Intergeneric crossability studies on obtaining hybrids between Salix viminalis and four Populus speciesIn vivo and in vitro pollination of pistils and the formation of embryos and plantlets

For the first time, hybrid embryos and plantlets were obtained from in vitro-pollinated whole catkins of Salix viminalis with pollen grains of Populus tremula, P. tomentosa and P. alba. Only hybrid embryos were obtained from cross S. viminalis with P. lasiocarpa. Pollen of poplar species germinated on stigmas of willow and some pollen tubes were observed growing into the ovary. After 36–48 h of pollination, several-celled globular embryos were found inside the embryo sacs. During the next 14 days in some ovules, the process of embryogenesis proceeded similarly as in the control material, that is after selfing in vitro. In some other embryo sacs embryos degenerated mainly at the globular stage. Endosperm development was poor or not present. Out of 599 catkins, which jointly included around 80.000 pistils, 141 fully developed embryos were isolated and transferred into MS medium with whole or half concentrations of macroelements. From about 65% of the cultured embryos, plantlets were established. Further investigations are in progress on finding the suitable environmental conditions for culturing plantlets in soil and establishing the hybrid characteristics of the progeny.