Aecial and Pycnial Stages of Bean Rust in Colorado. H. F. Schwartz, Department of Plant Pathology and Weed Science, Colorado State University, Fort Collins 80523. M. S. McMillan, and M. R. Vaughn. Department of Plant Pathology and Weed Science, Colorado State University, Fort Collins 80523. Plant Dis. 74:80. Accepted for publication 10 September 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0080E.
In early June 1989, pycnia and aecia of bean (Phaseolus vulgaris L.) rust, caused by Uromyces appendiculatus (Pers.) Unger var. appendiculatus (= U. phaseoli (Reben.) Wint.), were observed on volunteer plants of pinto bean cultivars U.I. 114 and U.1. 126 that developed from seed missed during harvest of pinto beans from the same fields in September 1988. The plants were found in four fields of winter wheat planted in September 1988 and in a field of corn planted in May 1989. Bean debris with rust telia was also recovered in June 1989 from the soil surface of two of the winter wheat fields. Mature pycnia (light yellow to yellowish brown raised blisters 3-5 mm in diameter) and aecia (white cups in a circular cluster 2-4 mm in diameter) were present on adaxial and abaxial surfaces, respectively, of unifoliolate leaves. Pycnia and aecia were observed commonly as elliptical masses up to 10 mm long on the lower stem and upper hypocotyl near and below the soil surface, apparently where basidiospore infection occurred during seedling emergence. Within 10-14 days after inoculation, aeciospores (from individual aecial clusters) produced reddish brown uredinia on unifoliolate leaves of U.I. 114 seedlings after incubation in a greenhouse mist chamber for 24 hr at 19 C with low light. This is the first report of rust pycnia and aecia on dry beans in Colorado and may have implications for management strategies for susceptible cultivars and breeding for stable disease resistance.