Editing Soybean rust

{{Short description|Disease affecting soybeans and other legumes}}
{{Paraphyletic group
| name = Soybean rust
| image = Soybean rust.jpg
| image_alt = Soybean leaves infected with soybean rust, uredinia are visible
| image_caption = Soybean leaves infected with soybean rust, [[Uredinium|uredinia]] are visible
| auto = yes
| parent = Phakopsora
| includes = 
*''[[Phakopsora meibomiae]]'' - New World soybean rust
*''[[Phakopsora pachyrhizi]]'' - Asian soybean rust
| excludes = 
All other ''[[Phakopsora]]'' species
}}

'''Soybean rust''' is a disease that affects [[soybean]]s and other [[legume]]s. It is caused by two types of [[fungus|fungi]], ''[[Phakopsora pachyrhizi]]'', commonly known as '''Asian soybean rust''', and ''[[Phakopsora meibomiae]]'', commonly known as '''New World soybean rust'''. ''P. meibomiae'' is the weaker [[pathogen]] of the two and generally does not cause widespread problems. The disease has been reported across [[Asia]], [[Australia]], [[Africa]], South America and the United States.

==Importance==
Soybean is one of the most important commercial crops around the world. Asian soybean rust is the major disease that affects soybeans. It causes [[lesion]]s on the leaves of soybean plants and eventually kills the plants. The disease has caused serious yield loss of soybeans.<ref name="InvasiveSpecies.gov" /> In the areas where this disease is common, the yield losses can be up to 80%.<ref name="OSU" /> The first reported cases in the United States occurred in 2004.<ref name = "Current-Status" /> This population originated in [[northern South America]] or the [[Caribbean]].<ref name = "Current-Status" /> The spores were most likely spread by [[Hurricane Ivan]].<ref name = "Current-Status" >{{cite journal | last1=Singh | first1=R. P. | last2=Hodson | first2=D. P. | last3=Jin | first3=Yue | last4=Huerta-Espino | first4=J. | last5=Kinyua | first5=M. G. | last6=Wanyera | first6=R. | last7=Njau | first7=P. | last8=Ward | first8=R. W. | title=Current status, likely migration and strategies to mitigate the threat to wheat production from rzace Ug99 (TTKS) of stem rust pathogen. | journal=CABI Reviews | publisher=CABI Publishing | year=2006 | volume=2006 | issn=1749-8848 | doi=10.1079/pavsnnr20061054| doi-access=free }}</ref><ref name="OSU">{{Cite web |title=Soybean Rust |url=https://ohioline.osu.edu/factsheet/plpath-soy-2 |access-date=2022-05-07 |website=ohioline.osu.edu |language=en}}</ref> In 2002, [[United States Department of Agriculture|USDA]] reported 10-60% yield losses in South America and Africa.<ref name="IFTD" /> in countries where this pathogen is established, estimated  losses are between 10 and 80% depending on the inoculation and environmental conditions.<ref>{{Cite web |title=Soybean Rust |url=https://extension.missouri.edu/publications/g4442?p=1 |access-date=2022-05-07 |website=extension.missouri.edu |language=en}}</ref>

==Host and symptoms==
Soybean rust is caused by two types of fungi, ''[[Phakopsora pachyrhizi]]'' and ''[[Phakopsora meibomiae]]''.<ref name="APHIS" /> It affects several important commercial plants, however, most notable for soybeans. Asian Soybean Rust can infect and reproduce on 90 known plant species, 20 of which are found in the United States, such as, soybeans, [[Common bean|dry beans]], [[Common bean|kidney beans]], [[pea]]s. Asian soybean rust also infects yellow sweet lover, vetch, medic, lupine, green and kidney bean, and lima and butter bean.<ref>{{Cite web |title=Asian Soybean Rust {{!}} Integrated Crop Management |url=https://crops.extension.iastate.edu/soybean/diseases_rust.html |access-date=2022-05-07 |website=crops.extension.iastate.edu}}</ref> leguminous forage crops such as trefoil and sweet clover and weeds such as [[kudzu]].<ref name="InvasiveSpecies.gov" /> 
[[File:Phakopsora pachyrhizi 1.jpg|right|thumb|Soybean leaves infected with ASR (photo from USDA)<ref name="USDA-ARS" />]]

