A successful application of the embryo rescue technique as a model for studying crosses between Salix viminalis and Populus species

Embryos and plants from the crosses Salix viminalis L. as the female parent and Populus alba L., P. violascens Dode or P. tremula L. as the male parent were obtained by in vitro embryo rescue technique. F1 intergeneric progeny were obtained by overcoming post-zygotic barriers caused by the deficiency of endosperm as nutritive tissue during the first stage of embryo development. Ovules containing immature heart-stage embryos as well as early cotyledonary embryos were isolated and rescued in modified 1/2 MS medium supplemented with 3% sucrose to ensure maturity. Seedlings were cultured under in vitro conditions in 1/2 MS medium that contained 0.2mg l^-1 naphtaleneacetic acid and plantlets after rooting were transferred first into pots and subsequently to the experimental field in the Botanical Garden in Pozna, Poland. After 2 years, the putative hybrid nature of the plants was checked by analysing morphological characters and molecular markers. Scanning electron microscopy, flow cytometry and random amplification of polymorphic DNA screening of individuals confirmed the hybrid nature of the S. viminalis × P. alba and S. viminalis × P. violascens progeny and of 25% of the analysed plants from the cross S. viminalis × P. tremula. This study showed the feasibility of overcoming pre- and post-fertilisation barriers to achieve intergeneric hybrids between species from two genera of Salicaceae. The in vitro system to produce hybrids with characters of both parents could be of great importance for increasing biomass production. This study also opens new opportunities to improve other traits in trees, such as resistance to pathogens inherited from one parent.