[Isolation and identification of a Streptomyces strain against ginger bacterial wilt caused by Pseudomonas solanacearum Smith].

Streptomyces SR-11 was isolated from the soil of ginger in Sichuan Province against ginger bacterial wilt caused by Pseudomonas solanacearum Smith. It had distinctively inhibitive effect on gram-positive bacterium, gram-negative bacterium and some kinds of pathogenic fungi. It's morphological, cultural physiological, biochemical characteristics, chemotaxonomy and 16S rDNA sequences analysis were studied. The substrate mycelium have no partition, the aerial mycelium are ramose; The spore-bearing filaments are spiral, the spores are oval and the surface are smooth. Cell wall type I, Sugar type C. When SR-11 is matured, the aerial mycelium are gray and the strain can give out an earthy smell. A phylogenetic tree was constructed by comparing with the published 16S rDNA sequences of the related bacteria species. In the phylogenetic tree the overall similarity value between strain SR-11 and 12 type Streptomyces sp are 96.5-98.3%.

[Identification of a pathogenic strain of locusts and its toxicity and pathology].

A pathogen was isolated from naturally dead grasshoppers. Its pathogenicity was testified by law of KOCH. It was identified as Serratia marcescens by physiological, biochemical test and molecular systematic analysis. Toxicity of HR-3 to grasshoppers was assayed by means of oral infection. The results show that the linear regression relationship between the logarithm(y) of HR-3 concentration and the probability (x) of corrected grasshopper morality is y = 1.067 + 0.809x, and the median lethal concentration is LC50 = 1.164 x 10(8) cfu/mLo The infection mechanism of HR-3 to grasshoppers were also studied. The histopathological studies show that midgut epithelia are damaged at the beginning of infection, and then partial denaturalization and putrescence occurr in this area. After 48h infection, vacuoles appear in most regions of midgut epithelia.