Growth-promotingazospirillumspp. isolated from the roots of several non-gramineous crops in Japan

Abstract

Nitrogen-fixing bacteria were isolated from the roots of five non-gramineous crops (Spinacia oleracea, Brassica chinensis, Brassica rapa var. pervidis, Glycine max, Cucumis sativus) grown on soils from Tsukuba and Kukizaki, Ibaraki, Japan. All the isolates were assumed to be Azospirillum brasilense- like bacteria. These isolates were unable to utilize glucose as the sole carbon source and exhibited nitrate reductase (Nr) and nitrite reductase (Nir) activities, except for the isolates from soybean roots which did not display any Nir activity. Acetylene reduction activities (ARA) of all the isolates were lower than that of the type culture of A. hrasilense. Some of the isolates exerted a growth-promoting effect on the roots and shoots of their respective host plants by inoculation to the roots. Dual inoculation of Bradyrhizobium and Azospirillum, spp. isolated from soybean roots inhibited the nodulation and ARA.