View source for Wheat leaf rust

{{short description |Fungal disease of wheat, most prevalent}}
{{distinguish |text=''[[Puccinia graminis]]'' which causes "stem or black rust", or ''[[Puccinia striiformis |P. striiformis]]'' which causes "stripe, yellow, or strip rust"}}
{{Infobox plant disease
 |name=Wheat leaf rust
 |image=Wheat_leaf_rust_on_wheat.jpg
 |caption=[[Symptom]]s
 |common_names=Brown rust<br/>
Leaf rust
 |causal_agents=''[[Puccinia triticina]]''
 |hosts=[[wheat]]
 |vectors=
 |EPPO_codes=PUCCRT
 |distribution=Worldwide
}}
{{Speciesbox
 |image=
 |image_caption=
 |genus=Puccinia 
 |species=triticina
 |authority=[[Erikss.]] (1899)
 |synonyms=
*''Puccinia dispersa'' f. sp. ''tritici'' <small>Erikss. & E.Henn. 1894</small>
*''Puccinia recondita'' f. sp. ''tritici'' <small>(Eriks. & E.Henn.) D.M.Henderson </small>
}}

'''Wheat leaf rust''' ('''''Puccinia triticina''''') is a fungal disease that affects [[wheat]], [[barley]], [[rye]] stems, leaves and grains. In [[temperate zones]] it is destructive on [[winter wheat]] because the pathogen [[overwinter]]s. Infections can lead up to 20% [[Crop yield |yield]] loss. The pathogen is a ''[[Puccinia]]'' [[Rust (fungus) |rust fungus]]. It is the most prevalent of all the wheat rust diseases, occurring in most wheat-growing regions.<ref name="Liu-et-al-2013"> {{cite journal |last1=Liu |first1=M |last2=Rodrigue |first2=N. |last3=Kolmer |first3=J. |title=Population divergence in the wheat leaf rust fungus ''Puccinia triticina'' is correlated with wheat evolution |journal=[[Heredity (journal) |Heredity]] |publisher=[[Nature Research]] |volume=112 |issue=4 |date=2013-12-04 |doi=10.1038/hdy.2013.123 |pages=443–453 |pmid=24301080 |pmc=3966128 |s2cid=26583039 |doi-access=free }} </ref> It causes serious [[epidemic]]s in [[North America]], [[Mexico]] and [[South America]] and is a devastating seasonal disease in [[India]]. ''P. triticina'' is [[heteroecious]], requiring two distinct hosts (alternate hosts).<ref name="Liu-et-al-2013" /><ref name="Bolton-et-al-2008" > {{cite journal |last1=BOLTON |first1=MELVIN D. |last2=KOLMER |first2=JAMES A. |last3=GARVIN |first3=DAVID F. |title=Wheat leaf rust caused by ''Puccinia triticina'' |journal=[[Molecular Plant Pathology]] |publisher=[[Wiley-Blackwell]]/[[British Society for Plant Pathology]] |volume=9 |issue=5 |year=2008 |doi=10.1111/j.1364-3703.2008.00487.x |pages=563–575 |pmid=19018988 |pmc=6640346 }} </ref>

== Host resistance ==

Plant breeders have tried to improve yield quantities in crops like wheat from the [[history of agriculture |beginning of agriculture]]. From the 20th century, breeding for resistance against disease proved to be as important for total wheat production as breeding for increase in yield. The use of a single resistance gene against various pests and diseases plays a major role in resistance breeding for cultivated crops. The earliest single resistance gene was identified as effective against yellow rust. Numerous single genes for leaf rust resistance have since been identified.

