EFFECT OF SOIL-SPRAYING TIME ON ROOT-COLONIZATION ABILITY OF ANTAGONISTIC STREPTOMYCES-GRISEOVIRIDIS

The root-colonization ability of Streptomyces griseoviridis Anderson e t al. was tested on turnip rape (Brassica rapa subsp. oleifera DC.) an d carrot (Daucus carota L.) by the sand-tube method. Nonsterile sand w as sprayed with a microbial suspension immediately or 7 days after the seed had been sown. Results expressed as population frequencies and d ensities indicated that S. griseoviridis effectively colonizes the rhi zosphere when the microbe is applied immediately after sowing but less effectively when it is applied 7 days later. Detection values of S. g riseoviridis were higher for turnip rape than for carrot. In sterile s and, S. griseoviridis invariably colonized the rhizosphere of turnip r ape after each of the two applications. These findings indicate that S . griseoviridis can compete with indigenous soil microbes in the rhizo sphere if it is sufficiently abundant in the soil before the seed emer ges. If applied later, however, it competes rather poorly. In root-fre e nonsterile sand, S. griseoviridis dispersed and survived well.