Denberu Kebede, Solomon Yilma
Abstract: Agricultural pests had and still have a significant role in the recurrence of famine in developing countries. Biological means of controlling pests proved to be a reasonable and safe alternative and/or supportive to chemicals. Bacillus thuringiensis (Bt) is found to produce pro-toxins which have shown insecticidal capacity to larvae of different orders including Lepidoptera. Searching in different environments for new Bt strains with insecticidal potentiality increases the current existing strains. Hence, the study was aimed on isolation and identification of Bt isolates from soil samples collected in different agro-ecologies. Sodium acetate heat treatment technique were used for selective isolation of Bt. Cultural, microscopic and selected biochemical tests were used for further characterization of the obtained isolates. Sixty-nine pure isolates were obtained from seventy-four analyzed soil samples from which 29 isolates based on morphological similarities were selected for characterization. Most of the isolates had morphological (colony color, shape, elevation and margin) similarities. Elliptical or spherical endospore shape were observed among the different isolates and most of them (75 %) possessed elliptical endospore and the rest 25 % have spherical endospore shape. There was a difference among isolates in hydrolyzing esculin indicated that there are strain variations. From the characterized isolates almost all except 09Bt-2 were suspected to be different strains of B. thuringensis and B. sphaericus. The obtained isolates should be screened for larvicidal activity of different insect pest and exploited for their cry gene content using polymerase chain reaction (PCR) since their toxicity is directly related with the content of cry genes.
Keywords: Bacillus thuringiensis, endospore, Ethiopia