.

[1] South Africa: kudzu, 1st report
[2] USA (Kansas): 1st report

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[1] First report of Asian soybean rust caused by Phakopsora pachyrhizi on kudzu in South Africa
Date: Wed 26 Sep 2007
Source: The American Phytopathological Society, Plant Disease 2007; 91(10): 1364 [edited] <http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-91-10-1364C>


[Reference: Pretorius ZA et al: First report of Asian soybean rust caused by _Phakopsora pachyrhizi_ on kudzu in South Africa. Plant Dis 2007; 91(10): 1364; DOI: 10.1094/PDIS-91-10-1364C]

First report of Asian soybean rust caused by Phakopsora pachyrhizi on kudzu in South Africa

Asian soybean rust was 1st reported on soybean in South Africa (SA) in 2001 (3). The disease has occurred in all ensuing seasons, particularly in the humid, eastern production regions, causing significant losses in soybean fields not protected by fungicides.

In April 2005, rust-infected _Pueraria lobata_ (kudzu) was detected near Nelspruit, Mpumalanga, SA. At this location (25°20'41"S, 30°43'30"E), kudzu plants occurred abundantly on roadsides, edges of pine plantations, and in natural vegetation. Most vines were infected, with abaxial surfaces of older leaves often showing 100 percent severity. Following inoculation with rust spores collected from kudzu, soybean line PI200492 produced tan lesions typical of a susceptible reaction for Asian soybean rust. Lines PI230970, PI462312, and PI459025 showed
red-brown lesions typical of a resistant reaction.

Polymerase chain reaction (PCR) analysis of rust DNA extracted from primary leaves of line PI200492 infected with spores collected from kudzu positively identified the pathogen as _Phakopsora pachyrhizi_. PCR specific for _P.
meibomiae_ (1) did not yield a positive result. ELISA [enzyme linked immunosorbent assay] verified the identification of _P. pachyrhizi_ on an original kudzu sample as well as the leaf material used for DNA analysis.

A survey of kudzu at the Nelspruit site during July 2005 confirmed the presence of the pathogen during the off-season for soybean. At that time, incidence of kudzu rust remained high, but few leaves showed high severity. The susceptibility of kudzu to Asian soybean rust has been reported in controlled infection studies in SA (2). To our
knowledge, this is the 1st report of _P. pachyrhizi_ causing rust on a large, naturally occurring kudzu population in SA.

References:
1. RD Frederick et al. Phytopathology 92:217, 2002.
2. A Nunkumar. M.Sc. thesis. University of KwaZulu-Natal, South Africa, 2006.
3. ZA Pretorius et al. Plant Dis. 85:1288, 2001.

--
Communicated by:
ProMED-mail
<promed@promedmail.org> 

******

[2] First report of Asian soybean rust in Kansas, USA
Date: Fri 21 Sep 2007
Source: StopSoybeanRust, K-State/KDA news release [edited]
<http://www.stopsoybeanrust.com/viewStory.asp?StoryID=1090>

For the 1st time ever, Asian soybean rust has been confirmed in Kansas -- in a sentinel plot in Montgomery County in southeast Kansas. Officials say several hundred thousand acres of late-planted soybeans could be at risk.

Kansas State University [K-State] researchers and the Kansas Department of Agriculture [KDA] have confirmed that a leaf sample from a soybean plant collected from a sentinel plot in Montgomery County has the disease. "Asian soybean rust's arrival in Kansas was expected," said Kansas Secretary of Agriculture Adrian Polansky. "And,
we must continue to be vigilant, scouting for this disease in the coming years, to ensure we detect it early enough for growers to take action to protect their crops."

The site where the positive sample was found is one of 20 that the USDA [United States Department of Agriculture], working with KDA and K-State, planted around Kansas to monitor for the disease. "For this year [2007], this will only be a problem in late-planted soybeans," said Kansas State University plant pathologist Doug Jardine. "There are 300 000 to 400 000 acres [ca. 120 000 to 180 000 hectares] of late-planted soybeans this year [2007] that are potentially in danger. This represents about 10 percent to 15 percent of the state's crop." In university research trials during the 2005 and 2006 growing seasons, measured yield losses to soybean rust ranged from 6 percent to 32 percent, Jardine said. He anticipates that any potential yield loss in Kansas this year [2007] in the late- planted bean crop would likely be at the lower end of this range.