Leaf rust resistance gene is an effective adult-plant resistance gene that increases resistance of plants against ''P. recondita'' f.sp. ''tritici'' (UVPrt2 or UVPrt13) infections, especially when combined with genes Lr13 and gene Lr34 (Kloppers & Pretorius, 1997<ref name="Kloppers-Pretorius-1997"> {{cite journal |author1=Kloppers, F. J. |author2=Pretorius, Z. A. |year=1997 |title=Effects of combinations amongst genes Lr13, Lr34 and Lr37 on components of resistance in wheat to leaf rust |journal=Plant Pathology |volume=46 |issue=5 |pages=737–750 |doi=10.1046/j.1365-3059.1997.d01-58.x }} </ref>). Lr37 originates from the French cultivar VPM1 (Dyck & Lukow, 1988<ref name="Dyck-Lukow-1988"> {{ Cite journal |author1=Dyck, P. L. |author2=Lukow, O. M. |year=1988 |title=The genetic analysis of two interspecific sources of leaf rust resistance and their effect on the quality of common wheat |journal=Canadian Journal of Plant Science |volume=68 |issue=3 |pages=633–639 |doi=10.4141/cjps88-076 |doi-access=free }} </ref>). The line RL6081, developed in Canada for Lr37 resistance, showed seedling and adult-plant resistance to leaf, yellow and stem rust. Crosses between the French cultivars will therefore introduce this gene into local germplasm, raising the genetic variation of South African cultivars.

Molecular techniques have been used to estimate genetic distances among different wheat cultivars. With the genetic distances known predictions can be made for the best combinations concerning the two foreign genotypes carrying gene Lr37, VPMI and RL6081 and local South African cultivars. This is especially important in wheat with its low genetic variation. The gene will be transferred with the least amount of backcrossing to cultivars genetically closest to each other, generation similar genetic offspring to the recurrent parent, but with gene Lr37 present. Genetic distances between near isogenic lines (NILs) for a particular gene will give an indication of how many loci, amplified with molecular techniques, need to be compared to locate putative markers linked to the gene.{{cn|date=January 2024}}

== Nomenclatural history ==

The ''Puccinia'' species causing wheat leaf rust has been called by at least six different names since 1882, when G. Winter (1882) described the ''Puccinia rubigo-vera''.<ref name="Winter 1882"> {{cite book |last=Winter |first=George |title=in Rabenhorst Kryptogamen Flora. |year=1882 |pages=924}} </ref> During this time, wheat leaf rust was interpreted as a specialized form of ''P. rubigo-vera''. Later, Eriksson and Henning (1894) classified the fungi as ''P. dispersa'' f.sp. ''tritici''.{{citation needed |date=November 2021}} In 1899, Eriksson concluded that the rust should be considered a separate authentic species. Due to this, he described the fungi as ''P. triticina''.{{citation needed |date=November 2021}} This name was used by Gauemann (1959) in his comprehensive book about rust fungi of middle Europe.<ref> {{cite book |last=Gaeumann |first=Ernst |title=Rostpilze Mitteleuropas |year=1959}} </ref>{{pn|date=January 2024}}

Mains (1933) was among the first scientists to use a species name with a broad species concept for wheat leaf rust. He considered ''P. Rubigo-vera'' a current name and posited that 32 binomials were synonyms of that species.<ref name="Mains1932"> {{cite journal |last=Mains |first=E. B. |title=Host specialization in the leaf rust of grasses, ''Puccinia rubigo-vera''. |journal=[[Papers of the Michigan Academy of Science, Arts and Letters]] |year=1932 |issue=17 |pages=289–394}} </ref> [[George Baker Cummins]] and [[Ralph Merrill Caldwell]] (1956) built off the broad species concept and also discussed the validity of ''P. rubigo-vera'', which was based on a [[Urediniospore |uredinial]]-stage [[basionym]]. Finally, they introduced ''P. recondita'' as the oldest valid name for grass-based rusts, including wheat leaf rust.<ref name="Cummins-Caldwell-1956" > {{cite journal |title=The validity of binomials in the leaf rust fungus complex of cereals and grasses |last1=Cummins |first1=George Baker |last2=Caldwell |first2=Ralph M. |journal=[[Phytopathology (journal) |Phytopathology]] |publisher=[[American Phytopathological Society]] |date=1956 |volume=46 |number=2 |pages=81–82 |issn=0031-949X |s2cid=83450378 |id=[[CAB Direct (database) |CABD]] [http://www.cabdirect.org/cabdirect/abstract/19561101781 19561101781]. [[Google Scholar |GS]] cluster [http://scholar.google.com/scholar?cluster=4553735436566102849 4553735436566102849] }} </ref> Their idea and publication was followed by Wilson & Henderson (1966) in another comprehensive rust flora (viz. British Rust Flora). Wilson and Henderson (1966) also used a broad species concept for ''P. recondita'' and divided this broad species into 11 different [[forma specialis |formae speciales]]. The accepted name for wheat leaf rust in their flora was ''P. recondita'' f.sp. ''tritici''.<ref name="Wil & Hend"> {{cite book |last=Wilson |first=M |title=British Rust Fungi |year=1966 |publisher=[[Cambridge University Press]] |isbn=9780521068390 |author2=D. M. Henderson }} </ref> Cummins (1971), in his rust monograph for [[Poaceae]], introduced an ultra-broad species concept for ''P. recondita'' and listed 52 binomials as its synonyms.<ref> {{cite book |last=Cummins |first=George Baker |title=Rust Fungi of Cereals, Grasses and Bamboos |year=1971 |publisher=Springer |isbn=9780387053363}} </ref> 

