Clonal Propagation of Wheat
In spite of the many expectations on the application of tissue culture to plant improvement, clonal propagation is so far the only in vitro tissue culture technique widely used outside the research laboratories. Although most tissue culture techniques all
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1 Introduction In spite of the many expectations on the application of tissue culture to plant improvement, clonal propagation is so far the only in vitro tissue culture technique widely used outside the research laboratories. Although most tissue culture techniques allowing plant regeneration have been proposed as suitable for clonal propagation, only axillary shoot proliferation has been shown to be a reliable and quick method for vegetative propagation of most plant species (Murashige 1978; Bajaj 1986a). The main reason for marginal use and interest of in vitro propagation in agronomic crops is that they can be efficiently propagated by seeds. Nevertheless, vegetative propagation could be very useful also in these species for several specific applications, for instance as a source of experimental material for various types of research. So far, all methods proposed for clonal propagation of cereals and grasses have involved plant regeneration from dedifferentiated tissues or cell suspensions. Plant regeneration, however, shows a number of problems because it is an aleatory, transient, and sporadic event (King et al. 1978; Vasil and Vasil 1980), and only few genotypes respond favorably to callus induction and plant regeneration (Vasil 1982). Furthermore, genetic and cytogenetic instability in callus and cell structures represents a major drawback to the use of these techniques for clonal propagation (D'Amato 1977).
2 Plant Regeneration from Callus Plant regeneration from wheat callus and related subjects have been widely reviewed in a former volume of this series (Crops 1) in common wheat (Bajaj and Gosal 1986) and in durum wheat (Bennici 1986). Therefore, only the aspects concerning clonal propagation will be considered.
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Institute of Agricultural Biology, University of Tuscia, 01100 Viterbo, Italy Institute of Agroforestry, CNR, Porano, Italy
Biotechnology in Agriculture and Forestry, Vol. 13 Wheat (ed. by Y.P.S. Bajaj) © Springer-Verlag Berlin Heidelberg 1990
Clonal Propagation of Wheat
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2.1 Triticum aestivum L.
Since the early reports on plant regeneration from wheat callus (Adachi and Katayama 1969; Shimada et al. 1969), the techniques have been continuously improved, and several papers published in recent years report high efficiency of plant regeneration. However, the genotype influence on callus formation and, even more, on plant regeneration represents a strong limitation to the practical application of these techniques (Vasil 1982). For years, research on wheat tissue culture has been carried out on one or very few genotypes and it has therefore been difficult to evaluate differences in response to tissue culture. The first extensive study on genetic control of callus induction and plant regeneration was carried out by Sears and Deckard (1982). Immature embryos explanted from 39 common wheat genotypes showed very high variability in percentage of callus formation, which ranged from 0 to 97%. Shoot regeneration was observed in 18 genotypes, and only in four of them was the number of plants
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