In February 2001, soybean rust caused by Phakopsora pachyrhizi Syd. was detected for the first time on soybean (Glycine max) near Vryheid in northern KwaZulu-Natal, South Africa (previous news story 03/26/01). As the season progressed, the disease was also observed in other parts of the province, and epidemic levels were reached in the Karkloof, Cedara, Howick, and Greytown production regions.
To confirm pathogenicity, 10 to 15 plants of each of the South African soybean cvs. Pan 589, Pan 780, Pan 854, Octa, and Prima were inoculated with isolate PREM 57280. Primary leaves were sprayed with a suspension of spores in light mineral oil ([ca] 1 mg of spores per ml) before incubating plants in the dark in a dew chamber for 16 h. Large, sporulating uredinia, producing typical soybean rust urediniospores, developed on all inoculated plants.
Classical and real-time fluorescent [PCR] assays as well as sequence analysis of the internal transcribed spacer regions verified that isolate PREM 57280 was P. pachyrhizi. Since the disease is known to occur in Zimbabwe, Mozambique, and several other African countries, inoculum was most likely introduced by air currents from countries to the north of South Africa. It is considered probable that soybean rust will successfully overwinter in South Africa based on experience in other southern African countries.