Colonization of Plant Growth Promoting Rhizobacteria Pseudomonas sp. and Bacillus sp. in Soybean Rhizosphere

Abstract

Rhizosphere is a portion of soil affected by substances released by roots (root exudates), which are substrates for microbial growth, thereby triggering a competition amongst various microorganisms to colonize the rhizosphere. The survival and colonization of Pseudomonas sp. Crb 17, Crb 64, and Bacillus sp. Cr 76 were tested in the rhizosphere of soybean grow on sterile and non-sterile soil for six weeks. A marker used to monitor the dynamic population of the isolates in the rhizosphere was rifampicin resistance marker. Based on the results obtained, the rhizosphere colonization ability of these three isolates in the sterile soil was not significantly different (α = 0.05) from that in non-sterile soil, although there was a tendency of higher population in sterile soil compared to non-sterile soil. Colonization ability amongst the isolates was also not significantly different (α = 0.05) both in sterile and non-sterile soil. However, in non-sterile soil, colonization ability of isolate Crb 64 was better than that of two isolates. Isolate Crb 64 is the most competitive isolate in colonizing soybean rhizosphere. In general, all isolates have high ability to colonize and survive in the soybean rhizosphere as shown by their high population numbers until the end of the observation period, i.e. around 6 to 7 log cells/g dry soil.