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Title: FIRST REPORT OF ASIAN SOYBEAN RUST, PHAKOPSORA PACHYRHIZI, FROM MEXICO

Author
item RODRIGUEZ, A - MEXICO
item RIOS, J - MEXICO
item Hernandez, Jose

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/20/2006
Publication Date: 8/19/2006
Citation: Rodriguez, A.C., Rios, J.A., Hernandez, J. 2006. First report of Asian Soybean Rust caused by Phakopsora Pachyrhizi, from Mexico. Plant Disease. 90:1260.

Interpretive Summary: Soybean rust causes a serious disease of soybean that has been considered a threat to the United States for at least two decades. Once this disease moved from Africa to South America, scientists predicted that soybean rust could be blown northward into the U.S. by hurricane winds. This fungus was discovered in a soybean field in Louisiana in November, 2004 following Hurricane Ivan. Since then, scientists have searched for soybean rust in Central America to determine how widespread is this pathogen. Exploration for rust fungi in Mexico revealed the existence of soybean rust in the northeastern state of San Luís de Potosí. This is along the path predicted for spread of soybean rust and confirms the model pathway. This research will be used to determine the spread of invasive rust fungi and to predict their possible future path.

Technical Abstract: Leaves of soybean (Glycine max (L.) Merr.), Fabaceae, with conspicuous chlorotic spots and associated hypophyllous cinnamon brown sori, were collected in Ébano and Tamuín in the state of San Luís de Potosí, Mexico, on the 26th of 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 were cylindric to clavate, 25-50 × 6-14 µm, colorless to yellow-brownish with wall thickened at the apex. Urediniospores are obovoid to broadly ellipsoidal, measuring 18-37 × 15-24 µm, and with a minutely echinulate thin wall, hyaline to pale yellowish-brown. This morphology is typical of Phakopsora pachyrhizi and P. meibomiae. DNA was extracted from leaves containing sori using the PureLink Plant RNA Reagent (Invitrogen) and by the polymerase chain reaction protocol (1), using Ppa1/Ppa2 primers, the identity of P. pachyrhizi was confirmed by the National Phytosanitary Reference Centre of Mexico. The morphological and molecular diagnosis and presence of P. pachyrhizi in Mexico was officially communicated by North American Plant Protection Organization (NAPPO) on February 16, 2006. Asian soybean rust was reported for the first time in North America in 2004 (2). 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.ars-grin.gov/taxadescriptions/factsheets/index.cfm?thisapp=Phakopsorapachyrhizi.