English

Abstract

The association of Cymbopogon winterianus (Citronella), a member of the Poaceae family, with the N2-fixing bacteria, Azospirillum was examined to evaluate possible benefits for agriculture. The nodules on citronella were induced using plant growth regulator 2,4-dichlorophenoxyacetic acid (2,4-D) 1.0 ppm in nitrogen free Hoagland’s solution. Concentration of 2,4-D greater than 1.0 ppm caused stunning and death, while concentration of 2,4-D less than 1.0 ppm has no obvious effect on seedling growth. The presence of nitrogenase activity (acetylene reduction assay) and leghemoglobin (hemoprotein found in the nitrogen-fixing root nodules) was noticed in the plants treated with Azospirillum either alone or with nodulated plants, but higher activity was noticed in nodulated Azospirillum treated plants. These results confirmed the nitrogenase activity of Azospirillum brasilense in association with 2,4-D induced nodules of citronella. After transplanting to pots, it was noticed that nodulated and Azospirillum - treated plants showed higher chlorophyll content in leaf, enhanced nitrate reductase (NR) activity, leading to higher yield as compared to the control plants (non-nodulated). The nodulated plants treated with Azospirillum also had higher physiological activities as compared to plants treated only with Azospirillum. The results provide evidence that the plants belonging to the family Poaceae are potentially able to create a symbiosis with diazotropic bacteria, which colonize para-nodule tissue intracellularly, promoting a higher level of nitrogen (N2) fixation leading to better growth and plant development.   Key words: Cymbopogon, nodulation, 2,4-D, Azospirillum brasilense, nitrogen fixation, oil yield.