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Date: September 17, 2007
Source: The American Phytopathological Society, Plant Disease 2007; 91(9): 1204 [edited]
<http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-91-9-1204C>

[Reference: PS Ojiambo et al: First report of rust caused by _Phakopsora pachyrhizi_ on soybean in Democratic Republic of Congo. Plant Dis 2007;
91(9): 1204; DOI: 10.1094/PDIS-91-9-1204C]

1st report of rust caused by _Phakopsora pachyrhizi_ on soybean in Democratic Republic of Congo

Nigeria (1) and Uganda (3) are the closest countries to the Democratic Republic of Congo (DRC) where soybean rust caused by _Phakopsora pachyrhizi_ has been reported. In February 2007, during a disease survey in DRC, soybean (_Glycine max_) leaves with rust symptoms (tan, angular lesions with erumpent sori exuding urediniospores) were observed in 10 fields in the following areas in Bas Congo Province: Bangu, Kimpese, Kolo-Fuma, Lukala, Mbanza-Ngungu, Mpalukide, Mvuazi, and Ntemo. Rust incidence in these fields ranged from 85 to 100 per cent, while severity ranged between 3 and 35 per cent of the leaf area on infected plants.

Urediniospores were hyaline [transparent], minutely echinulate [set with small spines], and 23 to 31 by 16 to 20 micrometers. Within a week of collection, infected leaf samples were sent to the USDA-ARS [USA Department of Agriculture-Agricultural Research Service] Foreign Disease-Weed Science Research Unit (FDWSRU) for pathogen identification. DNA was extracted from sections of leaves containing sori, and all 10 field samples amplified in a real-time fluorescent PCR [polymerase chain reaction] with _P.
pachyrhizi_-specific primers (2).

Infected leaves of cultivar Vuangi collected from one field each in the INERA [Institut de l'Environnement et Recherches Agricoles] Research Station, Kimpese-Crawford, and Kimpese-Ceco were separately washed in sterile water to collect urediniospores that were used to separately inoculate 3 detached leaves of susceptible cultivar TGx 1485-1D (4).
Lesions on inoculated leaves developed 5 days after inoculation (DAI), and pustules (110 to 130 micrometers) formed 7 DAI and erupted 2 days later exuding columns of urediniospores similar in size to the initially collected isolates. Inoculation of another set of detached leaves with a spore suspension from the 1st set of detached leaves resulted in typical rust symptoms.

Seedlings of cultivar Williams also showed typical rust symptoms when inoculated separately with urediniospores collected from 9 fields (that is, all except Kimpese-Ceco, which was infective in the detached leaf assay).
Inoculation and incubation were carried out at the FDWSRU Plant Pathogen Containment Facility at Fort Detrick [Maryland, USA] as described earlier (2).

The PCR assay, morphological characters of the isolates, and pathogenicity tests demonstrate that _P. pachyrhizi_ occurs in DRC. To our knowledge, this is the 1st report of _P. pachyrhizi_ infecting soybean in DRC.

References:
1. OA Akinsanmi, et al. Plant Dis 2001; 85: 97.
2. RD Frederick, et al. Phytopathology 2002; 92: 217.
3. E Kawuki, et al. J Phytopathol 2003; 151: 7.
4. M Twizeyimana, et al. Plant Management Network, 2006. Online publication <http://www.plantmanagementnetwork.org/infocenter/topic/soybeanrust/2006/posters/41.asp>

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[The fungus _Phakopsora pachyrhizi_ was identified in Japan in 1902 as the cause of soybean rust. It was 1st confirmed on the African continent on soybean in central Uganda in 1996, although several unsubstantiated reports suggest an earlier presence on other legumes. The fungus can cause premature defoliation, with yield losses of up to 80 per cent reported in Asia. It is now widespread in Australasia and parts of Africa and has recently been reported from a number of countries in the Americas, 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.

A 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.

TGx lines are newly developed African soybean cultivars known as Tropical Glycine cross (TGx). They are able to nodulate with _Brachyrhizobium_ spp. that are indigenous to African soils.

Maps
Democratic Republic of the Congo:
<http://www.un.org/Depts/Cartographic/map/profile/drcongo.pdf>
Bas Congo:
<http://www.berggorilla.org/english/gjournal/texte/33bas-congo.html>
Administrative zones of DRC:
<http://www.congonline.com/geo/zonesadm.htm>
Africa, overview:
<http://www.lib.utexas.edu/maps/africa/africa_pol97.jpg>
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>
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>
<http://www.eppo.org/QUARANTINE/Alert_List/fungi/PHAKPA.htm>
Diagnostic fact sheet with pictures:
<http://nt.ars-grin.gov/taxadescriptions/factsheets/index.cfm?thisapp=Phakopsorapachyrhizi> 

Disease history and background:
<http://www.apsnet.org/online/feature/rust/>
Soybean rust arrival in Africa:
<http://www.apsnet.org/pd/summaries/djn05sum.asp>
_P. pachyrhizi_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=121037>
_P. meibomiae_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=102469>
Information on breeding African soybean cultivars:
<http://www.iita.org/cms/details/soybean_project_details.aspx?zoneid=63&articleid=270> 

USDA-ARS:
<http://www.ars.usda.gov/main/main.htm>
INERA:
<http://www.inera.bf>.  - Mod.DHA]

[see also in the archive:
Asian soybean rust - Ghana: 1st report 20070820.2710
2005
---
Soybean rust, dry beans - South Africa 20050210.0452
2004
---
Soybean rust - Zimbabwe 20040212.0463
2003
---
Soybean rust - Zimbabwe (Arcturus) 20030222.0456 Phakopsora sp., soybean, yield loss - Uganda 20030119.0176
2002
---
Phakopsora sp., soybean rust - S. Africa, Argentina 20021231.6167 Phakopsora sp., soybean rust - South Africa 20020206.3495 Phakopsora sp., rust, soybean - Zimbabwe 20020110.3220
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 Phakopsora sp., soybean rust - Africa (02) 20010310.0491 Phakopsora sp., soybean rust - Africa 20010309.0487 Phakopsora sp., soybean rust - Nigeria 20010309.0486]

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