Explants of the triploid of Chinese white poplar were transformed with Agrobacterium tumefaciens LBA4404 carrying the expression vector pBtiA containing two insect-resistant genes (Bt Cry1Ac gene and API gene). The expression of exogenous gene of transgenic subclones was analyzed by ELISA detection, Western blotting and laboratory bioassay with Clostera anachoreta Fabricius and Lymantria dispar L. The relationship among the characters of expression of exogenous gene was analyzed. The results showed that on average 41% of 28 transgenic subclones had a high insect resistance (larval mortality more than 80%) against C. anachoreta, 35％ of them had middle insect resistance (larval mortality 40%-80%) and 24% of them had a lower insect resistance (larval mortality lower than 40%). Also 70% of the transgenic subclones had a high insect resistance against L. dispar. Transgenic plant could obviously inhibit the growth and development of the larva, and the inhibition effect of the subclones was different. The expression of exogenous genes in transgenic plant was stable. Correlation among larval mortalities of the transgenic subclones was significant in the two years tested. The transgenic plant showed insect resistance against C. anachoreta and L. dispar, and the resulted larval mortalities in the two insects were significantly correlated. ELISA detection indicated that the expression level of Bt toxoprotein in different subclones was varied in 0.0011％-0.0161％. The obvious correlation between insect mortality and Bt toxoprotein content was proved. This suggested that Bt Cry1Ac gene plays an important role in insect resistance. The transgenic plant also showed some resistance against kanamycin. But the correlation between the resistances against insect and that against kanamycin was not significant. This suggested that selection only with kanamycin could not reflect the plant insect resistance exactly.

Key words: Triploid Chinese white poplar; transgenic plant; exogenous gene; insect resistance