Suppression of Downy Brome Growth by a Rhizobacterium in Controlled Environments

Plant‐suppressive rhizobacteria have the potential to be used as biological control agents to combat weeds. Pseudomonas fluorescens strain D7 (D7) was introduced to downy brome ( Bromus tectorum L.) seeds to determine the importance of soil water content and temperature on plant suppression in controlled environments. Downy brome seeds were inoculated with a spontaneous rifampicin‐resistant mutant of D7 (D7rif) and grown for 14 d at light/dark temperatures ranging from 10/10 to 25/15 °C. In another study, downy brome seeds were inoculated with D7rif in soil at −1.0, −0.1, and −0.03 MPa water pressure. Root colonization by the introduced bacterium was greater at light/dark temperatures of 10/10 °C than at 18/13 and 25/15 °C. Apical root colonization was limited in dry soil. Strain D7rif suppressed downy brome growth in all treatments, but the extent of suppression varied. Greatest suppression occurred in cool (10/10 or 18/13 °C) or moist (−0.03 MPa) conditions. Like many annual weeds, downy brome seeds germinate and establish in the cool, wet autumn; thus, autumn applications of the bacterium may result in a significant biocontrol benefit.