Nodule-like Structures Induced on the Roots of Maize Seedlings by the Addition of Synthetic Auxin 2,4-D and its Effects on Growth and Yield

Abstract

Induction of para-nodules on maize contributed to increase in yield. The nodules on maize (Zea mays L.) cv. Kiran were induced using plant growth regulator 2,4-D (lppm) in nitrogen free Hoagland solution. Concentrations of 2,4-D greater than lppm caused stunting and death, while concentrations less than lppm has no obvious effect on seedling growth. The associative symbiosis (using Azospirillum) was noticed in the nodulated and non-nodulated maize plants. The presence of nitrogenase activity (acetylene reduction assay) and leghemoglobin was noticed in the plants treated with Azospirillum either alone or with nodulated plants, but higher activity was noticed in the nodulated Azospirillum treated plants. The 2,4-D induced nodule like structures provided niche for the establishment of the bacteria, thereby enhancing nitrogen fixation in the nodulated roots. These results confirmed the nitrogenase activity of Azospirillum brasilense in association with the 2,4-D induced nodules of maize. After transplanting in the pots, it was noticed that nodulated and Azospirillum treated plants showed higher chlorophyll content in leaf, enhanced NR activity leading to higher yield as compared to controlled plants (non-nodulated). The nodulated plants treated with Azospirillum had higher physiological activities as compared to only Azospirillum treated plants. Thus, the gramineous plants are potentially able to create a symbiosis with diazotropic bacteria, which colonize para-nodule tissue intracellularly, promoting a higher level of N2 fixation for the better growth and development of the plants.