In vitro androgenesis in apple

Abstract

Most temperate fruit trees are characterized by a long reproductive cycle and juvenile phase (both of several years), a tendency to allogamy and a large tree size. Fruit trees are generally highly heterozygous, outbreeding species, which are propagated asexually. For these reasons, their genetic improvement by conventional methods is time-consuming and limited by space required for field experiments. The production of haploids offers new possibilities for genetic studies and for an increased efficiency in selection. Successful in vitro approaches to induce haploids in apple (Malus domestica Borkh.; 2n=2x=34) have been rather limited in comparison with other plant species, until recently (Höfer and Lespinasse, 1996). The methods generally used for haploid induction are: in vitro androgenesis by anther and microspore culture; in vitro gynogenesis by unfertilized ovule culture, and in situ parthenogensis by irradiated pollen followed by in vitro culture of immature embryos or cotyledons. Due to higher efficiency, a description of methods in this manual will be limited to the protocols of anther and microspore culture. Anther culture in apple was pioneered by Japanese scientists at the beginning of the 1970s. They induced calli capable of root formation. Subsequently, several working groups initiated haploid induction in apple by anther culture and the induction of embryogenesis. However, limited plant formation has been reported. For further details of protocols and results see the review by Höfer and Lespinasse (1996).