A stream of thought opposite to broad morphologically-based concepts also gained traction among uredinologists. This idea was introduced into the classification of [[graminicolous]] rust fungi by Urban (1969), who believed a taxonomic name should reflect both morphology and ecology of a species. In his paper, Urban introduced ''P. perplexans'' var. ''triticina'' as an appropriate name for wheat leaf rust.<ref name="Urban 1969"> {{cite journal |last=Urban |first=Z. |title=Die Grasrostpilze Mitteleuropas mit besonderer Brücksichtigung der Tschechoslowakei |journal=Rozpr. Cs. Akad. Ved. Ser. Mat. Prir. |year=1969}} </ref> Savile (1984) was also among the uredinologists who believed in narrowing the species concept. He considered ''P. triticina'' as an authentic taxonomic name for wheat leaf rust.<ref> {{cite book |last=Savile |first=D. B. O. |title=Taxonomy of the Cereal Rust Fungi (in The Cereal Rusts vol1) |year=1984}} </ref> Meanwhile, as his research continued Urban considered morphological, ecological, and field experiences while studying wheat leaf rust, coming to consider the fungi as a part of the species ''Puccinia persistens'' with its [[aecium |aecial]] stage on [[Ranunculaceae]] members, totally different from ''P. recondita'', which produces its aecial stage on [[Boraginaceae]] family members. His final name for this rust was ''P. persistens'' subsp. ''triticina''.<ref name="Markova1998"> {{cite journal |last=Marková |first=J |author2=Urban, Z. |title=The rust fungi of grasses in Europe. 6. ''Puccinia persistens'' |journal=Acta Univ Carol |year=1998 |volume=41 |pages=329–402}} </ref> Molecular and morphological studies proved Urban's taxonomy for wheat leaf rust to be correct.<ref name="Abbasi 2005"> {{cite journal |last=Abbasi |first=M. |author2=Ershad, D. |author3=Hedjaroude, G. A. |title=Taxonomy of ''Puccinia recondita'' s. lat. causing brown rust on grasses |journal=Iranian Journal of Plant Pathology |year=2005 |volume=41 |issue=4 |pages=631–662}} </ref>

== Life cycle ==

Wheat leaf rust spreads via airborne spores. Five types of spores are formed in the life cycle: [[Urediniospore]]s, [[teliospore]]s, and [[basidiospore]]s develop on wheat plants and [[pycniospore]]s and [[aeciospore]]s develop on the alternate hosts.<ref> {{cite book |title= A Text Book of Botany |last= Singh |first= Prof. V. |author2=Dr. P. C. Pandey |author3=Dr. D. K. Jain |year= 2008 |publisher=Rastogi |location=India |isbn= 978-81-7133-904-4 |page=15.132}} </ref> The germination process requires moisture, and works best at 100% humidity. Optimum temperature for germination is between {{convert |15–20 |C |F |0}}. Before sporulation, wheat plants appear completely asymptomatic.{{anchor |Primary host}}

=== Primary hosts ===

[[Wheat]] (''Triticum aestivum''), [[durum]] (''T. turgidum'' var. ''durum''), domesticated [[emmer]] (''T. dicoccon'') and wild emmer (''T. dicoccoides''), ''[[Aegilops speltoides]]'', jointed goatgrass (''[[Aegilops cylindrica |Ae. cylindrica]]''), and [[triticale]] (''X Triticosecale'').<ref name="Bolton-et-al-2008" />

