|MURITHI, HARUN - International Institute Of Tropical Agriculture (IITA)|
|BEED, FEN - International Institute For Tropical Agriculture|
|SOKO, MISHECK - Bvumbwe Agricultural Research Station|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/18/2014
Publication Date: 11/5/2014
Publication URL: http://handle.nal.usda.gov/10113/61154
Citation: Murithi, H., Beed, F., Soko, M., Haudenshield, J.S., Hartman, G.L. 2014. First report of Phakopsora pachyrhizi causing rust on soybean in Malawi. Plant Disease. 99(3):420. doi: 10.1094/PDIS-9-14-0924-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 also was reported on soybean in South Africa in 2001, in western Cameroon in 2003, in Ghana and Democratic Republic of the Congo in 2007, and in Tanzania in 2014. The typical symptoms and signs of SBR, including leaf yellowing and sporulation of the fungus, were observed on soybean leaves in May 2014 during field surveys in the major soybean growing areas of Malawi (Central: Dowa, Mchinji and Kasungu. Southern: Thyolo). SBR symptoms were observed in 9 out of 12 sites surveyed. This is the first report of rust on soybean in Malawi. 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: Soybean rust (SBR), caused by Phakopsora pachyrhizi, has rapidly become established in Africa since the first report in Uganda in 1996. The urediniospores, as windborne propagules, have infested new regions of Africa, initiating SBR in many countries, including Ghana and Democratic Republic of the Congo in 2007 and Tanzania in 2014. The typical symptoms and signs of SBR, including leaf yellowing and tan, sporulating uredinia, were observed on soybean in May 2014 during field surveys in the major soybean growing areas of Malawi (Central: Dowa, Mchinji and Kasungu. Southern: Thyolo). SBR symptoms were observed in 9 out of 12 sites surveyed. When microscopically examined, urediniospores were elliptical, echinulate, and hyaline to pale yellowish brown. 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 resulting DNA was analyzed by quantitative PCR using published Taqman assays for P. pachyrhizi and P. meibomiae, with a multiplexed exogenous internal control reaction to validate negative results. P. pachyrhizi DNA was detected in excess of 180,000 genome equivalents /cm2 in all samples, indicating a substantial infection. Urediniospores dislodged from three leaves and inoculated onto susceptible soybean cultivar Williams 82 produced tan lesions after 2 weeks of incubation in a detached-leaf assay. This is the first confirmed report of P. pachyrhizi causing rust on soybean in Malawi.