First Report of Uromyces appendiculatus Pycnia and Aecia on Bean in South Africa. F. H.J. Rijkenberg, Department of Microbiology and Plant Pathology, University of Natal, Pietermaritzbtirg 3200, South Africa. Plant Dis. 78:432. Accepted for publication 8 November 1993. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0432A.
Rust, caused by Uromyces appendiculatus (Pers.:Pers.) Unger, is a destructive, ubiquitous disease of bean (Phaseolus vulgaris L.) in South Africa. In southern Africa, both commercial and subsistence farmers expend considerable effort on breeding bean varieties resislant to rust. Most rusted plants form telia in the fall and winter. Since beans are grown throughout the year in coastal areas of Natal, the uredial stage is always present, and teliospores are not essential to the overwintering of the fungus. To ascertain whether the sexual cycle could function in this region, bean leaves bearing abundant telia were stored under the eaves of a building in an open plastic bag from June to September 1992. During the first week of October 1992, dried leaves were sandwiched between wire netting and suspended over bean plants with the first trifoliate leaf fully expanded (cv. Gellman Runner) planted in open ground in the Pieter-maritzburg area. Plants were exposed to natural rainfall and dew. During the second week of November, abundant pycnia and aecia were observed on the leaves. On 14 November, aecia were pressed against abaxial leaf surfaces of uninfected plants of the same cultivar, and uredinia developed by 3 December, again under natural conditions of rain and dew. The observed sexual stage of the fungus is an indication to breeders and pathologists that the generation of new races is likely to be higher than in the absence of this stage.