Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/14/2000
Publication Date: 12/1/2000
Citation: Li, J., Kremer, R.J. 2000. Rhizobacteria associated with weed seedlings in different cropping systems. Weed Science. 48(12):734-741.
Interpretive Summary: Extreme disruptions to the soil environment such as tillage and the addition of chemicals can alter the make-up of soil microbial communities as well as their effects on plants. We collected bacteria inhabiting roots (rhizobacteria) of weeds growing in fields subjected to different types of practices used in producing crops to see if certain management techniques might promote rhizobacteria that slow or suppress the growth of weeds that compete with crops. Soil bacteria from an uncultivated prairie in native grasses were included as controls. We found that weed seedlings from fields under management practices that included a sequence of different crops growing in a recurring succession (crop rotation), minimal use of chemicals such as herbicides and fertilizers, application of organic materials like composts, or minimum tillage possessed the high numbers of rhizobacteria able to suppress weed growth. This was similar to the undisturbed prairie in which the highest proportion of weed-suppressive rhizobacteria was detected. Practices involving yearly cultivation of the same crop, use of high amounts of chemicals, and low organic matter in soil contributed to low levels of weed-suppressive rhizobacteria. Results are important to scientists, producers, and extension personnel because certain crop management practices that already sustain our soil resource might be exploited further developing weed-suppressive soils based on promotion of certain bacteria on weed roots.
Technical Abstract: Rhizobacteria isolated from the rhizospheres of dominant weed species in representative cropping systems in mid-Missouri were screened for phytotoxicity on lettuce seedlings and host plants. The frequency of deleterious rhizobacteria (DRB) among different cropping systems was determined. Phytotoxicity screening on lettuce seedlings revealed that an integrated crop management system with a corn-soybean-wheat-cover crop rotation under no-tillage had the highest proportion of DRB at 25.3%, followed by an organic farming system with continuous strawberry and organic amendments under minimum tillage at 22.9%. A continuous cool-season grass-legume meadow with no agrochemical inputs had the lowest proportion of DRB at 13%. Crop management practices that maintained high soil organic matter had high proportions of DRB. Phytotoxicity screening on host plants greatly reduced the proportion of rhizobacteria characterized as DRB. Although screening on lettuce is an effective method to detect phytotoxic rhizobacteria, our research indicates that it is essential to test selected cultures on their host weed species for accurate detection. Using this approach, we found that different crop management influences the occurrence of DRB naturally associated with weed seedlings. Results suggest that crop production systems can be developed to favor soil microorganisms such as DRB that naturally suppress weed growth.