Introduction, maintenance and utilization of male sterility in leek (Allium ampeloprasum L.) = [Inductie, handhaving en gebruik van mannelijke steriliteit in prei (Allium ampeloprasum L.)]

This thesis describes research work performed in leek in relation to efforts to obtain or exploit a male sterility system for hybrid leek breeding. Male sterile plants can be found in every leek cultivar. The male sterility trait can be explained by a nuclear monogenic inheritance or by a nucleo-cytoplasmic inheritance. The existence of a nucleo-cytoplasmic inheritance remains speculative unless the maintainer genotype will be identified. No source of CMS has been found, sofar, in leek or related forms of A. ampeloprasum L.

Mutation breeding experiments during an extended period of time, using chemicals or somaclonal variation, did not result in the induction of cytoplasmic male sterile mutants in leek.

The small chances for fixation of a mutation in a mitochondrial genome population and problems concerning the identification and recovery of the cytoplasmic mutation at the plant level may have been the major obstacles in obtaining a cytoplasmic male sterile mutant.

An efficient callus regeneration system and the selection of leek plants with improved regeneration ability are described in this thesis. The availability of a regeneration system is an essential step in the application of somatic hybridization, somaclonal variation and transformation techniques in leek.

Vegetative propagation of nuclear male sterile genotypes remains up till now the most realistic option for producing leek hybrids. A new in vitro method for mass clonal propagation of leek, based on flower stalk explants, was developed and is described in this thesis. This method offers a realistic opportunity to leek breeders for producing leek hybrids, until a less expensive genetic system for producing male sterile lines would become available.