At the early stage of Asian Soybean Rust, it causes yellow mosaic discoloration on the upper surfaces of older foliage. At this stage, it is usually hard to identify since the symptoms are relatively small and poorly defined.<ref name="APHIS-factsheet" />

Later as the disease continues to progress, the leaves will turn yellow and there will be lesions mostly on the undersides of the leaves and sometimes on [[petiole (botany)|petioles]], stems or pods and premature defoliation can also be observed.<ref name="ppwsipm.contentsrvr.net" /> In Phakopsora pachyrhizi  will begin to form small brown and brick red sports on the lower canopy of the leaves that will begin to turn into lesions.
  
Asian Soybean Rust produces two types of lesions. Lesions at the later stage will turn from gray to tan or reddish brown.  Mature tan lesions consist of small pustules surrounded by discolored [[necrosis|necrotic]] areas. Tan spores can be found at the necrotic areas on the underside of the leaf. In the case of reddish brown lesions, there are larger reddish brown necrotic areas with few pustules and visible spores on the underside of the leaf. A good way to distinguish Asian Soybean Rust from other diseases is to look at the pustules it produces. ASR pustules usually do not have the yellow halo which is typical of [[bacteria]]l pustules. Besides, ASR pustules are raised and can be commonly found on the underside of the leaf which makes it different from the lesions caused by spot diseases.<ref name="APHIS-factsheet" /><ref name="Invasive.org" />

Soybean plants are one of ASR's most known hosts and are susceptible at any stage in the life cycle. However, symptoms are most commonly found during or after flowering.<ref name="planthealth.info-symptoms" /> ASR infection will reduce pod production and fill.<ref name="ppwsipm.contentsrvr.net" />

==Environment==
Asian Soybean Rust (ASR) was first detected in Asia.<ref name="InvasiveSpecies.gov" /> It has been found in many countries around the world since then. For example, [[Australia]], [[China]], [[Korea]], [[India]], [[Japan]], [[Nepal]], [[Taiwan]], [[Thailand]], the [[Philippines]], [[Mozambique]], [[Nigeria]], [[Rwanda]], [[Uganda]], [[Zimbabwe]], [[South Africa]], [[Brazil]], [[Argentina]], and [[Paraguay]]. This disease was first detected in the [[Caribbean Sea|Caribbean]] in [[Puerto Rico]] in 1976<ref name="APHIS" /> and first reported in the [[continental United States]] in 2004.<ref name="InvasiveSpecies.gov" />

Asian Soybean Rust favors environments that are humid and warm. A continuous period of wetness on leaves will aid the growth of this disease since this situation is required for spores to germinate. Therefore, is most likely to appear under conditions of {{convert|60 to 85|F|C}} and a relative humidity of 75% to 80%. Therefore, ASR is a more serious problem in [[tropical]] and [[subtropical]] areas in Asia, Africa, Australia and South America.<ref name="InvasiveSpecies.gov" /> It is unable to survive the cold winters of northern habitats. However, this pathogen can be spread easily from wind and storm fronts and can inoculate quickly within a soybean field under favorable environmental conditions.<ref name="OSU"/> And the Asian Soybean Rust may be favored by the climatic anomalies phenomena that cause extreme rainfall natural disasters that is called [[El Niño]].<ref>{{Cite web |url=https://www.agrolink.com.br/noticias/alerta--el-nino-pode-favorecer-ferrugem-asiatica-no-brasil_477900.html |title=ALERTA: El Niño pode favorecer ferrugem asiática no Brasil |publisher=Agrolink |date= 31 March 2023 |access-date= 31 March 2023 |language=pt}}</ref>

==Disease cycle==
[[Soybean]] rust is spread by windblown spores and has caused significant crop losses in many soybean-growing regions of the world.<ref name="ppdl.purdue.edu" /> Windblown spores can travel for great distances and are released in cycles of seven days to two weeks. It is likely that ASR will survive on vast acreages of naturalized kudzu in the southern U.S. and thereby establish a permanent presence in the continental U.S. It is commonly believed that the disease was carried from [[Venezuela]] to the [[United States]] by [[Hurricane Ivan]].<ref name="Schneider2005" />

''P. pachyrhizi'' is an obligate parasite, meaning that it must have live, green tissue to survive.  For this reason ASR is something that will blow in every year, as cold winters will push it back. It can [[overwinter]] in southern states, so long as it has a living host.

