Bacteria and actinomycetes associated with pot cultures of vesicular–arbuscular mycorrhizas

Abstract

The bacteria and actinomycetes associated with pot cultures of the vesicular-arbuscular (VA) mycorrhizal fungi Glomus fasciculatum, Gigaspora margarita, Acaulospora laevis, Sclerocystis dussii, and of a control without VA mycorrhizal fungus were studied. Total bacterial populations and numbers of nitrogen fixers were significantly higher in the pot cultures of G. fasciculatum, G. margarita, and S. dussii. There were more gram-negative bacteria in these three pot cultures. Spore formers decreased and urea hydrolysers increased in all four pot cultures. The pot cultures of A. laevis harboured fewer bacteria compared with the control. The occurrence of amino acid requiring bacteria increased in all the pot cultures, except that of A. laevis. Pot cultures of G. fasciculatum and A. laevis had significantly more actinomycetes than the control. Streptomyces, series Rectus flexibilis, was selectively stimulated. These two pot cultures also had more actinomycetes antagonistic to the pathogens Fusarium solani and Pseudomonas solanacearum than the control. Glomus margarita pot cultures harboured more actinomycetes antagonistic to the phytopathogenic bacterium Xanthomonas campestris pv. vignicola.