Isolation And Identification Of Several Strains Of Nitrogen-fixing Bacteria In Lesotho And Its Impact On Plant Growth

Growing concerns about the environment, energy, nutrition, and agricultural sustainability make the need for biological nitrogen fixation research even more compelling. Nitrogen fixing bacteria besides fixing nitrogen, they are also able to promote plant growth through other mechanisms including production of hormones, solubilization of phosphorus.In this study,36 diazotrophs were isolated from six different parts of Lesotho's soil which pH range was 6.13-7.22. These diazotrophs were isolated by using free nitrogen medium. After morphological and biochemical tests; they were classified in to six groups. Then one representative was selected from each group to perform further studies.16S rDNA was done for the identification; it was found that PEK1-1, MAF7-3 and NUL3-2 belong to Azospirillum species, PEK1-1 and Azospirillum sp (FN293046), MAF7-3 and Azospirillum sp (X92464); and NUL3-2 and Azospirillum sp TS11 (AB114192) were similar. MAF7-1 and NUL18-1 belong to Azotobacter species. There was similarity between MAF 7-1 and Azotobacter beijerinckii G7 (AB429527) and also between NUL18-1 and Azotobacter beijerinckii ICMP 8673 (EF100151) and Azotobacter beijerinckii ICMP 4032 (EF100152). PEK5-1 belongs to Bacillus species; it is similar to Bacillus sp TW1 (GU905015). The isolated strains were free-living and aerobic diazotrophs.Nitrogenase activity of the six diazotrophs was tested, and there was a significant difference between their nitrogenase activities, the concentration of C2H4 range was 97.01～190.20nmol/mL·h. The nitrogenase activity of NUL3-2 was the highest and the smallest was that of PEK5-1.The strains were tested for their ability to produce Indole Acetic Acid (IAA) and all the strains had positive results, MAF7-1 being the one that produced a great amount of IAA and NUL3-2 produced the least amount (0.448mg/ml and 0.032mg/ml respectively). All isolates were unable to solubilize inorganic phosphate. The strains were able to inhibit the growth of Fusarium oxysporum, pathogenic fungus that causes wilting to the plants.There was no significant difference for germination energy and germination rate. However, MAF7-1 had the better germination energy (27.5%) when compared with the control (16%). All the strains, except NUL3-2, showed a positive influence on the root length and dry weight of maize seedlings. MAF7-1 and MAF7-3 resulted in a very significant increase in roots development compared to control (154% and 128% respectively), MAF7-1 and MAF7-3 gave significant increase in dry weight (425% and 474% respectively). PEK1-1, Azotobacter chroococcum, MAF7-land MAF7-3 had a positive influence on germination index and vigor index. When comparing the diazotrophs from Lesotho and those from China, there was no significant difference.The results showed that there is no relationship between nitrogenase activity and the ability to promote plant growth. NUL3-2, which showed highest nitrogen activity, did not have positive influence on the germination of maize seeds.NUL3-2 was found to be the best to be used for further studies on nitrogen biofertilisers; while MAF7-1 and MAF7-3 can be used for plant growth promoting biofertilisers in Lesotho.