Field performance of chitinase transgenic silver birch (Betula pendula Roth): growth and adaptive traits

Fifteen transgenic birch lines carrying a chitinase IV gene from sugar beet and non-transgenic control plants were grown in a field trial, and traits connected to growth, quality and adaptation were monitored. Significant variation among the transgenic lines was observed in the growth parameters as well as parameters linked to stress status and leaf phenology of the trees. It was hypothesized that the differences among the lines could be explained by the differences in the level of transgene expression measured as sugar beet chitinase IV transcript accumulation. The level of the transgene expression was not detected to have influence on growth or leaf phenology, but instead it had influence on the parameters related to stress status of a tree. The increased levels of red colour and decreased general condition of the transgenic plants compared to the control plants may indicate physiological stress among the transgenic plants. The proportion of trees infested by Phytobia, larvae of which cause an easthetic defect to birch wood, was lower among many transgenic lines than in controls but the variation in Phytobia occurrence was explained by the differences in plant size only. Three lines out of fifteen were frequently different from the control plants in growth and leaf phenology, and these differences are suggested to be due to the position effect of the transgene. The observed changes in individual transgenic lines were not correlated with the sugar beet chitinase IV expression, and were more likely to impair than improve the traits that are usually considered important in adaptation and birch breeding.