Suppression of Cottony Leak of Cucumber with Bacillus cereus Strain UW85. K. P. Smith, Graduate Student, Department of Horticulture, University of Wisconsin, Madison 53706. M. J. Havey, and J. Handelsman. Research Geneticist, Agricultural Research Service, USDA, Department of Horticulture, and Associate Professor, Department of Plant Pathology, University of Wisconsin, Madison 53706. Plant Dis. 77:139-142. Accepted for publication 7 September 1992. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1993. DOI: 10.1094/PD-77-0139.

Bacillus cereus strain UW85 was previously shown to suppress seedling diseases caused by oomycetous fungi. In this study, we tested UW85 for suppression of cucumber fruit rot caused by Pythium aphanidermatum. To evaluate UW85, we developed an assay for rotting of cucumber fruits by P. aphanidermatum. Wounded fruits were each inoculated with a suspension containing 500 zoospores of the pathogen and incubated at 32 C for 48 hr. Undiluted culture of UW85, containing approximately 4.4 × 10⁸ cells per milliliter, applied to fruit by one of three methods prior to inoculation with the pathogen, significantly reduced rotting (P < 0.05) compared with fruit treated with uninoculated medium or water prior to inoculation with P. aphanidermatum. Culture filtrates and suspensions of UW85 containing less than 1.1 × 10⁸ cells per milliliter did not suppress fruit rotting. UW85 cells that were washed and resuspended in sterile medium did suppress rotting.