ASR overwinters on live host [[legume]]s and [[Spore|sporulates]] the following spring. It cannot survive on dead tissue or crop residues.<ref name="Born-Diver-2005" />

Additional hosts can serve as overwintering reservoirs for the pathogen and allow for build-up of [[Inoculation|inoculum]], in those environs free from freezing temperatures.  The pathogen is well adapted for long-distance dispersal, because spores can be readily carried long distances by the wind to new, rust-free regions.<ref name="ppdl.purdue.edu" />

Overwintering sites of soybean rust are restricted to areas with very mild winters, such as the [[Gulf Coast of the United States|gulf coasts]] of Florida, the very southernmost areas of [[Texas]], or in [[Mexico]]. Soybean rust will not survive over the winter in the North Central region because it can't live and reproduce without green living tissue.<ref name="planthealth.info-basics" />

Spores of the soybean rust pathogen are transported readily by air currents and can be carried hundreds of miles in a few days. Weather conditions will determine when and where the spores travel from south to north.

Rust spores, called [[urediniospore]]s, are able to penetrate the plant cells directly, rather than through natural openings or through wounds in the leaf tissue. Thus [[infection]] is relatively quick: about 9 to 10 days from initial infection to the next cycle of spore production.

Rust is a multi-cyclic disease. After the initial infection is established, the infection site can produce spores for 10 to 14 days. Abundant spore production occurs during wet leaf periods (in the form of rain or dew) of at least 8 hours and moderate temperatures of {{convert|60 to 80|F|C}}.<ref name="planthealth.info-basics" />

===The process===
The infection process starts when urediniospores germinate to produce a single [[germ tube]] that grows across the leaf surface, until an [[appressorium]] forms. Appressoria form over [[Anticline|anticlinal]] walls or over the center of [[Epidermis (botany)|epidermal]] cells, but rarely over [[stoma]]ta. Penetration of epidermal cells is by direct penetration through the cuticle by an appressorial peg. When appressoria form over stomata, the [[hypha]]e penetrate one of the guard cells rather than entering the leaf through the stomatal opening. This rust and related species are unique in their ability to directly penetrate the epidermis; most rust pathogens enter the leaf through stomatal openings and penetrate cells once inside the leaf. The direct penetration of the epidermal cells and the non-specific induction of appressoria in the infection process of ''P. pachyrhizi'' may aid in understanding the broad host range of the pathogen and may have consequences in the development of resistant cultivars.<ref name="soybeanrust.org" />

Uredinia can develop 5 to 8 days after infection by urediniospores. The first urediniospores can be produced as early as 9 days after infection, and spore production can continue for up to 3 weeks. Uredinia may develop for up to 4 weeks after a single inoculation, and secondary uredinia will arise on the margins of the initial infections for an additional 8 weeks. Thus, from an initial infection, there could be first generation pustules that maintain sporulation for up to 15 weeks. Even under dry conditions this extended sporulation capacity allows the pathogen to persist and remain a threat. If conditions for re-infection are sporadic throughout the season, significant inoculum potential still remains from the initial infection to reestablish an epidemic. Successful infection is dependent on the availability of moisture on plant surfaces. At least 6 hours of free moisture is needed for infection with maximum infections occurring with 10 to 12 hours of free moisture. Temperatures between {{convert|15 and 28|C|F}} are ideal for infection.<ref name="soybeanrust.org" />

==Management and control==
Disease control options for ASR are limited. Rust descends in clouds of spores across the countryside. Cultural practices such as row spacing and [[crop rotation]]s have little effect. [[plant disease resistance|Resistant]] [[cultivar]]s do exist,<ref name="Kashiwa-et-al-2020" /><ref name="Langenbach-et-al-2016" /> carrying what are called ''Rpp'' genes.<ref name="Kashiwa-et-al-2020" /><ref name="Langenbach-et-al-2016" /> When weather and disease infection conditions are favorable, the occurrence of ASR can be widespread. Thus, remedial control measures—using [[fungicide]]s as protective sprays—are the main effective disease control method.<ref name="Born-Diver-2005" /><ref name="Kashiwa-et-al-2020" /><ref name="Langenbach-et-al-2016" />  Soybean rust must be managed as early in the growing season as possible to be managed successfully.<ref>{{Cite web |title=Soybean rust |url=https://extension.umn.edu/pest-management/soybean-rust |access-date=2022-05-04 |website=extension.umn.edu |language=en}}</ref>

