Principles of Plant Genetics and Breeding. George Acquaah

early generations prior to homozygosity.

       Genetic issues

      Unlike the conventional methods of inbreeding, it is possible to achieve completely homozygous individuals. Using an F₁ hybrid or a segregating population as female parent in the production of maternally derived haploids increases genetic diversity in the doubled haploid line. It is advantageous if the female also has agronomically desirable traits. F₁ hybrids are suitable because their female gametes will be segregating.

7.18 Germplasm preservation

      Germplasm preservation in tissue culture was discussed in Chapter 6. This method of germplasm storage is often used for vegetatively propagated species.

Key references and suggested reading

      1 Asif, M. (2013). Progress and Opportunities of Doubled Haploid Production, Springer briefs in plant science, vol. 6. Heidelberg: Springer.

      2 Chaudhury, A.M., Ming, L., Miller, C. et al. (1997). Fertilization‐independent seed development in Arabidopsis thaliana. Proceedings of the National Academy of Sciences of the United States of America 94: 4223–4228.

      3 Choo, T.M., Reinbergs, E., and Kasha, K.J. (1985). Use of haploids in breeding barley. Plant Breed Reviews 3: 219–252.

      4 Forster, B.P., Heberle‐Bors, E., Kasha, K.J., and Touraev, A. (2007). The resurgence of haploids in higher plants. Trends in Plant Science 12: 368–375.

      5 Hanna, W.W. and Bashaw, E.C. (1987). Apomixis: its identification and use in plant breeding. Crop Science 27: 1136–1139.

      6 Humphreys, D.G. and Knox, R.E. (2015). Doubled Haploid Breeding in Cereals Advances in Plant Breeding Strategies: Breeding, Biotechnology and Molecular Tools, 241–290. New York: Springer.

      7 Jain, M., Chengalrayan, K., Gallo‐Meacher, M., and Misley, P. (2005). Embryogenic callus induction and regeneration in a pentaploid hybrid bermudagrass. cv Tifton 85. Crop Science 45: 1069–1072.

      8 Janhar, Elias, E.M., and Rao, M.B. (2004). Effects of growth regulators on in vitro plant regeneration in durum wheat. Crop Science 44: 1839–1846.

      9  Kamo, K. (1995). A cultivar comparison of plant regeneration from suspension cells, callus, and cormel slices of Gladiolus. In Vitro Cellular and Developmental Biology 31: 113–115.

      10 Kindinger, B., Bai, D., and Sokolov, V. (1996). Assignment of a gene (s) conferring apomixis in Tripsacum to a chromosome arm: cytological and molecular evidence. Genome 39: 1133–1141.

      11 Koltunow, A.M., Bicknell, R.A., and Chaudhury, A.‐M. (1995). Apomixis: molecular strategies for the generation of genetically identical seeds without fertilization. Plant Physiology 108: 1345–1352.

      12 Maluszynski, M., Kasha, K., Forster, B.P., and Szarejko, I. (2003). Doubled Haploid Production in Crop Plants: A Manual. Dordrecht: Springer.

      13 Mohammadi, S.A., Prasanna, B.M., and Singh, N.N. (2003). Sequential path model for determining interrelationship among grain yield and related characters in maize. Crop Science 43: 1690–1697.

      14 Murashige, T. and Skoog, T. (1962). A revised medium for rapid growth and bioassays with tobacco tissue culture. Physiologia Plantarum 15: 473–497.

      15 Snape, J.W. (1989). Doubled haploid breeding: theoretical basis and practical applications. In: Review of Advances in Plant Biotechnology 1985–1988: 2nd International Symposium on Genetic Manipulation in Crop (eds. A. Mujeeb‐Kazi and L.A. Sitch), 19–30. Philippines: CIMMYT Mexico DF and IRRI Manila.

      16 Stefaniak, B. (1994). Somatic embryogenesis and plant regeneration of gladiolus. Plant Cell Reports 13: 386–389.

      17 Tae‐Seok, K.O., Nelson, R.L., and Korban, S.S. (2004). Screening multiple soybean cultivars (MG 00 to MG VIII) for embryogenesis following Agrobacterium‐mediated transformation of immature cotyledons. Crop Science 44: 1825–1831.

      18 Touraev, A., Forster, B.P., and Jain, S.M. (2009). Advances in Haploid Production in Higher Plants. Dordrecht: Springer.

      19 Trigiano, R.N. and Gray, D.J. (eds.) (1996). Plant Tissue Culture Concepts and Laboratory Exercises. New York, NY: CRC Press.

Internet resources

      http://aggie-horticulture.tamu.edu/tisscult/microprop/microprop.html – (links to numerous aspects of plant micropropagation).

      http://billie.btny.purdue.edu/apomixis/apomixis.html – Excellent overview of apomixis.

      http://www.sprrs.usda.gov/apomixis.htm – Comments from foremost scientists in field of apomixis.

      http://www.blogontheweb.com/tissue_culture – Excellent discussion on tissue culture.

Outcomes assessment

      Part A

      Please answer the following questions true or false:

      1 The MS medium was developed by Morris and Stevenson.

      2 Agar is used as a gelling agent in tissue culture.

      3 A protoplast is all the cellular components of a cell plus the cell wall.

      4 An auxin‐cytokinin ratio in favor of auxin promotes rooting.

      5 Propagation by cuttings is a form of clonal propagation.

      6 Diplospory is the most common mechanism of apomixis in higher plants.

      7 Facultative apomicts reproduce exclusively by apomixis.

      8 Pathogenesis is equivalent to haploidy.

      Part B

      Please answer the following questions:

      1 The part of the plant used to start tissue culture is called the ……………………..

      2 The MS tissue culture medium is named after ……………… and ……………

      3 A mass of undifferentiated cells, such as meristematic cells, is called ………….

      4 What is clonal propagation?

      5 What is apomixis?

      6 Distinguish between apospory and displospory as mechanisms of apomixis.

      7 Species that reproduce exclusively (or nearly so) by apomixis are described as …………………………..

      8 Give a specific advantage of clonal propagation.

      Part C

      Please write a brief essay on each of the following topics:

      1 Why is it possible (at least theoretically) to raise a full plant, or for that matter any organism, from just one of its own cells?

      2 All cells are not totipotent. Explain.

      3 What it the importance of a callus phase in plant tissue culture research?

      4 Discuss the rationale for the composition of a tissue culture medium.

      5 Describe the in vitro production of hybrids.

      6 Discuss practical applications of tissue culture in plant breeding.

      7 Discuss the