Metabolites fromPseudomonas fluorescensStrain D7 Inhibit Downy Brome (Bromus tectorum) Seedling Growth

Abstract

Phytotoxins produced by the naturally-occurring rhizobacterium,Pseudomonas fluorescensstrain D7 (strain D7), in shake cultures from several media sources adversely affected downy brome at several growth stages and affected seeds, whole plants, and isolated cells. These uncharacterized phytotoxins inhibited root and shoot growth of downy brome by 80% in a seed germination agar assay at 2 and 400 ng total solids/ml, respectively. In a hydroponics assay, downy brome and winter wheat dry weights were reduced 50% by cell-free broth concentrations of 15 and 26% of the initial broth concentration, respectively, indicating an almost 2x selectivity between winter wheat and downy brome. Plant water use was reduced similarly. Plasma membranes of isolated protoplasts of downy brome were damaged within 2 h by diluted cell-free broth. Cold-precipitated phytotoxins of strain D7 produced in semi-synthetic and synthetic media reduced dry weight of downy brome seedlings by 100 and 89%, respectively, and killed plants rapidly.

Controlling weeds with fungi, bacteria and viruses: a review

“…Pseudomonas fluorescens strain D7, originally isolated from the rhizospheres of winter wheat ( Triticum aestivum ) and downy brome ( Bromus tectorum ) in Western Canada, has been observed to selectively inhibit growth and germination of a number of grassy weeds, most notably downy brome ( Kennedy et al, 1991 , 2001 ; Gealy et al, 1996 ). By selective removal of compounds from cell-free filtrates, the growth-inhibiting activity associated with this strain was attributed to a combination of extracellular peptides and a lipopolysaccharide, which were suggested to work in conjunction to express herbicidal activity ( Gurusiddaiah et al, 1994 ).…”

Bioherbicidal potential of a strain ofXanthomonasspp. for control of common cocklebur (Xanthium strumarium)

“…A granular formulation containing P. fluorescens cells was evaluated as a soil-applied bioherbicide for green foxtail (Setaria viridis L.) control (Caldwell, Hynes, Boyetchko, and Korber 2012). Phytotoxins of certain P. fluorescens (Gurusiddaiah, Gealy, Kennedy, and Ogg 1994) and Pseudomonas syringae strains (Gealy, Gurusiddaiah, Ogg, and Kennedy 1995;Gealy, Gurusiddaiah, and Ogg 1996) inhibited the germination and early root growth of downy brome (Bromus tectorum). Bacterial strains of various Xanthomonas spp.…”

Application Potentials of Plant Growth Promoting Rhizobacteria and Fungi as an Alternative to Conventional Weed Control Methods

“…Two major classes of rhizobacteria that show herbicidal activity are Pseudomonas and Xanthomonas sp. Different rhizobacterial species have been investigated as weed control agents on different crops based on their secondary metabolites [115,116]. As stated earlier Pseudomonas have gained much importance as an agent in biological weed management; there are many strains of this genera, some are plant beneficial [117] and others can have inhibitory effects on plants [118] and so can be applied in biological weed control.…”

“…A strain of Pseudomonas fluorescens (D7) isolated from wheat and downy brome rhizosphere has shown inhibitory effects on a number of grassy weeds especially downy brome by virtue of production of a phytotoxin [116,119,121]. Kremer et al [122] tested the phytopathogenic ability of different fluorescent and nonfluorescent pseudomonads which were isolated from the rhizosphere of seven important weeds.…”