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First Report of Asian Soybean Rust Caused by Phakopsora pachyrhizi from Mexico

Leaves of soybean (Glycine max (L.) Merr.; Fabaceae) cv. Huasteca 400, with conspicuous chlorotic spots and associated hypophyllous cinnamon-brown sori, were collected in commercial soybean plantings in Ébano and Tamuín in the state of San Luis de Potosí, Mexico on 26 October 2005. Uredinia, Malupa-type, are mostly hypophyllous, minute, pulverulent, cinnamon-brown, scattered or in groups, subepidermal becoming erumpent, cone like, surrounded by paraphyses; paraphyses are cylindric to clavate, 25 to 50 × 6 to 14 μm, colorless to yellow brownish with wall thickened at the apex. Urediniospores are obovoid to broadly ellipsoidal, measuring 18 to 37 × 15 to 24 μm, and have a minutely echinulate thin wall, hyaline to pale yellowish brown. This morphology is typical of Phakopsora pachyrhizi Syd. & P. Syd. and P. meibomiae (Arthur) Arthur. DNA was extracted from leaves containing sori with the PureLink Plant DNA Reagent (Invitrogen, Carlsbad, CA), and the identity of P. pachyrhizi was confirmed by the polymerase chain reaction protocol (1) with Ppa1/Ppa2 primers at the National Phytosanitary Reference Center of Mexico. The morphological and molecular diagnosis and presence of P. pachyrhizi in Mexico was officially communicated by the North American Plant Protection Organization (NAPPO) on 16 February 2006. Asian soybean rust was reported for the first time in North America in 2004 (2). To our knowledge, this the first report of P. pachyrhizi in Mexico. Voucher specimens have been placed in the USDA National Fungus Collection as BPI 871130, BPI 871131, and BPI 871132. Images and a complete description of Asian soybean rust can be viewed at http://nt.arsgrin.gov/taxadescriptions/factsheets/index.cfm?thisapp=Phakopsorapachyr hizi.

References: (1) R. D. Frederick et al. Phytopathology 92:217, 2002. (2) R. W. Schneider et al. Plant Dis. 89:774, 2005.