Production and application of doubled haploids in crops

Haploid plants (containing the gametic chromosome number n of a species) can be produced by a number of methods and have been reported in well over 200 plant species. However, only two methods have been capable of producing large numbers of haploids from most genotypes: chromosome elimination following wide hybridization and in vitro culture of gametes, either microspores (androgenesis) or megaspores (gynogenesis). Chromosome elimination was first established in barley and has been utilized in the production of over 20 cultivars in this crop. Chromosome elimination was also established as a method for producing haploids in wheat, either from crosses with Hordeum bulbosum or maize pollen with the latter being used in commercial breeding programmes. Production of haploids (dihaploids) in cultivated potato (Solanum tuberosum 2n = 4x = 48) by crossing with S. phureja (2n = 2x = 24) appears likely to also occur through chromosome elimination. However, because of the large number of microspores in anthers, androgenesis has the potential to be much more efficient than chromosome elimination in the production of haploids and is available in more crop species. Frequent questions posed by breeders, including the relative costs, are discussed. Application of doubled haploids in breeding programmes is now established for a number of crops and many cultivars have been released from programmes using haploidy procedures. In the area of molecular genetics, haploid procedures have proved to be very beneficial in developing molecular maps and in analysing quantitative trait loci. Isolated microspores have also been the target of research in transformation and in vitro selection in crops, with limited success reported. (author). 43 refs