Naturally-occurring haploids have been known in the plant kingdom for many years; for example Blackslee et al recorded a haploid mutant of Datura as long ago as 1922. While it was appreciated that doubled haploids would provide the most effective route for the production of homozygous lines for plant breeding, this approach could not be applied since haploid lines were not available for the majority of crop plants. In any event, for such a strategy to be successful, homozygous lines would have to be produced during the breeding programme - and no method for this existed.