Abstract:

One hundred and sixty five soil samples were collected from Guilin Karst landform area,and 10 strains of Bacillus thuringiensis were isolated from the samples.Light microscope observation indicated that these Bt strains contained crystals in shape of bipyramidal,spherical,square,irregular and so on. Plasmid DNA pattern of the strains formed by agarose gels electrophoresis was compared and it showed a great diversity for these strains.Cryl,cryll,cry2 and cry8 type genes were found in these strains by PCR-RFLP method,but the cry gene-types of two strains G4 and G6 were not known.SDS-PAGE results showed that 10 wild strains could express Cry proteins with 130 kD molecular mass,and 3 isolates could express both 130 kD and 60 kD protein.Bioassay results of the 10 strains indicated that six of them were toxic to Plutella xylostella larvae,and G8 was of highly insecticidal activity to Colaphellus bowringi larvae with 50%lethal concentration(LC50)at 48.2μgml.