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ARS Home » Midwest Area » Urbana, Illinois » Soybean/maize Germplasm, Pathology, and Genetics Research » Research » Publications at this Location » Publication #336516
Title: First report of Phakopsora pachyrhizi causing rust on soybean in Ethiopia

Author
item TESFAY, ABUSH - Ethiopian Institute Of Agricultural Research
item KEFLE, BURBODE - Ethiopian Institute Of Agricultural Research
item Haudenshield, James
item Hartman, Glen

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2017
Publication Date: 3/22/2017
Citation: Tesfay, A., Kefle, B., Haudenshield, J.S., Hartman, G.L. 2017. First report of Phakopsora pachyrhizi causing rust on soybean in Ethiopia. Plant Disease. doi.org/10.1094/PDIS-11-16-1692-PDN.

Interpretive Summary: Soybean rust is caused by a fungal pathogen that spreads through air-dispersed spores. A severe epidemic caused “clouds” of spores to be observed when walking through fields in mid-October 2016 in Jimma, Ethiopia. In the first week of November, 11 samples (each representing at least five leaflets) were collected and sent by APHIS permit to the USDA-ARS Soybean Disease and Pest Laboratory in Urbana Illinois for further verification. All leaflets had uredinia and spores typical of the soybean rust pathogen. Pathogen identification was confirmed by DNA sequencing. Spores from an infected leaf induced soybean rust lesions on detached-leaves of the susceptible soybean cultivar Williams 82 two weeks after inoculation. This is the first confirmed report of the soybean rust pathogen causing rust on soybean in Ethiopia, putting at risk 30,000 ha currently under soybean production. The reports of soybean rust in Ethiopia and adjoining countries may alter soybean production practices and research interests. This information is important to epidemiologists and others interested in knowing the geographic distribution of this disease.

Technical Abstract: Soybean rust, caused by the fungal pathogen P. pachyrhizi, has been reported in 10 African countries since the first report in Uganda in 1996. In 2016, a severe epidemic caused “clouds” of urediniospores to be observed when walking through fields in mid-October 2016 in Jimma Ethiopia. In the first week of November, 11 samples (each representing at least five leaflets) were collected and sent by APHIS permit to the USDA-ARS Soybean Disease and Pest Laboratory for further verification. All leaflet had uredinia and elliptical, echinulate, and hyaline, pale yellowish-brown urediniospores. Uredinial density ranged from 5-88 (mean 42) per cm diameter based on counts from the 11 samples. In addition to uredinia, telia were observed in three of the samples. To confirm the pathogen was P. pachyrhizi, symptomatic soybean leaf tissue of less than 1 cm diameter was excised from each of the 11 samples and DNA was extracted as instructed by the manufacturer. Substantial quantities of P. pachyrhizi DNA were found in all 11 explants. Urediniospores that were dislodged from an infected leaf and inoculated in a detached-leaf assay on susceptible soybean cultivar Williams 82 resulted in tan lesions after 2 weeks of incubation. This is the first confirmed report of P. pachyrhizi causing rust on soybean in Ethiopia, putting at risk 30,000 ha currently under soybean production. The reports of soybean rust in Ethiopia and adjoining countries may alter soybean production practices and research interests. Efforts to understand the virulence and genetic diversity of the pathogen in the region will be useful to develop and deploy resistant soybean cultivars.