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Title: First report of Phakopsora pachyrhizi, cause of soybean rust, on Neonotoniz wightii in Paraquay

item Wilfrido, Morel
item Hernandez, Jose
item Miles, Monte
item Stone, Christine
item Frederick, Reid

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/22/2006
Publication Date: 3/1/2007
Citation: Wilfrido, M., Hernandez, J., Miles, M.R., Stone, C.L., Frederick, R.D. 2007. First report of Phakopsora pachyrhizi, cause of soybean rust, on Neonotoniz wightii in Paraquay. Plant Disease 91:325

Interpretive Summary: Asian soybean rust (ASR), caused by the fungal pathogen Phakopsora pachyrhizi, is a devastating disease in most soybean growing regions throughout the world. In 2001, ASR was discovered for the first time in South America in Paraguay. ASR has since become established on kudzu and prevalent in soybean production areas in Paraguay. In March 2006, ASR symptoms were found on the perennial legume Neonotonia wightii in the Biological Reserve (Reserva Biológica de Itabó, Dpto. Alto Paraná) in Itapúa, Paraguay. Morphological characteristics and measurements of the urediniospores were indicative of Phakopsora. Real-time polymerase chain reaction and nucleotide sequence analysis confirmed P. pachyrhizi infection. This is the first report of ASR on a host other than soybean or kudzu in South America, which may serve as a source of inoculum.

Technical Abstract: Phakopsora pachyrhizi, the cause of soybean rust, was first observed on soybean (Glycine max) in South America in the district of Itapúa in Paraguay in March, 2001. The disease is now widespread in soybean production areas in South America on soybean and kudzu (Pueraria lobata). On March 15, 2006, leaves of the perennial legume Neonotonia wightii with lesions and rust sori were observed in the Reserva Biológica de Itabó, Dpto. Alto Paraná. Lesions were scattered and most contained a single uredinium mostly hypophyllous and appeared to be new infections. Lesions with several uredinia, which are indicative of older infections on soybean, were also observed. Sori (Malupa-type) contained hyaline, peripheral, cylindric to clavate paraphyses, measuring 24 to 45 x 6 to 13 u and urediniospores that were hyaline, ovoid to globose, and measuring 20 to 40 x 14 to 25 u in size with echinulate spore wall, characters typical of Phakopsora. DNA extracted from sori from leaves of N. wightii amplified in a real-time fluorescent polymerase chain reaction using P. pachyrhizi-specific primers. Sequence alignment of the internal transcribed spacer region 2 further confirmed the identification as P. pachyrhizi. The host identification was confirmed by Dr. J. Kirkbride, USDA-ARS Systematic Botany and Mycology Laboratory (SBML), Beltsville, MD, using the Smithonian Institution Department of Botany, U.S. National Herbarium. This is the first confirmed report of natural infection of P. pachyrhizi on a host other than soybean or kudzu in South America. Voucher specimens were deposited at the Universidad Nacional de Asunción of Paraguay and the National Fungus Collection at the SBML.