Soybean rust was 1st found in the United States 6 Nov 2004, in Louisiana. Since then, it has spread to several states. The disease is caused by either of 2 fungal species -- _Phakopsora pachyrhizi_, also know as the Asian species, and _Phakopsora meibomiae_, the New World species. The Asian species is the more aggressive of the 2
and causes more damage to soybean plants, said Jardine, who is the plant pathology state leader for K-State Research and Extension. The disease is spread by wind-borne spores capable of being transported over long distances.

Any soybean field that has reached the R6 stage of development (full pod fill) is no longer in danger from the disease, Jardine said. Decisions to apply a fungicide on fields that have not reached that growth stage need to be made on a field-to-field basis. The decision to spray is dependent on a combination of growth stage, application costs, expected selling price, and the yield that will be saved by spraying. Given the level of disease currently being found, yield savings would likely be no more than about 10 percent. If a fungicide application is deemed
necessary, producers are encouraged to use a triazole fungicide because the mode of action will have some curative effects on infections already in progress.

Jardine said, "Areas of the field that may be shaded, especially from the morning sun, are good places to look for rust. Pustules will be found on the bottom side of the leaflets and have the appearance of small volcanoes within the lesion." Scouting currently is more difficult in many areas of the state, due to the presence of 2 other similar-looking diseases: brown spot and bacterial blight, Jardine acknowledged.

--
Communicated by:
J. Allan Dodds
Former ProMED-mail plant disease moderator
<dodds@ucr.edu>

[The fungus _Phakopsora pachyrhizi_ was identified in Japan in 1902 as the cause of soybean rust. The fungus can cause premature defoliation, with yield losses of up to 80 percent reported in Asia. It is now widespread in
Australasia and parts of Africa (South Africa 2001) and has recently been reported from a number of countries in the Americas (USA 2004), but data are lacking concerning its establishment in Europe. It has a wide host range unusual for rust fungi, and besides soybean, a number of other species in the family of _Fabaceae_ can also be affected. Weed species can serve as pathogen reservoirs, and spores are spread by wind over long distances. Fungicides may be used in disease management and partially resistant soybean lines are available.

The less virulent related species _P. meibomiae_ is found in South America and the Caribbean and causes rust symptoms on a similar range of hosts. Previously, these 2 species were considered strains of the same species, with _P. pachyrhizi_ called the very aggressive Asian strain, and _P. meibomiae_ called the mild American strain. New strains of _P. pachyrhizi_ with increased virulence and fungicide resistances are emerging.

Brown spot is a fungal disease caused by _Septoria glycines_. Bacterial blight on soybean is caused by _Pseudomonas syringae_ pv. _glycinea_ or _P. savastanoi_ pv. _glycinea_ (there is still some debate whether these are distinct species or different strains of _P. syringae_).

The system of soybean growth stages divides plant development into vegetative (V) and reproductive (R) stages. The vegetative stages are numbered according to how many fully developed trifoliate leaves are present. The reproductive (R) stages begin at flowering and include pod development, seed development, and plant maturation. The stages can overlap.

Kudzu (_Pueraria lobata_), also called Japanese arrowroot, is a high climbing, fast growing leguminous vine which often completely covers trees, shrubs, and man-made structures. It is native to Asia where it is used as a garden
ornamental, in herbal treatments and for basketry. Vines may extend to over 30 meters (about 98 ft) in length with stems up to 10 centimeters (about 4 in) in diameter. Kudzu grows well under a wide range of conditions and soil types. It favors habitats such as forest edges, abandoned fields, roadsides, and disturbed areas where sunlight is abundant. Kudzu prefers mild winters, warm summers, and high rainfall. It was introduced as a forage plant to a number of countries becoming a widespread weed in many areas.