{{anchor |Secondary host}}
=== Secondary hosts ===

Several of the [[Ranunculaceae]] serve as alternate hosts, but rarely. This does not occur with the same frequency as with stem rust and barberry.<ref group="H" name="buttercups">p.{{nbs}}5, "Wheat leaf rust has alternate hosts in the buttercup family..."</ref> ''Thalictrum speciosissimum'' (synonym ''[[Thalictrum flavum |T. flavum]] glaucum'') and ''[[Isopyrum]] [[Isopyrum fumaroides |fumaroides]]''.<ref name="Bolton-et-al-2008" />

==== ''Thalictrum flavum'' ====

''P. triticina'' has an asexual and sexual life-cycle phase. To complete its sexual phase, ''P. triticina'' requires a second host (''[[Thalictrum flavum glaucum]]'')<ref name="Bolton-et-al-2008" /> on which it will overwinter. In places where ''Thalictrum'' does not grow, such as Australia, the pathogen will only undergo its asexual life cycle and will overwinter as [[mycelium]] or [[uredinia]]. The germination process requires moisture and temperatures between {{convert |15–20 |C |F |0}}. After around 10–14 days of infection, the fungi will begin to sporulate and the symptoms will become visible on the wheat leaves.{{citation needed |date=February 2021}}

== Epidemiology ==
Location is an important characteristic in the spread of wheat rust. In some places wheat rust can easily flourish and spread. In other areas, the environment is marginally suited for the disease. Urediniospores of the wheat rusts initiate germination within one to three hours of contact with free moisture over a range of temperatures depending on the rust. Urediniospores are produced in large numbers and can be blown considerable distances by the wind, but most urediniospores are deposited close to their source under the influence of gravity. Urediniospores are relatively resilient and can survive in the field away from host plants for periods of several weeks. They can withstand freezing if their moisture content is lowered to 20 to 30 percent. Viability rapidly decreases at moisture contents of more than 50 percent. Long-distance spread of urediniospores is influenced by wind patterns and by the latitude. In general, spores move west to east due to the winds resulting from the rotation of Earth. At progressively higher latitudes, winds tend to become more southerly in the Northern Hemisphere and more northerly in the Southern Hemisphere. ''Puccinia triticina'' can survive the same environmental conditions as the wheat leaf, provided infection but no sporulation has occurred. The fungus can infect in less than three hours in the presence of moisture and temperatures below {{convert |20 |C |F |0}}; however, more infections occur with longer exposure to moisture.<ref> {{Cite book |last=Stubbs |first=R.W. |title=Cereal disease methodology manual |publisher=Mexico, DF, CIMMYT |year=1986 |pages=46}} </ref><ref> {{Cite book |last=Chester |first=K.S. |title=The nature and prevention of the cereal rusts as exemplified in the leaf rust of wheat |publisher=In Chronica botanica |location=Walthan, Massachusetts |year=1946 |pages=269}} </ref>

=== North American races ===

For the 2020 season, USDA ARS's [[Cereal Disease Laboratory]] found 36 races in North America: BBBQD, LBDSG, LCDJG, LCDSG, MBDSD, MBTNB, MCDSB, MCDSD, MCJSB, MCTNB, MLPSD, MNPSD, MPPSD, MPTSD, MSBJG, TBBGS, TBBJS, TBRKG, TBTDB, TBTNB, TCBGS, TCGJG, TCJTB, TCSQB, TCTBB, TCTNB, TCTQB, TDBGS, TFPSB, TFTSB, TGBGS, TNBGJ, TNBGS, TNBJJ, TNBJS, and TPBGJ.<ref name="USDA-ARS-2020-table" > {{cite web |url=https://www.ars.usda.gov/ARSUserFiles/50620500/Cerealrusts/2020%20WLR%20survey/WLR%202020%20Races.xlsx |archive-url=https://web.archive.org/web/20210403175445/https://www.ars.usda.gov/ARSUserFiles/50620500/Cerealrusts/2020%20WLR%20survey/WLR%202020%20Races.xlsx |title=Wheat Leaf Rust 2020 race table |archive-date=2021-04-03}} </ref><ref name="USDA-ARS-analysis" > {{cite web |archive-url=https://web.archive.org/web/20210403174600/https://www.ars.usda.gov/ARSUserFiles/50620500/Cerealrusts/2020%20WLR%20survey/Tables%201%20and%202%20WLR%202020%20Race.pdf |url=http://www.ars.usda.gov/ARSUserFiles/50620500/Cerealrusts/2020%20WLR%20survey/Tables%201%20and%202%20WLR%202020%20Race.pdf |title=Wheat Leaf Rust 2020 race analysis |archive-date=2021-04-03}} </ref>

