Comprehensive characterization of plant material obtained by in vitro androgenesis in apple

In apple Malus × domestica Borkh., double haploid and thus homozygous material was obtained by in vitro androgenesis. Grafted trees of nine lines induced by anther culture and one line induced by isolated microspore culture were investigated at the molecular genetics level and further characterized in the orchard. The double haploid lines originated from five different apple cultivars, which were used as donor material for the in vitro androgenesis. This paper describes a comprehensive evaluation of doubled haploids after a long period in the orchard: including ploidy level using flow cytometry, zygosity state using simple sequence repeat (SSR) marker analysis with a total of 28 SSR markers, resistance traits by screening with linked molecular markers, tree and leaf morphology, pollen fertility of the androgenic genotypes and fruit characteristics. Based on the results obtained we conclude that the use of these homozygous lines in apple breeding is currently not a realistic approach. The homozygous lines characterized in this study will be re-grafted and preserved in the fruit genebank of the Julius Kühn-Institut. They could be used for pre-breeding experiments and detailed basic genetic studies such as whole genome sequencing and transcriptome analysis for avoiding problems during genome assembly and for reducing the number of expressed alleles for one and same gene, respectively. They are intended to be used internally, but also externally by material requests of other interested research institutions.