Transgene stability and agronomical performance of two transgenic Basta-tolerant lines of Populus alba L

An experimental trial was established in greenhouse with transgenic white poplars from an elite genotype (Populus alba cv Villafranca) expressing the bar gene for tolerance to BastaR herbicide. The steady-state level of bar mRNA was evaluated in different seasons, over a two year period. Notwithstanding the presence of the 35SCaMV promoter, significant fluctuations in the amounts of bar transcript in relation to season and organ position were observed. The highest expression levels were reached in apical leaves in summer, while a consistent drop in transgene expression occurred at the onset of dormancy and in winter buds. A similar expression pattern was evidenced for the poUBI gene used as endogenous marker. The genetically modified poplars were tolerant to intense and repeated glufosinate ammonium treatments, maintaining an intect shoot sprouting and a good height treatment.