Volunteer Beans with Rust and White Mold Inocula in Winter Wheat. H. F. Schwartz, Department of Plant Pathology and Weed Science, Colorado State University, Fort Collins 80523. M. S. McMillan, and G. K. Lancaster, Department of Plant Pathology and Weed Science, Colorado State University, Fort Collins 80523. Plant Dis. 78:1216. Accepted for publication 3 August 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-1216A.
On 24 May and 6-8 June 1994, pycnia, aecia, and uredinia of Uromy-ces appendiculatus (Pers.) Unger var. appendiculatus were observed on volunteer bean (Phaseolus vulgaris L.) plants of pinto cultivars U.I. 114, Othello, and Bill Z. These volunteers germinated in winter wheat fields at four sites in northeastern Colorado and one site in southwestern Nebraska during May and June from seed unharvested in September 1993. This is the first report of rust pycnia and aecia in Nebraska; and to the previous report (1) in Colorado, pinto cultivars Othello and Bill Z are added. Development of sexual stages on more diverse genotypes could promote more pathogenic variability and threaten the stability of old and new sources of host resistance. Volunteer bean incidence was less than one per 1,000 m2 in harvested bean fields irrigated before being cultivated and planted to winter wheat. However, 1-8 volunteers per 100 m were found in minimum-till chisel-planted schemes that did not incorporate rusted bean debris and/or pregerminate residual bean seed in the previous fall. Apothecia of Sclerotinia sclerotiorum (Lib.) de Bary were observed on moist soil beneath dense canopies of irrigated winter wheat fields in two sites in northeastern Colorado and one site in southwestern Nebraska during early June. Apothecia developed from overwintered sclerotia lying on the soil surface or embedded within previously infected bean debris on the soil surface. Apothecial incidence varied from one to more than 100 per square meter, and ascospore puffing was observed. Although apothecia occur in nonhost crops, this is the first report of their occurrence in winter wheat crops in either state. This inoculum source could explain reports of early-season infection before apothecia appear in downwind fields of susceptible hosts.References: (1) H. F. Schwartz el al. Plant Dis. 74:80, 1990.