In vitro pollination in poplar of section Populus

Two methods of in vitro pollination of aspen were tested and compared, first with moist pollen by transferring swollen pollen grains from a wet agar surface to the stigma and, second, using dry pollen grains. In vitro pollination with dry pollen grains appeared to be more efficient and this method was applied in three subsequent years. Additionally, pollination was performed with selected pollen grains in order to obtain triploid plants. Diploid pollen was induced by heat-treatment of pollen mother cells, but the enrichment of unreduced pollen from natural pollen mixtures was also successful. The selection of diploid pollen, which is larger in diameter than haploid pollen, was performed by sieving using micro sieves. Five triploid plants from different poplar combinations were obtained from 1,227 zygotic embryos cultured after in vitro polli- nation of 2,676 ovaries with dry pollen over 3 years. Embryo rescue was used to facilitate the development of immature zygotic embryos. The results of this study demonstrate the possibility to effect pollination using selected single pollen grains with the help of in vitro techniques