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United States Department of Agriculture

Agricultural Research Service

Title: First Report of Soybean Rust Caused by Phakopsora Pachyrhizi on Phaseolus Species in the United States

Authors
item Lynch, T - UNIVERSITY OF ILLINOIS
item Marois, J - UNIVERSITY OF FLORIDA
item Wright, D - UNIVERSITY OF FLORIDA
item Harmon, P - UNIVERSITY OF FLORIDA
item Harmon, C - UNIVERSITY OF FLORIDA
item Miles, Monte
item Hartman, Glen

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 15, 2005
Publication Date: January 1, 2006
Citation: Lynch, T.N., Marois, J.J., Wright, D.L., Harmon, P.F., Harmon, C.L., Miles, M.R., Hartman, G.L. 2006. First report of soybean rust caused by Phakopsora pachyrhizi on phaseolus species in the United States. Plant Disease. 90:970.

Interpretive Summary: Phakopsora pachyrhizi, the causal fungus of soybean rust, was first observed in the continental United States in November 2004. During the growing season of 2005, P. pachyrhizi was confirmed on soybean and/or kudzu in nine states in the southern US. On 7 December 2005, leaves of Phaseolus coccineus L. (scarlet runner bean, PI311827), P. lunatus L. (lima bean, PI583558), and two P. vulgaris L. (kidney bean) cultivars (Red Hawk and California Early Light Red Kidney or CELRK) with suspected rust lesions were observed adjacent to a rust-infected soybean field in Quincy, FL. Upon microscopic examination, the leaves from the Phaseolus spp. plants were shown to have rust pustules characteristic of P. pachyrhizi uredinia. Polymerase chain reactions (PCR) using two sets of primers (Ppa1/Ppa2 and Pme1/Pme2) were performed on DNA extracted from leaves of the three species with sporulating rust pustules. The results of these tests confirmed that P. pachyrhizi was the causal organism for the observed rust. This information will be useful for plant diagnosticians, epidemiologists, scientists in the dry bean industry and others interested in soybean rust and its development on other hosts.

Technical Abstract: Phakopsora pachyrhizi Syd. & P. Syd., the cause of soybean rust, was first observed in the continental United States in November 2004 on soybean followed by kudzu. On 7 December 2005, leaves of Phaseolus coccineus L. (scarlet runner bean, PI311827), P. lunatus L. (lima bean, PI583558), and two P. vulgaris L. (kidney bean) cultivars (Red Hawk and California Early Light Red Kidney or CELRK) with suspected rust lesions were observed adjacent to a rust-infected soybean field in Quincy, FL. Upon microscopic examination, the leaves from the Phaseolus spp. plants were shown to have rust pustules characteristic of P. pachyrhizi uredinia. Uredinia were counted within a randomly selected 2-cm square area of one leaf of each sample. The mean and range of uredinia per lesion for P. coccineus was 29 uredinia with a range of 0 to 3 uredinia per lesion; P. lunatus had 2 uredinia with 0 to 1 uredinium per lesion; P. vulgaris Red Hawk had 22 uredinia with 0 to 5 uredinia per lesion; and P. vulgaris CELRK had 43 uredinia with 0 to 4 uredinia per lesion. Polymerase chain reactions (PCR) using two sets of primers (Ppa1/Ppa2 and Pme1/Pme2) were performed on DNA extracted from leaves of the three species with sporulating rust pustules. The results of these tests confirmed that P. pachyrhizi was the causal organism for the observed rust.

Last Modified: 4/19/2014
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