Maps
South Africa:
<http://www.safarinow.com/destinations/South-Africa/south-africa-map.gif>
Map of US states:
<http://www.census.gov/geo/www/us_regdiv.pdf>
Worldwide distribution of soybean rust until December 2005:
<http://www.eppo.org/QUARANTINE/Alert_List/fungi/maps/PHAKPA_map.htm>

Pictures
Soybean rust symptoms on soybean:
<http://soybeanrust.unl.edu/soybean/siteImages/plantdate.gif>  and via
<http://www.plantmanagementnetwork.org/search/image/search_action.asp?keyword=soybean+rust&type=all&imagetype=&B1=Submit>
Symptoms of the other soybean diseases via:
<http://www.ent.iastate.edu/imagegal/plantpath/soybean/>
Kudzu:
<http://oregon.gov/OISC/images/191/w_pueraria_lobata1.jpg>  and
<http://www.missouriplants.com/Bluealt/Pueraria_lobata_flowers.jpg>

Links
Information on soybean rust:
<http://www.aphis.usda.gov/plant_health/plant_pest_info/soybean_rust/downloads/UreMelPp502.pdf>,
<http://www.cps-scp.ca/pathologynews/soybeanrust.htm>  and
<http://www.eppo.org/QUARANTINE/Alert_List/fungi/PHAKPA.htm>
Diagnostic fact sheets with pictures:
<http://nt.ars-grin.gov/taxadescriptions/factsheets/index.cfm?thisapp=Phakopsorapachyrhizi> 
and
<http://extension.missouri.edu/explorepdf/agguides/crops/g04442.pdf>
Disease history and background:
<http://www.apsnet.org/online/feature/rust/>
_P. pachyrhizi_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=121037>
_P. meibomiae_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=102469>
Current information on soybean rust in the US:
<http://www.sbrusa.net/>  and
<http://www.stopsoybeanrust.com/mc_home.asp>
Soybean bacterial blight information:
<http://www.lgseeds.com/LG_Tech2/soy_bacterialblight.asp>
_Pseudomonas_ taxonomy and species list:
<http://www.bacterio.cict.fr/p/pseudomonas.html>
Soybean brown spot and bacterial blight information:
<http://www.ipm.iastate.edu/ipm/icm/1996/7-8-1996/soyfoldis.html>
_S. glycines_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=215541>
Description of soybean growth stages:
<http://extension.agron.iastate.edu/soybean/production_growthstages.html>
Decision tools for crop spraying:
<http://www.agmanager.info/crops/prodecon/production/decision/default.asp>
Information on kudzu:
<http://www.oregon.gov/ODA/PLANT/WEEDS/profile_kudzu.shtml>
KSDA:
<http://www.ksda.gov>
K-State:
<http://www.k-state.edu>
USDA:
<http://www.usda.gov/wps/portal/usdahome>.  - Mod.DHA]


[see also in the archive:
Asian soybean rust - USA: northward spread 20070804.2527
Soybean rust, Asian strain, update 2007 (02): USA 20070618.1972
Asian soybean rust, kudzu - US (LA) 20070517.1567
Asian soybean rust, plant tissue - USA (IA) 20070410.1214
Soybean rust, Asian strain, update 2007 - USA 20070318.0952
Soybean rust, Asian strain, update 2006 - USA 20070317.0942
2006
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Soybean rust, Asian strain, soybean - USA (KY): 1st report 20061017.2985
Soybean rust, Asian strain - USA (IL): 1st report 20061014.2948
2005
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Soybean rust, Asian strain - USA: 2005 disease summary 20051228.3694
Soybean rust, Asian strain, kudzu control 20051006.2914
Soybean rust, dry beans - South Africa 20050210.0452
2004
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Soybean rust - USA: 1st report 20041110.3043
2002
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Phakopsora sp., soybean rust - S. Africa, Argentina 20021231.6167
Phakopsora sp., soybean rust - South Africa 20020206.3495
2001
----
Phakopsora sp., soybean rust - South Africa (03) 20011213.3014
Phakopsora sp., soybean rust - South Africa (02) 20010405.0679
Phakopsora sp., soybean rust - S. Africa (confirmed) 20010322.0569
Phakopsora sp., soybean rust - South Africa 20010312.0505]

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