Pollen competition in silver birch (Betula pendula Roth) : an evolutionary perspective and implications for commercial seed production

Pollen competition arises from differences among pollen donors in pollen-tube growth rate. According to the pollen competition hypothesis, only the fastest-growing pollen tubes are assumed to achieve fertilization. By this thesis, I wanted to obtain new information about pollen competition and nonrandom fertilization and the relationship between pollen and progeny performance in Betula pendula Roth. I also considered the possible consequences of pollen competition for sexual selection, and for commercial production of genetically-improved B. pendula seed. The results of this thesis revealed that pollen competition is a real phenomenon in B. pendula seed orchards. There were significant differences among pollen donors in pollen-tube growth rate and a positive relationship between pollen-tube growth rate and seed siring success. These findings indicate that selection among pollen donors can occur on the basis of the differences in pollen performance. The role of pollen-tube growth rate as a predictor of progeny performance remained obscure. In natural birch stands, the relationship between pollen-tube growth rate and seed siring success might not be as straightforward as in controlled greenhouse conditions. Microclimatic variability and maternal environmental effects have random effects on pollen-tube growth rates and the outcome of pollen competition. Possibilities for pollen competition to lead to ongoing sexual selection and evolutionary consequences are likely to be diminished in nature. Microsite variability and genotype-environment interactions can partly explain the maintenance of variation in pollen-tube growth rates

Siirtogeenisten puiden vuorovaikutukset kasvinsyöjien kanssa

Tieteen tor

Phylogeny of chitinases and its implications for estimating horizontal gene transfer from chitinase-transgenic silver birch (

Chitinases are hydrolytic enzymes that have been employed in biotechnology in attempts to increase plants' resistance against fungal pathogens. Genetically modified plants have given rise to concerns of the spreading of transgenes into the environment through vertical or horizontal gene transfer (HGT). In this study, chitinase-like sequences from silver birch (Betula pendula) EST-libraries were identified and their phylogenetic relationships to other chitinases were studied. Phylogenetic analyses were used to estimate the frequency of historical gene transfer events of chitinase genes between plants and other organisms, and the usefulness of phylogenetic analyses as a source of information for the risk assessment of transgenic silver birch carrying a sugar beet chitinase IV gene was evaluated. Thirteen partial chitinase-like sequences, with an approximate length of 600 bp, were obtained from the EST-libraries. The sequences belonged to five chitinase classes. Some bacterial chitinases from Streptomyces and Burkholderia, as well as a chitinase from an oomycete, Phytophthora infestans, grouped together with the class IV chitinases of plants, supporting the hypothesis that some class IV chitinases in bacteria have evolved from eukaryotic chitinases via horizontal gene transfer. According to our analyses, HGT of a chitinase IV gene from eukaryotes to bacteria has presumably occurred only once. Based on this, the likelihood for the HGT of chitinase IV gene from transgenic birch to other organisms is extremely low. However, as risk is a function of both the likelihood and consequences of an event, the effects of rare HGT event(s) will finally determine the level of the risk

Transgenic Betula pendula expressing sugar beet chitinase IV forms normal ectomycorrhizae with Paxillus involutus in vitro

v2005o