POPLAR (POPULUS-NIGRA L) PLANTS TRANSFORMED WITH A BACILLUS-THURINGIENSIS TOXIN GENE - INSECTICIDAL ACTIVITY AND GENOMIC ANALYSIS

Insect-resistant poplar (Populus nigra L.) plants have been produced b y infecting leaves with Agrobacterium tumefaciens strains carrying a b inary vector containing different truncated forms of a Bacillus thurin giensis (B.t.) toxin gene under a duplicated CaMV 35S promoter. Putati ve transgenic plants were propagated by cuttings at two experimental f arms (in Beijing and Xinjiang, China). At 2-3 years after transformati on, 17 of them were selected on the bases of insect-tolerance and good silvicultural traits, and evaluated for insect resistance, for the pr esence of the B.t. toxin DNA fragment (Southern blots and PCR) and for the expression of the transgene (western and northern blots). Somaclo nal variation, as suggested by the appearance of permanent changes in the shape of the leaves, was also investigated with molecular tools (R FLP (restriction fragment length polymorphism), RAPD (random amplified polymorphic DNA) and microsatellite DNA). Bioassays with Apochemia ci neraius and Lymantria dispar on the leaves of the selected clones show ed different and in some cases, high levels of insecticidal activity. The molecular analysis demonstrated integration and expression of the foreign gene. Somatic changes were correlated to extensive genomic cha nges and were quantified in dendrograms, in terms of genomic similarit y. The analysis of control plants suggested that genomic changes were correlated to the in vitro culture step necessary for A. tumefaciens-m ediated gene transfer, rather than to the integration of the foreign g enes. Three transgenic clones (12, 153 and 192), selected for insect r esistance, reduced morphological changes and promising silvicultural t raits, are now under large-scale field evaluation in six different pro vinces in China.