Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/1998
Publication Date: N/A
Interpretive Summary: Birdsfoot trefoil, a highly palatable forage for dairy and beef production, is often difficult to establish due to susceptibility to various soilborne diseases that decrease vigor and cause poor seedling emergence. Thus, we were interested in surveying bacteria intimately associated with birdsfoot trefoil seedling roots to see if these organisms were involved in causing disease along with the suspected disease agents. We looked for bacteria that were able to specifically travel to birdsfoot trefoil seeds in soil. Several bacteria were able to go toward certain chemicals or nutrients leaking from seeds and roots, multiply in population, and harm birdsfoot trefoil by reducing growth. The results showed that bacteria were involved in damaging the plant root and indicated some diseases of birdsfoot trefoil may be more complicated than expected since more than one causal agent is involved. This information is important to plant breeders, forage scientists, and farmers because varieties and management practices can be developed to resist or tolerate the numerous organisms involved in seedling diseases, leading to improved and long-lasting stands of birdsfoot trefoil for efficient beef and dairy production.
Technical Abstract: Intact seeds and seed and seedling root exudates of birdsfoot trefoil (Lotus corniculatus L.) were used as chemoattractants in experiments to determine the relative importance of chemotaxis in spermosphere and rhizosphere colonization by selected rhizobacteria. Results for soft-agar, capillary tube, and soil chemotaxis assays indicated that selected deleterious rhizobacteria were specifically attracted to seed and seedling root exudates. Several sugars and phenolic fractions detected in exudates were chemoattractants for these rhizobacteria. Using soil-chemotaxis assemblies, migration of rhizobacterial isolates through 2-cm distances of soil toward birdsfoot trefoil seeds was detected within 24 h. Isolates were not detected at the same site in soils without seeds until 72 h after inoculation. These results suggest that attraction of deleterious rhizobacteria toward seeds and seedling roots mediated by exudates (chemotaxis) might be the first step in establishment and subsequent colonization of bacteria involved in soilborne disease complexes of birdsfoot trefoil.