Primary Studies On Rhizobia Isolated From Root Nodules Of Acacia Crassicapa And Acacia Cincinnata

Physiological and biochemical characteristics, adaptations to growth environment, inoculation in test tubes and potted seedlings, and identification of the central strains of the twenty-one rhizobial strains which isolated from root nodules of Acacia crassicapa and Acacia cincinnata were studied in this paper.According to tests of colony formation days on plate and generation time determination, all strains were primary clustered into two groups: one is fast-growing rhizobium, the other is slow-growing rhizobium. The results showed that these strains varied in colony morphologies, growth rates, physiological and biochemical characteristics of rhizobia. The optimum growth temperature of these strains was at 28℃. All strains grew with initial PH from 5.5 to 7.5 and were tolerant to salt on medium containing 0.5 % NaCl. Significant differences in antibiotic susceptibility were seen among these strains. A strain named H004 was selected with good tolerance to high temperature, acid, salt and antibiotics.Acacia crassicapa seedlings inoculated with 21 rhizobial strains in test tubes and back-inoculated with 9 rhizobial strains in soil pots, respectively. The results indicated that inoculation with rhizobia significantly stimulated the growth and nitrogen fixation ability of host seedlings. In the test-tubes experiences, nitrogenase activity, mean nodule weight per seedling, mean nodule number per seedling and nodulation rate were different and have no significant correlation with original hosts. The strains named H009, H008, J012 and J006 were screened primarily as efficient symbiotic nodulation occupancy ability. In the soil-pot experiences, according to the effects of inoculation to height, diameter and total biomass of Acacia Crassicarpa seedlings, the strains named H006 and H007 were screened primarily as efficient strains.Combining morphological, biochemical and physiological characteristics with 16S rDNA sequence analysis, strain named H006 should belong to Rhizobium, and strain named J006 should belong to Mesorhizobium.