Abstract

Strains of the genera Nostoc (7 species) and Phormidium (one species) were isolated from soil. Cyanobacterial isolates were tested for their ability to form associations with the roots of wheat seedlings grown in liquid culture as well as fixing of atomospheric N₂. The present study revealed that Nostoc colonization of wheat was tight association whilephormidium colonization was loose association. In case of Nostoc association, its growth was in the form of aseriate packages on root surface. Moreover, our study reported thatNostoc muscorum isolate No. (12) had the ability to penetrate epidermal cells. In microcosms experiment, cyanobacterial isolates positively affected wheat growth as compared to the non-heterocystous isolate, Phormidium. Nostoc rivulare and Nostoc muscorum isolate No. (12) were more efficient in nitrogen fixing activity as compared to the rest of isolates. In case of 2,4-dichlorophenoxyacetic acid induced maize roots, nitrogenase activity of Nostoc significantly enhanced as compared to the untreated maize roots. Nostoc muscorum or Nostoc rivulare colonized externally at the junction of the para-nodules, and also abundance of Nostoc on the induced maize roots increased as compared to the untreated maize roots. Nitrogenase activity and abundance of Nostoc muscorum or Nostoc rivulare co-cultivated with maize roots was increased up to 1.7 times in the absence of combined nitrogen (nitrates) as compared to the nitrate treated plants. In pot experiments, biofertilization by Nostoc muscorum or Nostoc rivularesignificantly increased shoot length and leaf area of maize either alone or in combination with N-fertilizer at 50 and 100 kg N/ha. Combination of biofertilization and N-fertilization, especially at 100 kg N/ha had more effect on the growth of maize compared to the biofertilization alone, as well as nitrogenase activity.

Key words: Cyanobacteria, maize, biofertilization, ammonium sulphate.