Anther and microspore culture in Camellia japonica

Abstract

Haploid plants have the gametophytic chromosome number. They are of great importance for the production of homozygous plants and for mutation studies. The use of anther and microspore cultures for the induction of pollen embryogenesis hastens the production of haploids and gametoclonal variants. These systems can be useful tools for cultivar improvement. Camellia japonica L. (Theaceae family) is one of the most important species in the genus Camellia. Economically, it is valuable as an ornamental woody species and has a potential to be used for oil and wood production. The available Camellia varieties are genetically highly heterozygous. In this genus, frost and pathogens cause serious damage that results in drastic annual economic loses. So far, in vitro culture of this species, and other Camellia species, has been mainly concerned with the establishment of protocols for micropropagation from juvenile and adult materials (Bennet, 1977, 1978; Bennet & Scheibert, 1982; Carlisi & Torres, 1986; Crezé, 1983; Kato, 1989a; Pedroso-Ubach, 1991; Samartin et al., 1984, 1986; Samartin, 1989; Vieitez et al., 1989a,b, 1992), and for mass propagation by somatic embryogenesis (Barciela & Vieitez, 1993; Kato, 1986, 1989b; Nakamura, 1988; Pedroso & Pais, 1993, 1994d,e; San-José & Vieitez, 1993; Vieitez & Barciela, 1990; Vieitez et al., 1991). Plant improvement has been obtained in some species by field selection and artificial crossing techniques (Yamaguchi et al., 1987). Anther culture, as a strategy for plant improvement, was reported for C. sinensis (Raina & Iyer, 1974; Chen & Liao, 1982, 1988) and C. japonica (Pedroso-Ubach, 1991). In C. sinensis, the production of haploid callus from anthers has been obtained in at least nine cultivars (Raina & Iyer, 1974; Chen & Liao, 1982, 1988) but haploid shoot regeneration was successful only in one of the cultivars (Chen & Liao, 1982, 1988). Embryo production has also been reported in this species by Shimokado et al.(1986) but apparently no plant regeneration was achieved. As far as we know, successful regeneration from anthers and microspore culture has been only reported in C. japonica (Pedroso-Ubach, 1991). Although pollen-derived plants have been obtained by anther culture in many species, plant regeneration from isolated microspores has only been successful in a few species (Bajaj, 1990). Microspore culture presents some potential advantages over anther culture, especially concerning in vitro selection strategies, genetic studies and genetic transformation. The culture of isolated microspores has become a valuable system for studying in vitro embryogenesis (Taylor et al., 1990). Complementing earlier work (Pedroso & Pais, 1992, 1993, 1994c,d), direct microspore embryogenesis in C. japonica would be valuable for studying gene expression during microspore embryogenesis and the factors that divert microspore development onto an embryogenic pathway.