=== Europe ===

==== Northern Europe ====

Between 1992 and 2002, of the most common [[cultivar]]s in [[Northern Europe]]an production, almost all provided [[seedling resistance]] against most pathotypes. About 1/3 of these cultivars were confirmed to carry as-yet unidentified ''Lr''s. A few cultivars were resistant to most pathotypes, and one to all of them. The most common ''Lr''s were: ''Lr13'', ''Lr14a'', and ''Lr26'', with ''Lr2a'', ''Lr3'', ''Lr10'', ''Lr17'', and ''Lr23'' occurring rarely. A few particular cultivars were extremely popular, 'Ritmo' for example being >50% of hectares/acreage in 1998 and 99. Across the entire surveyed period (92-02) the most popular were: ‘Pepital’ (''Lr10''+''Lr13''), ‘Haven’ (''Lr26''), ‘Hussar’ (''Lr26''), ‘Ritmo’ (''Lr13''), ‘Lynx’ (''Lr17''+''Lr26''), ‘Kris’ (''Lr10''+''Lr13''), ‘Terra’ (''Lr13''), ‘Sleipner’ and ‘Hereward’. (For [[spring wheat]] specifically, ‘Dragon’ (''Lr14a''), ‘Leguan’ (''Lr14a'') and ‘Vinjett’ (''Lr14a'').)<ref name="Hysing-et-al-2006" > {{ cite journal |publisher=[[BioMed Central]] (BMC) |last1=HYSING |first1=SHU-CHIN |last2=P. SINGH |first2=RAVI |last3=HUERTA-ESPINO |first3=JULIO |last4=MERKER |first4=ARNULF |last5=LILJEROTH |first5=ERLAND |last6=DIAZ |first6=OSCAR |journal=[[Hereditas]] |title=Leaf rust (''Puccinia triticina'') resistance in wheat (''Triticum aestivum'') cultivars grown in Northern Europe 1992-2002 |volume=143 |issue=2006 |date=2006-01-20 |issn=0018-0661 |doi=10.1111/j.2005.0018-0661.01917.x |pages=1–14 |pmid=17362328 |s2cid=38073701 |doi-access=free }} </ref>

== Symptoms ==

Small brown [[pustules]] develop on the leaf blades in a random scatter distribution. They may group into patches in serious cases. Onset of the disease is slow but accelerated in temperatures above {{convert |15 |C |F |0}}, making it a disease of the mature cereal plant in summer, usually too late to cause significant damage in temperate areas. Losses of between 5 and 20% are normal but may reach 50% in severe cases. Symptoms can range in severity from barely aesthetic to completely overrun on the leaf surface. On barberry leaf the disease appears as powdery yellow spots with aecia being dispersed from the underside of the leaf.

== Control ==

Varietal resistance is important. Fungicides are commonly used.<ref group="H" name="fungicides-good">p.{{nbs}}7, "Fungicides are widely used against leaf rust..."</ref> Chemical control with [[triazole fungicide]]s may be useful for control of infections up to ear emergence but is difficult to justify economically in attacks after this stage. Control often is not as common as prevention through the development of [[plant disease resistance |genetically-resilient]] varieties and the removal of [[common barberry]]. Cultivars are the best method of controlling the disease and have been utilized for over 100 years. However, resistance linked to single genes has been made ineffective by the pathogen adapting to new cultures. This is why destruction of alternate hosts is key to control. Early-maturing cultivars as well as spring wheat should be sown as early as possible to avoid peak rust periods. Self-sown wheat ([[volunteer (botany) |volunteer]]s) should be destroyed as not to further spread urediniospores at the end of harvest.<ref name="Huerta-Espino-Singh-1994" > {{cite journal |last1=Huerta-Espino |first1=Julio |last2=Singh |first2=Ravi P. |title=First Report of Virulence to Wheat with Leaf Rust Resistance Gene ''Lr19'' in Mexico |journal=[[Plant Disease (journal) |Plant Disease]] |publisher=[[American Phytopathological Society]] |volume=78 |year=1994 |issn=0191-2917 |doi=10.1094/pd-78-0640c |page=640C}} </ref><ref name="Yehuda-et-al-2004" > {{cite journal |last1=Yehuda |first1=Pnina ben |last2=Eilam |first2=Tamar |last3=Manisterski |first3=Jacob |last4=Shimoni |first4=Ayelet |last5=Anikster |first5=Yehoshua |title=Leaf Rust on ''Aegilops speltoides'' Caused by a New Forma Specialis of ''Puccinia triticina'' |journal=[[Phytopathology (journal) |Phytopathology]] |publisher=[[American Phytopathological Society]] |volume=94 |issue=1 |year=2004 |issn=0031-949X |doi=10.1094/phyto.2004.94.1.94 |pages=94–101 |pmid=18943825 |doi-access=free }} </ref> {{Tone inline |date=July 2021}}

