|MURITHI, HARUN - International Institute For Tropical Agriculture|
|BEED, FEN - International Institute For Tropical Agriculture|
|MADATA, CATHY - Uyole Agricultural Research Institute|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/21/2014
Publication Date: 11/1/2014
Citation: Murithi, H., Beed, F., Madata, C.S., Haudenshield, J.S., Hartman, G.L. 2014. First report of Phakopsora pachyrhizi on soybean causing rust in Tanzania. Plant Disease. 98(11):1586. DX.DOI.ORG/10.1094/PDIS-06-14-0601-PDN.
Interpretive Summary: Soybean rust (SBR), caused by a fungus that spreads by producing large quantities of aerial spores, was first reported on soybean in Africa in Uganda in 1996. The fungus rapidly spread and was reported on soybean in South Africa in 2001, in western Cameroon in 2003, and in Ghana and Democratic Republic of the Congo in 2007. In 2014, leaf material collected from the Iringa and Ruvuma regions of Tanzania were observed with soybean rust. To confirm the pathogen, symptomatic soybean leaf tissue of approximately 1 cm2 was excised from each of the samples, and DNA was extracted and confirmed to be the DNA of the fungus causing soybean rust. This is the first report of rust on soybean in Tanzania. This report will be of interest to soybean pathologists throughout the world as well as other scientists interested in monitoring and detecting plant pathogens in new locations.
Technical Abstract: Phakopsora pachyrhizi Syd. was reported on legume hosts other than soybean in Tanzania as early as 1979. Soybean rust (SBR), caused by P. pachyrhizi, was first reported on soybean in Africa in Uganda in 1996, and its introduction into Africa was proposed to occur through urediniospores blowing from western India to the African east coastal areas by moist northeast monsoon winds. The fungus rapidly spread and was reported on soybean in South Africa in 2001, in western Cameroon in 2003, and in Ghana and Democratic Republic of the Congo in 2007. In 2014, sporuliferous uredinia were observed on leaf material collected from the Iringa and Ruvuma regions of Tanzania. To confirm the pathogen, symptomatic soybean leaf tissue of approximately 1 cm2 was excised from each of the samples, and DNA was extracted using the FastDNA Spin Kit (MP Biomedicals, Solon-OH), with further purification using the MicroElute DNA Clean-up Kit (Omega Bio-Tek, Norcross-GA). The DNA was subjected to quantitative PCR using published Taqman assays for P. pachyrhizi, P. meibomiae, and a multiplexed exogenous internal control reaction to validate negative results (Haudenshield). P. pachyrhizi DNA was detected in excess of 66,000 genome equivalents/cm2 in all samples, and P. meibomiae DNA was determined to be absent from all samples (limit of quantification approx. 2 pg DNA/cm2). Free surviving urediniospores were dislodged from 12 samples and inoculated onto susceptible soybean cultivar Williams 82, which produced sporulating SBR lesions after 2 weeks of incubation in a detached-leaf assay. This is the first report of P. pachyrhizi causing rust on soybean in Tanzania. In vivo cultures have been established from most of these samples, and ongoing research includes an evaluation of the P. pachyrizi virulence on a differential set, and characterization of the genetic diversity.