Abstract

Using sonication technique and addition of 2,4 dichlorophenoxyacetic acid to wheat roots, increasing colonization of Nostoc muscorum on roots and enhancement of nitrogen fixation as novel associations between nitrogen fixing Nostoc muscorum and nonlegume wheat, had been occurred. Sonication of roots (10 and 20 s) enhanced abundance of N. muscorum within / on the root tissue.The N. muscorum penetrated the roots in the form of motile filaments (hormogonia) and once inside, they divided and transformed into aseriate packages. Sonication technique does not have significant effect on root growth, and there are no significant differences in shoot growth. Treatment of wheat roots with low concentrations of 2,4 dichlorophenoxyacetic acid (0.5, 1.0 and 3.0 ppm) developed nodule like structures (para-nodules) mainly along primary roots. N. muscorum colonized the paranodules externally at the junction of the paranodules. Addition of 2,4 dichlorophenoxyacetic acid significantly enhanced the rate of acetylene reduction of inoculated plants, and also abundance of N. muscorum on 2,4 dichlorophenoxyacetic acid induced wheat root compared to untreated wheat roots. Reduction of the growth of both root and shoot occured at a tested concentrations of 2,4 dichlorophenoxyacetic acid. Nitrogenase activity of N. muscorum co-cultivated with wheat roots was increased up to 1.9 times in the absence of combined nitrogen (nitrates) compared with nitrate treated plants, and also abundance of N. muscorum on roots increased in absence of combined nitrogen (nitrates). Results of this study revealed that N. muscorum is a promising organism for achieving efficient association between N₂ fixing cyanobacteria and nonlegumes by using sonication technique or 2,4 dichlorophenoxyacetic acid at low concentrations.

Key words: Nostoc muscorum, sonication, 2,4 dichlorophenoxyacetic acid (2,4-D), nonlegume.