=== Resistance genes ===

*{{anchor |Lr21}} ''Lr21'' - Scofield ''et al.'', 2005 successfully used [[virus-induced gene silencing]] to investigate how this gene works in [[hexaploid wheat]].<ref name="Downie-et-al-2021" > {{cite journal |last1=Downie |first1=Rowena C. |last2=Lin |first2=Min |last3=Corsi |first3=Beatrice |last4=Ficke |first4=Andrea |last5=Lillemo |first5=Morten |last6=Oliver |first6=Richard P. |last7=Phan |first7=Huyen T. T. |last8=Tan |first8=Kar-Chun |last9=Cockram |first9=James |title=Septoria Nodorum Blotch of Wheat: Disease Management and Resistance Breeding in the Face of Shifting Disease Dynamics and a Changing Environment |journal=[[Phytopathology (journal) |Phytopathology]] |publisher=[[American Phytopathological Society]] |date=2021-07-27 |volume=111 |issue=6 |issn=0031-949X |doi=10.1094/phyto-07-20-0280-rvw |pages= 906–920 |pmid=33245254 |hdl=20.500.11937/83208 |s2cid=227181536 |hdl-access=free }} </ref>

Because ''[[Lr34]]'', ''[[Lr46]]'', and ''[[Lr67]]'' are non-specific, they should not be used in [[race analysis]] of this pathogen.<ref name="Global-Status" />

Even the use of varieties with [[gene stack]]s has often failed against ''Pt''/''Prt'' due to individual deployment of the same genes in other varieties in the same area.<ref name="Global-Status" /> [[Slow rusting]] may be the answer.<ref name="Global-Status" >
 {{ Cite journal |date=2011 |issue=1 |publisher=[[Springer Science+Business Media]] |volume=179 |first8=H. |first7=S. |first6=W. |first5=R. |first4=B. |first3=S. |first2=R. |first1=Julio |last8=Goyeau |last7=Bhardwaj |last6=Chen |last5=Park |last4=McCallum |last3=German |last2=Singh |last1=Espino |title=Global status of wheat leaf rust caused by ''Puccinia triticina'' |journal=[[Euphytica]] |pages=143–160 |s2cid=23518560 |doi=10.1007/s10681-011-0361-x}}
</ref>

== See also==

* [[List of Puccinia species |List of ''Puccinia'' species]]
* [[Wheat diseases]]
* [[Rust (fungus)]]
* [[Rice blast]]
* [[Stem rust]]
* [[Kharchia wheat]]

== References ==

{{Reflist }}

== Further reading ==

* {{ cite report |url=http://www.bspp.org.uk/wp-content/uploads/2021/01/Ug99-Stem-Rust-4.2NH.pdf |title=Ug99 Stem Rust - overcoming wheat's defences |first=Nichola |last=Hawkins |date=2020 |publisher=[[British Society for Plant Pathology]]}}
{{reflist |group="H"}}

== External links ==

* [http://www.rust-expression.com/ www.rust-expression.com expVIP]
* {{ cite web |title=Leaf Rust |url=http://www.wheat-rust-genomics.com/leaf-rust/ |access-date=2021-05-26}}

{{Taxonbar |from=Q901658}}

[[Category:Barley diseases]]
[[Category:Rye diseases]]
[[Category:Wheat diseases]]
[[Category:Leaf diseases]]
[[Category:Fungal plant pathogens and diseases]]
[[Category:Puccinia]]