Abstract: 12# Bt/CXC is an engineered endophytic bacterium by introducing thecrylA? gene from Bacillus thuringiensis subsp, kurstaki into the chromosome of Clavibacter xyli subsp, cynodontis, which colonizes the vascular system of corn. Bioassays withcorn borer (Ostrinia furnacalis) was conducted and the results showed: at each concentration level, strain 12# had a higher insecticidal activity than Bt strain HD-73 and PBStreated control, causing 63 % mortality at the highest concentration tested, while the mortality rate of larvae ingesting wild-type HD-73 was 53% at the same concentration. Theconcentration-mortality curves of the two strains showed a linear correlation. Strain 12#'scoefficent was bigger than that of HD-73. In planta bioassays, the results showed that in-secticidal activity of corn injected with 12# was obviously better than that of corn seed-treated with 12#. At different injection concentrations, larval mortality waved from 70% to96 96, which were significantly different from those of PBS control. At the same time,strain 12# restrained the development of corn borer so that weight of living larvae were reduced by 26.4 % to 44.5 %. Larvae which lived with inoculated corn did not develop to second instar, while those lived with control developed to four instal.

Key words: Bt/CXC, engineered bacteria, endophyte, corn borer