation database launched in 2004. Scopus covers nearly 36,377 titles (22,794 active titles and 13,583 inactive titles) from approximately 11,678 publishers, of which 34,346 are peer-reviewed journals in top-l ...

57189640847

''Sr27''

''Sr27'' is originally from rye ( 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. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...

chlorotic In botany, chlorosis is a condition in which leaves produce insufficient chlorophyll. As chlorophyll is responsible for the green color of leaves, chlorotic leaves are pale, yellow, or yellow-white. The affected plant has little or no ability to ...

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

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in 1972. Deployment in triticale in

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and

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, 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''

An introgression from a wild wheat '' Aegilops tauschii''

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 s ...

ous to ''Mla'' in

. Confers broad resistance to multiple races including

''Sr35''

''Sr35'' is an introgression 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 Rye (''Secale cereale'') is a grass grown extensively as a grain, a cover crop and a forage crop. It is a member of the wheat tribe (Triticeae) and is closely related to both wheat (''Triticum'') and barley (genus ''Hordeum''). Rye grain is ...

'' 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 ''Aegilops'' is a genus of Eurasian and North American plants in the grass family, Poaceae. They are known generally as goatgrasses.

'', 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 one pair of ( homologous) chromosomes. Most species whose cells have nuclei ( eukaryotes) are diploid, meaning they have two sets of chromosomes, where each set contain ...

by Millet ''et al.'', 2017. ''Sr62'' encodes for a unique

tandem protein kinase A protein kinase is a kinase which selectively modifies other proteins by covalently adding phosphates to them (phosphorylation) as opposed to kinases which modify lipids, carbohydrates, or other molecules. Phosphorylation usually results in a fun ...

which is composed of domains which are common among plants. Yu ''et al.'', 2022

Weaponization

In the 1950s, the

United States Air Force The United States Air Force (USAF) is the Aerial warfare, air military branch, service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part ...

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

Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a List of former transcontinental countries#Since 1700, transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, ...

. If the plan were enacted, Boeing B-29 Superfortress 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 the seed of the grass species '' Oryza sativa'' (Asian rice) or less commonly ''Oryza glaberrima'' (African rice). The name wild rice is usually used for species of the genera '' Zizania'' and '' Porteresia'', both wild and domesticat ...

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

gene donor Gene delivery is the process of introducing foreign genetic material, such as DNA or RNA, into host cells. Gene delivery must reach the genome of the host cell to induce gene expression. Successful gene delivery requires the foreign gene delive ...

could be the future.

References

External links

Borlaug Global Rust InitiativeFAOAnimation of stem rust life cycle
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