Pengaruh Hormon Asam Indol Asetat yang Dihasilkan Azospirillum sp. terhadap Perkembangan Akar Padi

Abstract

Free-living bacteria of the genus Azospirillum live in close association with rice roots. This bacteria produced indole acetic acid (IAA), a plant growth hormon, to the environment. IAA was isolated from cultures of Azospirillum strains and investigated for its effect on root development and plant height of rice variety IR64 in vitro. Rice cultures of variety IR64 were grown in vitro and inoculated with cultures of Azospirilllum. Production of IAA by the bacterium during its growth period in rice culture medium containing different levels of nitrogen was observed. Results of the experiment showed that strains Azospirillum Az15 and Az44 had a high ability to produce IAA, i.e., 57.93 μg/ml at 12 days after incubation (DAI) and 40.42 μg/ml at 7 DAI, respectively. The IAA production pattern of Azospirillum Az15 and Az44 in the liquid medium were fluctuative until the end of the incubation period, while that of the strain Az7 was linier. Strain Az7 gave a better effect on the root development and plant height than strains Az15 and Az44. Treatment combination of strain Az7 and 100% nitrogen gave highest root development. High level of nitrogen increased IAA content in the uninoculated culture, while low IAA content on the inoculated one. Inoculation the culture with strain Az7 together with 50% nitrogen application resulted in the IAA content, root dry weight, root length, fiber root number, and plant height as high as those on cultures containing 100% nitrogen (1 mM NH4NO3) without inoculation. Inoculation of rice culture with Azospirillum is expected to reduce nitrogen application on rice IR64 by the IAA production as indicated by significant changes in the root growth and development. A higher concentrations of IAA tend to give better effects on the root growth and development of rice IR64.