2006 Volume 20 Issue 2 Pages 23-29
In previous paper we reported that Streptomyces sp. strain MBR-52 had a potential to accelerate rooting of cucumber seedlings and tissue-cultured seedlings of rhododendron. The carrier of this strain for soil application is one of the key factors for successful agricultural use. For such a practical purpose, organic carriers such as cereal bran, sawdust, and a variety of polysaccharides are routinely used. However, they often cause undesirable adverse effects on plant growth. Thus, the ceramic bead was preferentially selected as a carrier candidate in this paper. MBR-52 successfully attached the beads when they were immersed in mycelial suspension of this strain in culture medium, followed by air-drying. Microscopy demonstrated that mycelia of MBR-52 expanded on the bead surface forming numerous spores. This strain continued to survive on the beads at least 5 weeks when the beads were stocked at −20 to 25°C if the prior incubation at 25°C allowed the strain to colonize well and sporulate before the stock. When tissue-cultured seedlings of mountain laurel were transplanted into soil where the beads with colonizing MBR-52 were buried, rooting from the seedlings was apparently accelerated. MBR-52 was able to be re-isolated from these seedlings, confirming its endophytic colonization. X-ray microanalysis revealed that minerals required for growth of MBR-52 were detected in the bead. Thus, MBR-52 could survive using medium remnants covering the beads and essential inorganic minerals supplied from the beads.