Synthetic fungicides are the primary disease control option for protection against Asian soybean rust. The cost of spraying is estimated to be about $15 to $20 per [[acre]]; however, two or three sprays may be needed over the course of the growing season. These are significant additional production costs for soybean growers.<ref name="Born-Diver-2005" />

Fungicide screening trials to determine disease control efficacy have been field conducted in South America and South Africa. These reports are available on the Web through USDA's Integrated Pest Management Information Centers.<ref name="IMP-Centers" /> These research trials form the basis for fungicidal recommendations in the U.S.

Recent research from [[Washington State University]] indicates that the herbicide [[Glyphosate]] may be effective in dealing with the fungus.{{citation needed|date=October 2015}}

Rust-resistant varieties of soybeans are currently in development by both public universities and private industry.<ref name="Kashiwa-et-al-2020" /><ref name="Langenbach-et-al-2016" />

In some regions, the selection of winter cover crops and forage legumes may be effected, since they can serve as host plants.<ref name="Born-Diver-2005" /> Resistance genes (''Rpp''s) have been identified<ref name="Kashiwa-et-al-2020" /><ref name="Langenbach-et-al-2016" /> and host resistance is expected to be an effective, long-term solution for soybean rust in the future.<ref name="Kashiwa-et-al-2020" /><ref name="Langenbach-et-al-2016" />  Until resistant commercial varieties are in place, the management of rust depends on judicious use of fungicides.<ref name="planthealth.info-basics" /><ref name="Kashiwa-et-al-2020" /><ref name="Langenbach-et-al-2016" />

When untreated, soybean rust causes yield losses due to premature defoliation, fewer seeds per pod and decreased number of filled pods per plant.<ref name="ppdl.purdue.edu" />

==See also==
* [[Rust (fungus)]]
* ''[[Phakopsora gossypii]]'' also known as cotton rust
* [[Soybean dwarf virus]]

