AbstractSystemic acquired resistance (SAR) and microbial biocontrol each hold promise as alternatives to pesticides for control of plant diseases. SAR andBacillus cereusUW85, a microbial biocontrol agent, separately suppress seedling damping‐off diseases caused by oomycete pathogens. The purposes of this study were to investigate how expression of SAR affected the efficacy of biocontrol by UW85 and if UW85 treatment of plants induced SAR. We devised a laboratory assay in which seedling damping‐off disease, induction of SAR, and growth of UW85 could be quantified. Seedlings ofNicotiana tabacumXanthi nc were germinated on moist filter paper and transferred after 7 days to water agar plates (40 seedlings per plate). Zoospores of oomycete pathogens (Pythium torulosum, Pythium aphanidermatum, orPhytophthora parasitica) were applied at concentrations that caused 80% seedling mortality within 10 days. Seedling mortality was dependent on zoospore inoculum concentration. The level of disease suppression caused by treatment with UW85 depended on the UW85 dose applied. SAR was induced with 0.5‐mM salicylic acid or 0.1‐mM 2,6‐dichloroisonicotinic acid. Expression of an SAR‐related gene was confirmed by northern analysis with a probe prepared from a tobacco PR‐1a cDNA. Induction of SAR suppressed disease caused by each of the oomycete pathogens, but did not alter the growth of UW85 on roots. Treatment of seedlings with UW85 did not induce the expression of PR‐1a. The combination of induction of SAR and treatment with UW85 resulted in additive suppression of disease as measured by se