Rhizosphere Microflora and Nodulation of Licorice Plant

Abstract

The effect of cutting root-extracts of licorice plant on certain microorganisms in vitro was studied. On culture media, the antibacterial effect expressed as “width of inhibition zones” differed according to type of microorganisms and method of extraction. In vivo occurrence of certain soil microorganisms in the rhizosphere soil of licorice during different growth phases was also studied. Generally, counts of bacteria (total), sporeformers, actinomycetes, fungi, aerobic nitrogen fixing Azotobacter and of anaerobic nitrogen fixing clostridia, were higher in the rhizosphere soil than in the non-rhizosphere one resulting in positive rhizosphere effects during 120 days after planting. The morphological examination of the isolates from rhizosphere and non-rhizosphere soil showed that there was a marked predominance of Gram-negative types in the rhizosphere soil of licorice; the incidence of Gram-positive types were higher in the control non-rhizosphere one. Number of nodules ranges from 7–10 per plant. Re-inoculation of locorice plant with effective nodule bacteria isolated from locorice plant increased densities of nodules. Cross-inoculation investigation showed that root nodules bacteria isolated from licorice plant formed nodules only on the roots of broad bean (Vicia faba) and vice versa.