==References==
{{Reflist|refs=
<ref name="InvasiveSpecies.gov">{{cite web | title=Soybean Rust | website=[[National Invasive Species Information Center]] | date=2012-02-24 | url=http://www.invasivespeciesinfo.gov/profile/soybean-rust | access-date=2020-12-06}}</ref>
<ref name="IFTD">{{cite web | title=Institute for Technology Development | website=iftd.org | date=2007-07-26 | url=http://www.iftd.org/soybean_rust.php | archive-url=https://web.archive.org/web/20070726203759/http://www.iftd.org/soybean_rust.php | archive-date=2007-07-26 | url-status=unfit | access-date=2020-12-06}}</ref>
<ref name="APHIS">{{cite web | title=Plant Pests and Diseases | website=[[United States Department of Agriculture]] [[Animal and Plant Health Inspection Service]] | url=http://www.aphis.usda.gov/plant_health/plant_pest_info/soybean_rust/index.shtml | access-date=2020-12-06 | archive-date=2013-10-01 | archive-url=https://web.archive.org/web/20131001103045/http://www.aphis.usda.gov/plant_health/plant_pest_info/soybean_rust/index.shtml | url-status=dead }}</ref>
<ref name="USDA-ARS">{{cite web | title=Científicos identifican los genes de soya que proveen resistencia contra la roya / 26 de marzo 2009 / Noticias del Servicio de Investigación Agrícola, USDA | website=[[Agricultural Research Service]] [[United States Department of Agriculture]] | date=2009-05-12 | url=http://www.ars.usda.gov/is/espanol/pr/2009/090326.es.htm | archive-url=https://web.archive.org/web/20090512231502/http://www.ars.usda.gov/is/espanol/pr/2009/090326.es.htm | archive-date=2009-05-12  | language=es | access-date=2020-12-06}}</ref>
<ref name="APHIS-factsheet">{{cite web|url=http://www.aphis.usda.gov/publications/plant_health/content/printable_version/faq_phsoybeanrust.pdf|title=Factsheet - Plant Protection and Quarantine - May 2004 - Soybean Rust|archive-url=https://web.archive.org/web/20060927051015/http://www.aphis.usda.gov/publications/plant_health/content/printable_version/faq_phsoybeanrust.pdf|archive-date=2006-09-27}}</ref>
<ref name="Invasive.org">{{cite web | title=USDA Confirms Soybean Rust in United States - Invasive and Exotic Species of North America | website=Invasive.org | date=2006-02-12 | url=http://www.invasive.org/pests/soybeanrust/nr111004.cfm | archive-url=https://web.archive.org/web/20060212025950/http://www.invasive.org/pests/soybeanrust/nr111004.cfm | archive-date=2006-02-12  | access-date=2020-12-06}}</ref>
<ref name="ppwsipm.contentsrvr.net">{{cite web | title=Virginia Asian Soybean Rust | website=ppwsipm.contentsrvr.net | date=2008-07-06 | url=http://ppwsipm.contentsrvr.net/asr_identification.php#ASR%20Symptoms%20on%20Soybeans | archive-url=https://web.archive.org/web/20080706133158/http://ppwsipm.contentsrvr.net/asr_identification.php#ASR%20Symptoms%20on%20Soybeans | archive-date=2008-07-06  | access-date=2020-12-06}}</ref>
<ref name="planthealth.info-symptoms">{{cite web | title=Plant Health Initiative | website=planthealth.info | date=2005-03-15 | url=http://www.planthealth.info/rust_symptoms.htm | archive-url=https://web.archive.org/web/20050315184741/http://www.planthealth.info/rust_symptoms.htm | archive-date=2005-03-15 | url-status=unfit | access-date=2020-12-06}}</ref>
<ref name="Born-Diver-2005">{{cite web | last1=Born | first1=Holly | last2=Diver | first2=Steve | title=Asian Soybean Rust: Notes and Organic Control Options for Farmers | website=attra.ncat.org | date=2005-11-28 | url=http://attra.ncat.org/attra-pub/asian_soy_rust.html | archive-url=https://web.archive.org/web/20051128034038/http://attra.ncat.org/attra-pub/asian_soy_rust.html | archive-date=2005-11-28  | access-date=2020-12-06}}</ref>
<ref name="ppdl.purdue.edu">{{cite web | title=Soybean Rust - Plant and Pest Diagnostic Laboratory, Purdue University | website=ppdl.purdue.edu | date=2004-10-16 | url=http://www.ppdl.purdue.edu/PPDL/soybean_rust.html | archive-url=https://web.archive.org/web/20041016111451/http://www.ppdl.purdue.edu/PPDL/soybean_rust.html | archive-date=2004-10-16  | access-date=2020-12-06}}</ref>
<ref name="planthealth.info-basics">{{cite web | title=Plant Health Initiative | website=planthealth.info | date=2005-03-09 | url=http://www.planthealth.info/rust_basics.htm | archive-url=https://web.archive.org/web/20050309094237/http://www.planthealth.info/rust_basics.htm | archive-date=2005-03-09  | access-date=2020-12-06}}</ref>
<ref name="soybeanrust.org">{{cite web | title=Illinois Soybean Rust Information Center | website=soybeanrust.org | date=2006-08-19 | url=http://www.soybeanrust.org/symptoms_etc.htm | archive-url=https://web.archive.org/web/20060819045525/http://www.soybeanrust.org/symptoms_etc.htm | archive-date=2006-08-19  | access-date=2020-12-06}}</ref>
<ref name="IMP-Centers">{{cite web | url=http://www.ipmcenters.org/newsalerts/soybeanrust/efficacy.cfm | title=National Site for the Regional IPM Centers | access-date=2015-10-16 | archive-date=2015-09-24 | archive-url=https://web.archive.org/web/20150924040018/http://www.ipmcenters.org/newsalerts/soybeanrust/efficacy.cfm | url-status=dead }}</ref>
<ref name="Kashiwa-et-al-2020">{{cite journal |author=Kashiwa, T. |author2=Muraki, Y. |author3=Yamanaka, N. |volume=10|page=13270|doi=10.1038/s41598-020-70188-7|title=Near-isogenic soybean lines carrying Asian soybean rust resistance genes for practical pathogenicity validation | journal=Scientific Reports | date=2020-08-06 |issue=1|pmid=32764613|pmc=7411041|bibcode=2020NatSR..1013270K}}</ref>
<ref name="Langenbach-et-al-2016">{{cite journal | last1=Langenbach | first1=Caspar | last2=Campe | first2=Ruth | last3=Beyer | first3=Sebastian F. | last4=Mueller | first4=André N. | last5=Conrath | first5=Uwe | title=Fighting Asian Soybean Rust | journal=[[Frontiers in Plant Science]] | publisher=[[Frontiers Media]] SA | volume=7 | date=2016-06-07 | page=797 | issn=1664-462X | doi=10.3389/fpls.2016.00797| pmid=27375652 | pmc=4894884 | doi-access=free }}</ref>
<ref name="Schneider2005">{{cite journal |author=Schneider, RW |author2=Hollier, CA |author3=Whitam, HK |author4=Palm, ME | author5=McKemy, JM | author6=Hernández, JR | author7=Levy, L | author8=DeVries-Paterson, R |volume=89|issue=7|page=774|doi=10.1094/PD-89-0774A|title=First Report of Soybean Rust Caused by Phakopsora pachyrhizi in the Continental United States | journal=Plant Disease | date=2005-07-01 |pmid=30791253|url=https://apsjournals.apsnet.org/doi/10.1094/PD-89-0774A|doi-access=free }}</ref>
}}

