Embryogenic cultures of plants are exposed to various stress factors both in vitro and during cryostorage. In order to safely include the plant material obtained by somatic embryogenesis in combination with cryopreservation for breeding programs, it is necessary to monitor its genetic stability. The aim of the present study was the assessment of somaclonal variation in plant material obtained from embryogenic cultures of Picea abies (L.) Karst. and P. omorika (Pancic) Purk. maintained in vitro or stored in liquid nitrogen by the pregrowth-dehydration method. The analysis of genetic confoimity with using microsatellite markers was performed on cotyledonary somatic embryos (CSE), germinating somatic embryos (GSE) and somatic seedlings (SS), obtained from tissues maintained in vitro or from recovered embryogenic tissues (ETc) and CSE obtained after cryopreservation. The analysis revealed changes in the DNA of somatic embryogenesis-derived plant material of both Picea spp. They were found in plant material from 8 out of 10 tested embryogenic lines of P abies and in 10 out of 19 embryogenic lines of P. omorika after in vitro culture. Changes were also detected in plant material obtained after cryopreservation. Somaclonal variation was observed in ETc and CSE of P omorika and at ETv stage of P abies. However, most of the changes were induced at the stage of somatic embryogenesis initiation. These results confirm the need for monitoring the genetic stability of plants obtained by somatic embryogenesis and after cryopreservation for both spruce species.

Bionomy of spruce spider mite (SSM) (Oligonychus ununguis Jacobi) on five species/cultivars of spruce and two species of cypress was studied under laboratory conditions during rwo consecutive growing seasons. The study showed influence of host-plant food on development time, fecundity and longevity of SSM. The comparison of intrinsic rate of natural increase (r,J indicates the highest reproduction potential of SSM on Picea pungens (0.18), P. abies 'Nidiformis' (0.17), and P. glauca 'Conica' (0.14). SSM had much lowest rm on P. omorica (O.OS) and P abies 'Virgata' (O.Ol). The reproductive potential of SSM on rested species of cypresses was similar: 0.12 and 0.10 on Chamaecyparis lawsoniana 'Golden Wonder" and C. pisifera 'Nana Aureovariegata', respectively. The results obtained clearly indicate that the population parameters can be a proper indicator ofrelative susceptibility/resistance of commercially available species/cultivars of spruce and cypress plants to SSM.

In this contribution, an overview over a numerical scheme for the crack modelling of spruce wood under tensile loading is given. A material model for biaxially stressed spruce wood with consideration of the effect of knots on the strength properties has been developed. A necessary feature of this material model is its ability to treat cracks by means of the so-called smeared crack concept. For this reason the consideration of a so-called characteristic length in the corresponding evolution laws of the strength values is required. The successful implementation in the material model is shown by means of various numerical examples.

Finite element simulations of structures and structural details require suitable material models. Today there is still a lack of such constitutive material models in timber engineering. Therefore, a perennial research project at the Institute for Mechanics of Materials and Structures at the Vienna University of Technology was performed. In this paper the testing equipment, the experiments, the developed material model and its implementation in finite element software will be explained. One focus of the mentioned project is the acquisition of the mechanical behaviour of biaxially, oblique to fibre direction loaded spruce wood. This enables a better simulation of multiaxial stress states in real timber structures. The applicability of the implemented constitutive model will be demonstrated by means of a nonlinear finite element analysis of a bone-shaped test specimen.