Abstract: 【Aim】 To study the combining effects of two or more insect-resistance genes in plants, as well as to screen and confirm double Bt transgenic 741 poplar lines with high resistance against coleopteran and lepidopteran insects. 【Methods】 Eight lines with three transgenes (Cry3Aa+Cry1Ac+API), one line with double transgenes (Cry1Ac+API) and three lines with single transgene (Cry3Aa) of transgenic 741 poplar were used as experimental materials. Comparative studies were conducted from three aspects: PCR detection of exogenous gene, the expressions of insecticidal proteins and the assessment of insect-resistance ability of plant. 【Results】 The expected electrophoretic bands from the transgenic lines appeared in PCR amplification. ELISA detection showed that the expression of insecticidal proteins was consistent with the exogenous genes in each line. Toxicity tests were performed in the laboratory with Plagiodera versicolora and Hyphantria cunea on fresh detached leaves. Transgenic poplar lines carrying different insect-resistance genes demonstrated selective resistance to target insects, but showed no toxic effects towards non-target insects. Transgenic 741 poplar lines with double Bt transgenes had double insect-resistance ability, and individual lines showed resistance ranging from high, medium to low. Five lines (pCCA1, pCCA2, pCCA5, pCCA6 and pCCA9) selected with high resistance against P. versicolora showed higher toxicity than three single Cry3Aa gene lines with high resistance (pCC11, pCC53, and pCC84). As regard to resistance toward H. cunea, seven lines (pCCA2-pCCA7 and pCCA9) exhibited similar effectiveness as the single Bt line (pB29) and only one line (pCCA1) showed an extremely low level of resistance. 【Conclusion】 The combination of multiple insectresistance genes in 741 poplars exerts gene stacking effects which not only expand its insect-resistance spectrum but also improve its insect-resistance ability largely.

Key words: 741 poplar, exogenous gene, single Bt gene, double Bt genes, insect-resistance