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Date: August, 2007
Source: The American Phytopathological Society, Plant Disease 2007; 91(8): 1057 [edited]
<http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-91-8-1057B>

[Reference:
R. Bandyopadhyay et al: First Report of Soybean Rust Caused by _Phakopsora pachyrhizi_ in Ghana. Plant Dis 2007; 91(8): 1057; DOI: 10.1094/PDIS-91-8-1057B]

First report of soybean rust caused by Phakopsora pachyrhizi in Ghana

Nigeria is the only country in West Africa where soybean rust, caused by _Phakopsora pachyrhizi_, has been officially reported (1). During a disease survey in Ghana during October 2006, soybean (_Glycine max_) leaves with rust symptoms (tan, angular lesions with erumpent sori [clusters of spore-producing structures] exuding urediniospores) were observed in 11 fields in the following districts: Kassena Nankana in the Upper East Region; East Gonja, Central Gonja, and Tolon-Kumbungu in the Northern Region; and Ejisu-Juabeng in the Ashanti Region. Disease incidence in these fields ranged from 50 to 100 percent and disease severity ranged between 3 and 40 percent of the leaf area on infected plants.

Urediniospores were hyaline [transparent], minutely echinulate [set with small spines], and 23 to 31 by 14 to 18 micrometers. Within a week of collection, leaf samples were sent to the USDA-ARS (US Department of Agriculture-Agricultural Research Service) Foreign Disease-Weed Science Research Unit for verification of pathogen identity. DNA was extracted from leaf pieces containing sori, and all 11 field samples amplified in a real-time fluorescent polymerase chain reaction (PCR) with _P. pachyrhizi_-specific primers (2). Sequence alignment further confirmed the identification as _P. pachyrhizi_ (2).

Infected leaves from 3 fields were separately washed in sterile water to collect urediniospores that were used to separately inoculate 3 detached leaves (for each isolate) of a susceptible soybean cultivar (TGx line; 3). Lesions on inoculated leaves developed 5 to 6 days after inoculation (DAI), and pustules (105 to 120 micrometers) formed 7 to 8 DAI and erupted 3 days later exuding columns of urediniospores similar in size to the initially collected isolates. Inoculating another set of detached leaves with a spore suspension from the 1st set of detached leaves resulted in typical rust symptoms.

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

References:
1. O. A. Akinsanmi et al. Plant Dis. 85:97, 2001
2. R. D. Frederick et al. Phytopathology 92:217, 2002
3. 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 percent 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 also 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., which are indigenous to African soils.

Maps
Ghana:
<http://www.lib.utexas.edu/maps/africa/ghana_pol96.jpg>
Ghana regions (with list of districts):
<http://www.ghanadistricts.com/home/?_=27>
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>, and
<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>
- Mod.DHA]

[see also in the archive:
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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