Screening of Diazotrophs as Plant Growth Promoters and Their Effect in the Development of Maize Seed

Free-living diazotrophs play an important role as plant growth promoters by supplementing nitrogen to deficient soils. In this study, six diazotrophic isolates were selected from 36 previously screened diazotrophic isolates for their mode of action to promote plant growth. A nitrogen free medium was used to screen nitrogen fixing diazotrophs. All strains have exhibited some activity of indole-3-acetic acid production. Strain MAF7-1 shown the highest (0.448 mg ml-1), while strain NUL3-2 exhibited the least (0.032 mg ml-1) production of IAA. Though all isolates were unable to solubilize inorganic phosphate, were able to inhibit the growth of Fusarium oxysporum that causes wilting to plants. There was no significant difference in maize seed germination vigour and rate. However, MAF7-1 had better germination rate and seed vigour (27.5%) when compared to the control (16%). Except strain NUL3-2, all showed significant increase of root length and dry weight of maize seedlings. Therefore, the choice of strain to be used for production of biofertilizer should not only be based on the nitrogenase activity, but also on ability to produce phytohormones. Strain NUL3-2, MAF7-1 and MAF7-3 are potential strains that can be used in the production of biofertilizer. Further study of these strains in depth as plant growth agents and biofertilizer is commendable for future application.