Tissue Culture Techniques for the Production of Interspecific Hybrids in Poland: History and Achievements

Abstract

Interspecific hybridization is a significant plant evolutionary process and, concomitantly, a frequently used method to broaden the genetic variability of species and genetically improve crops. However, in distant crosses, many prezygotic and postzygotic barriers are encountered that prevent free, uncontrolled gene flow between species. Therefore, various experimental methods exploiting tissue culture, such as in vitro fertilization, embryo rescue, and protoplast fusion, have been developed to raise hybrids that cannot be obtained naturally through conventional approaches. Professor Maciej Zenkteler of the Adam Mickiewicz University in Poznań pioneered the use of tissue culture in Poland to overcome barriers to sexual crossing. In the mid-1960s, he employed in vitro pollination in which pollen grains were directly applied onto the surface of exposed ovules as the primary method to bypass prezygotic barriers and in vitro culture of isolated ovules and developing embryos (embryo rescue) to overcome post-zygotic barriers. These approaches proved effective for species possessing numerous ovules and large placentas, such as representatives of the families Caryophyllaceae, Solanaceae, and Brassicaceae. Soon thereafter, these methods were extended to other Polish institutes and universities and applied for crop improvement, such as for the production of intergeneric hybrids between Salix and Populus species, resynthesis and broadening of the genetic variability of oilseed rape ( Brassica napus L.), and the generation of new interspecific hybrids of Allium . In the late 1970s, Professor Zenkteler was the first to undertake protoplast fusion. At that time, it appeared that no incompatibility could exist at the fusion level and that somatic hybridization would supersede the possibilities offered by sexual hybridization; however, the reality turned out to be slightly harsh. Nonetheless, successful regeneration of different interspecific hybrids of potato, tomato, or gentians has been achieved by Polish research groups thus far.