Anther culture of linseed (Linum usitatissimum L.)

Linum usitatissimum (L.) is grown as linseed (for oil) or flax (for fibre) and is one of the oldest cultivated plants in temperate regions. The oilseed types (linseed or oil flax) compared to the fibre types (flax) have shorter and thicker stems with more branches, whereas flax produces fewer capsules and smaller seeds. It is an autogamous species with about 5–10% cross-fertilization. Therefore, breeders mainly use pedigree selection, bulk breeding or progeny methods to develop new breeding lines and varieties. Traditional breeding methods are time consuming taking 10–15 years to develop improved varieties. Doubled haploid techniques offer an opportunity to accelerate breeding. In linseed, haploidy can be achieved through polyembryonic seedlings or through in vitro methods of anther or isolated microspore culture. Polyembryony was reported to be the first source of haploid plants in linseed. The diploid part of the twin is derived from the fertilized egg cell and the haploid probably from one of the synergids of the same embryo sac. Polyembryony is genetically determined and high-twinning genotypes with up to 8% twin seedlings were identified. Hybridization and subsequent selection resulted in an increased frequency of twinning seedlings up to 30%. In order to increase the efficiency of haploid plants independent from the hybridization with twinning lines, anther and microspore culture systems were developed. The original protocol for linseed anther culture and root regeneration (Nichterlein et al., 1991; Nichterlein and Friedt, 1993) was further optimized through modifications of the induction medium, and anther pre-treatments (Chen et al., 1998).