The effect of two stilbene compounds, pinosylvin and resveratrol, on the growth of several fungi was evaluated in plate tests. Wood decay tests were carried out with birch and aspen samples impregnated with the two stilbenes. In plate experiments, resveratrol had an enhancing effect on growth at concentrations where pinosylvin was already enough to prevent the growth of most fungi studied. Pinosylvin impregnated at 0.2% (w/w) concentration significantly reduced the decay caused by all fungi except Phellinus tremulae. In contrast, a resveratrol content of 0.8%, did not protect the wood from decay. A pinosylvin-synthase-encoding gene from Pinus sylvestris was transferred into aspen ( Populus tremula) and two hybrid aspen clones ( Populus tremulax tremuloides) by Agrobacterium tumefaciens-mediated transformation. Transgenic plants accumulated pinosylvin synthase-specific mRNA and showed stilbene synthase enzyme activity in vitro. Transgenic aspen line H4 showed increased resistance to Phellinus tremulae, while two hybrid aspen transformants decayed faster than the control trees. However, we were unable to detect the accumulation of stilbenes in the transgenic plantlets.

The production of volatile organic compounds (VOCs) through the activation of different signaltransduction pathways may be induced in various biotic and abiotic stress situations having importance e.g. in insect and disease resistance. We compared the emission of VOCs emitted from silver birch Betula pendula Roth (clones 4 and 80) twigs damaged either by larvae of Epirrita autumnata, or infected with pathogenic leaf spot causing fungus Marssonina betulae. We also analysed whether local herbivore damage can systemically induce the release of VOCs from the undamaged top of same sapling. The emissions of methylsalicylate (MeSA), (Z)-ocimene, (E)-b-ocimene, (E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) and linalool were induced from the twigs after 72 h feeding damage by E. autumnata larvae. However, 48 h feeding damage did not induce rapid systemic release of VOCs from undamaged top leaves of the same twigs. Pathogen-infected birch twigs had significantly greater emission of (Z)-ocimene and (E)-b-ocimene than intact control twigs. The emission of DMNT was not significantly induced and MeSA was not found at all after pathogen infection, both being significantly different from herbivore damaged twigs. According to our results leaf fungal pathogen induces VOC emission profile differs from that of arthropod herbivore-damaged leaves, suggesting that birch is able to transmit parasite-specific information via VOC emissions to conspecifics and natural enemies of herbivores.

A sugar beet chitinase gene driven by the (4×) CaMV 35S promoter was introduced into silver birch (Betula pendula) through Agrobacterium-mediated transformation. Transgenic shoots were regenerated and grown on WPM medium supplemented with 150 mg/ml kanamycin. From a total of 220 explants, 52 transgenics were obtained and 13 transgenic lines were randomly taken for molecular analysis to confirm the presence of the introduced sugar beet chitinase 4 cDNA by polymerase chain reaction and Southern hybridisation. All 13 transgenic lines were confirmed to contain the gene and further characterised. Northern blot analysis of total RNA indicated that the transgenic lines differed with respect to the steady-state levels of chitinase mRNA. Transgenic lines with high levels of mRNA of chitinase 4 cDNA consistently showed higher levels of resistance to Pyrenopeziza betulicola than transgenics with intermediate or low mRNA levels or a non-transgenic control plant. This report demonstrates that the constitutive expression of this gene in transgenic birch lines increased the resistance of birch against the leaf spot fungus P. betulicola.

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