Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2000
Publication Date: 3/4/2001
Citation: Kennedy, A.C., Johnson, B.N., Stubbs, T.L. 2001. Host range of a deleterious rhizobacterium for biological control of downy brome. Weed Science. Interpretive Summary: In the United States, the weed downy brome (Bromus tectorum L.) and related Bromus species infest an estimated 14 million acres of dryland winter wheat. This weed reduces wheat yields by an estimated 15% or $300 million annually. Biological control has the potential to be used as an alternative method of control. Preliminary research has shown that weed-suppressive bacteria selectively inhibit the weed up to 50% in winter wheat fields. Before commercialization as a biological control agent, the bacteria must be tested for activity on other plants. Our objective was to determine the effect of the bacteria on the growth of many different agronomic crops, rangeland forage grasses, commercial turfgrasses, or weeds. We found that the root-suppression was specific to the weed downy brome or related plant species. Other species were not inhibited by the weed-suppressive bacteria. The use of these biological control agents would impart little ecological risk to the other plants. This study helps to implement a novel, and safe biological weed control technology that should significantly reduce costs and the need for tillage and chemical herbicides to control grass weeds in small grain crops. Besides lower input costs, the biological control technology should help farmers to reduce erosion and water pollution by enabling them to use more sustainable practices and conservation cropping systems that are both profitable and ecologically sound.
Technical Abstract: Pseudomonas fluorescens strain D7 is a root-colonizing bacterium that inhibits downy brome (Bromus tectorum) growth. In advance of commercialization as a biological control agent, strain D7 must be tested for host plant specificity. Agar plate bioassays in the laboratory and plant-soil bioassays in a growth chamber were used to determine the influence of P. f. D7 on 45 select plant species common in the western United States. In the agar plate bioassay, supernatant of the bacterium reduced root length of dicotyledonous seedlings by 15% compared to control roots, while those of non-Bromus monocots were reduced up to 76%. Root growth of seven Bromus spp. were inhibited an average of 80%. In plant-soil bioassays, root inhibition by the bacterium was less than that observed in agar plates, and in some cases, the bacterium increased root growth. Among all plant species, the bacterium inhibited downy brome to the greatest extent (42% root reduction). The root-suppressive capability of P. f. D7 was specific to Bromus spp., particularly in soil-grown plants.