The promotive effect of N2 fixers, Bacillus circulans and Saccharomyces cerevisiae on the viability of native arbuscular mycorrhizal fungi and the impact on the productivity of alfalfa (Medicago sativa l.)

Abstract

This study was carried out to investigate the effects of inoculation with symbiotic (Rhizobium meloti), Asymbiotic (Azospirillium lipoferum), K- solubilizers (B. circulans) and Saccharomyces cerevisiae (as plant growth promoters) on the viability of native mycorrhizal spores (endogenous) and the increase of its propagula and the impact on growth and productivity of Alfa-Alfa .This study was carried out in field experiment during winter season (2011/2012) at an experimental farm of Giza Research Station, Agriculture Research Center (ARC), Giza, Egypt. These strains were capable of producing hormone like substances and exo- polysaccharides in variable quantities besides the ability of nitrogen fixation by R. meloti and A. lipoferum in their specific media. The obtained results revealed that the populations of Azospirillum spp., B. circulans and S. cerevisiae in the rhizospheric area were higher with the treatment mixture compared to control. The inoculation with these microorganisms led to the increase of native mycorrhizal colonization (%) in rhizospheric area and abundance of mycorrhizal spores in soil in addition the number of nodules in Alfalfa roots. The mixture treatments was still the superior one where it gave the highest enzymes activity represented in Dehydrogenase (μg TPF/g dry soil/day), nitrogenase (μmole C₂H₄/g rhizosphere/h) and acid and alkaline phosphatase (μg/g dry soil). This treatments also indicated the highest values of carbohydrates crude protein and NPK (%) therefore, this treatment recorded the highest dry highest dry weight (ton/fed) as yield parameter during the first and second cuts, respectively. Its values are: 1.35 and 2.55 (ton/fed), respectively, more than the control and other treatments. It was concluded that the inoculation with these beneficial microorganisms enhanced and promoted the other native microorganisms to exist and colonize the rhizospheric area of plants and hence the increase of soil fertility and plant productivity.