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-degrees-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-degrees-C than at 18/13 and 25/15-degrees-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-degrees-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.