Submitted to: Symbiosis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/13/2001
Publication Date: 1/1/2002
Citation: LI, J., KREMER, R.J., ROSS, J.L. ELECTRON MICROSCOPY OF ROOT COLONIZATION OF SETARIA VIRIDIS BY DELETERIOUS RHIZOBACTERIA AS AFFECTED BY SOIL PROPERTIES. SYMBIOSIS. 2002. V. 32. P. 1-14.
Interpretive Summary: Plant roots provide unique environments for microorganisms whose various activities can have either a beneficial or detrimental effect on plant growth. We identified bacteria inhabiting roots (rhizobacteria) of weeds in crop fields that suppressed the growth of the weeds. We then added the rhizobacteria to soils from different cropping systems to see if they would dsuppress weed (green foxtail) growth under various soil environmental and management conditions. We found that all rhizobacteria strains suppressed green foxtail growth when added to soil from an organic farm that had high organic matter content and near neutral pH. Some strains did not suppress green foxtail growth in soils of low organic matter and more acid pH. Microscopic observation at very high magnification (5,000 to 10,000 times) revealed dense populations of the rhizobacteria strains attached to green foxtail root surfaces indicating that intense root colonization leads to growth suppression. Results are important to scientists and producers because they illustrate that management practices that maintain or improve soil organic matter content are most likely to enhance indigenous weed growth-suppressive rhizobacteria and promote rapid establishment and activity of potential weed biocontrol rhizobacteria introduced into soil.
Technical Abstract: Root colonization of green foxtail (Setaria viridis) seedlings grown in three different soils inoculated with selected deleterious rhizobacteria (DRB) was studied using scanning electron microscopy. The three DRB originated from Setaria faberi seedlings growing in soils under different management and with different organic matter and pH. The DRB strains reduced green foxtail seedling growth > 50% in agar bioassays. Electron microscopic observations revealed the DRB strains preferentially colonized root surface crevices over ridges. Each strain densely colonized roots of green foxtail when inoculated in its native soil, probably due to adaptation to the particular chemical, physical, and biological properties embodied by each soil. Bacterial colonization and establishment on seedling roots led to growth inhibition. Pseudomonas fluorescens strain L2-19 and Stenotrophomonas maltophilia strain TFR1 significantly reduced green foxtail growth in all three soils; however, P. putida strain B1-7 inhibite green foxtail only in the high organic matter, high pH soil under an organic farming management system. All three strains significantly inhibited green foxtail shoot growth in the organically managed soil, indicating that organic matter content is an important factor affecting growth suppressive activity of DRB. In general, seedlings grown in an uncultivated prairie soil with high organic matter and low pH produced less biomass than those grown in other soils. This suggests that soil pH also may be involved in the growth suppression of host plants by DRB.