|Du Preez, Eve|
|Van Rij, Neil|
Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2004
Publication Date: 2/1/2005
Citation: Plant Disease 89:206
Interpretive Summary: Soybean rust, caused by the fungus Phakopsora pachyrhizi, is a devastating disease of soybeans and is found worldwide except North America and Europe. In 2001, the disease was discovered for the first time on soybeans in South Africa, and the disease has become endemic. In April 2004, dry beans at the Cedara Agricultural Research Farm in KwaZulu-Natal province in South Africa were found to be infected with common bean rust, Uromyces appendiculatus, and what appeared to be a second rust fungus. Real-time polymerase chain reaction assays and nucleotide sequence analysis confirmed Phakopsora pachyrhizi infection of dry beans. Since dry beans are grown year-round in frost-free areas in South Africa, they may serve as an important over-wintering host and source of the rust spores for soybean infections.
Technical Abstract: In April 2004, dry bean plants (Phaseolus vulgaris) growing adjacent to rust-infected soybean plants (Glycine max) at Cedara Agricultural Research Farm (29°32'S 30°16'E), were found to be infected with two distinct types of rust. The common bean rust (Uromyces appendiculatus), with reddish-brown uredinia and black telia, was readily identified. A second rust, with smaller sporulating uredinia, which were greyish in appearance, was also found. Microscopic examination of the urediniospores from the smaller lesions revealed that they were morphologically similar to Phakopsora pachyrhizi. Real-time fluorescent polymerase chain reaction assays and sequence analysis of the internal transcribed spacer region 2 verified the identity of the urediniospores as P. pachyrhizi. Although P. vulgaris is a known host of P. pachyrhizi, it is the first time that the pathogen had been observed on an alternate host plant in South Africa since the arrival of soybean rust in 2001. Since dry beans are grown year-round in frost-free areas, the implications are that dry beans may serve as an important over-wintering host and source of inoculum for seasonal soybean rust infections.