==Further reading==
* {{cite journal | last1=Frederick | first1=Reid D. | last2=Snyder | first2=Christine L. | last3=Peterson | first3=Gary L. | last4=Bonde | first4=Morris R. | title=Polymerase Chain Reaction Assays for the Detection and Discrimination of the Soybean Rust Pathogens ''Phakopsora pachyrhizi'' and ''P. meibomiae'' | journal=[[Phytopathology (journal)|Phytopathology]] | publisher=[[American Phytopathological Society]] | volume=92 | issue=2 | year=2002 | issn=0031-949X | doi=10.1094/phyto.2002.92.2.217 | pages=217–227| pmid=18943097 }}
* {{cite journal | last1=Bonde | first1=M. R. | last2=Nester | first2=S. E. | last3=Austin | first3=C. N. | last4=Stone | first4=C. L. | last5=Frederick | first5=R. D. | last6=Hartman | first6=G. L. | last7=Miles | first7=M. R. | title=Evaluation of Virulence of ''Phakopsora pachyrhizi'' and ''P. meibomiae'' Isolates | journal=[[Plant Disease (journal)|Plant Disease]] | publisher=[[American Phytopathological Society]] | volume=90 | issue=6 | year=2006 | issn=0191-2917 | doi=10.1094/pd-90-0708 | pages=708–716| pmid=30781228 }}

==External links==
* [https://ssnavi.public.iastate.edu/MF2680-1.pdf Using Foliar Fungicides to Manage Soybean Rust] {{Webarchive|url=https://web.archive.org/web/20100707052703/http://ssnavi.public.iastate.edu/MF2680-1.pdf |date=2010-07-07 }}
* {{cite web | url=http://uspest.org/risk/sbr_map | title=Botrytis and (Experimental) Soybean Rust Model Map}}
* {{cite web | url=https://www.invasivespeciesinfo.gov/profile/soybean-rust |title = Soybean Rust &#124; National Invasive Species Information Center &#124; USDA}}, National Invasive Species Information Center, [[United States National Agricultural Library]]. Lists general information and resources for Soybean Rust.
* {{cite web | title=Norwich Rust Group | website=Norwich Rust Group | url=http://www.norwichrustgroup.com/ | archive-url=https://web.archive.org/web/20150313041327/http://www.norwichrustgroup.com/ | url-status=dead | archive-date=March 13, 2015 | access-date=2020-12-18 }}
* {{cite web | title=''Phakopsora meibomiae'' (soybean rust) | website=[[Centre for Agriculture and Bioscience International]] - [[Invasive Species Compendium]] | date=2019-11-22 | url=http://www.cabi.org/isc/datasheet/40018 | access-date=2021-01-28}}

[[Category:Pucciniales]]
[[Category:Fungal plant pathogens and diseases]]
[[Category:Soybean diseases]]
[[Category:Fungus common names]]