Author
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Reed, Sandra |
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Submitted to: Plant Tissue Culture and Development
Publication Type: Book / Chapter Publication Acceptance Date: 5/15/2003 Publication Date: 3/2/2004 Citation: Reed, S. Haploid Cultures. Plant Development and Biotechnology, R.N. Trigiano and D.J. Gray (eds), CRC Press. 2004. pp:225-234. Interpretive Summary: Haploid plants, in which chromosome number has been reduced by half, are valuable tools for genetic and plant breeding studies. While haploidy sometimes occurs in nature, it occurs too infrequently to be of practical use. Various in vitro, or tissue culture, techniques have been developed for producing haploids in a number of plant species. This chapter reviews these techniques, with particular emphasis on factors important to the successful induction of haploidy. The most commonly used method of producing haploids is through the in vitro culture of anthers, which are the pollen-bearing parts of plants. The process by which haploid plants develop from cultured anthers is known as androgenesis. Haploids produced via androgenesis develop from immature male germ cells. Haploids have also been produced by placing unfertilized ovules or ovaries into culture. In this process, which is called in vitro gynogenesis, haploids arise from female germ cells within embryo sacs. The success of in vitro androgenesis and gynogenesis is strongly influenced by species, media formulation, and development stage of the pollen or embryo sac at time of culture. Haploids of several important crop species are currently produced routinely, and their use in breeding programs has shortened the time needed for developing new cultivars. Expansion of this valuable breeding technique to additional species should occur as continued efforts are made to identify factors critical to the in vitro induction of haploidy. Technical Abstract: Haploids are valuable tools in genetic studies and breeding programs. Spontaneous haploidy has been reported in many species, but usually occurs at a low frequency. Greater numbers of haploids have been produced using in vitro procedures. Anther culture has been the most widely used in vitro technique for producing haploids, but androgenic haploids have been obtained in a few species through the culture of isolated microspores. While fewer studies have dealt with the induction of haploids from the female gametophyte, in vitro gynogenesis has proven successful in several species. Yields of androgenic and gynogenic haploids differ greatly depending on species, and are also affected by cultural conditions, such as media formulation, stage of microspore or embryo sac at time of culture, and use of a low- or high-temperature pre-treatment. Both androgenic and gynogenic haploids may either arise directly or be produced indirectly through a callus intermediate. In vitro-derived dihaploids, or chromosome-doubled haploids, of several important crop species are currently produced routinely. Use of dihaploids in breeding programs of these species has shortened cultivar development time. Expansion of this valuable breeding technique to additional species should occur as continued efforts are made to identify factors critical to the in vitro induction of haploidy. |
