Ilex, a member of the Aquifoliaceae (holly family), comprises more than 500 deciduous and evergreen shrubs or trees with economic importance as crops and ornamentals in tropical and temperate regions of the world (Galle, 1997; Hu, 1989). Ilex glabra (L.) A. Gray (inkberry) is a native evergreen shrub with glossy green foliage and black berry-like drupes. This species grows to a mature height of 1.8 to 2.4 m and a width of 2.4 to 3.0 m (Dirr, 1998). It is a desirable ornamental plant for colder regions. Conventional seed germination and vegetative propagation are two major procedures for mass propagation. However, similar to other Ilex species, seed germination of inkberry is inefficient as a result of low germination rate, long germination time, and seedling variation. It may take 2 to 3 years to overcome the double dormancy caused by hard, impermeable seedcoat and immature embryos (Dirr and Heuser, 1987). In addition, vegetative propagation of inkberry by cuttings may be subject to seasonal variations.
Tissue culture is a well-known and efficient tool for mass propagation of uniform plants. In vitro culture of zygotic embryos for propagation of various Ilex species plants from rudimentary embryos has been reported (Hu, 1975, 1976; Hu et al., 1979; Mattis et al., 1995; Sansberro et al., 1998, 2001a). They focused on the influences of different factors on overcoming dormancy in rudimentary embryos. Hu (1989) reported that cell suspension cultures and somatic embryos were obtained from immature Ilex aquifolium L. (English holly) zygotic embryos; however, the conversion rate of embryos into plants was low. In general, Ilex species have been propagated by shoot proliferation using nodal segments, shoot tips, and/or apical meristems (Bernasconi et al., 1998; Luna et al., 2003; Majada et al., 2000; Mattis et al., 1995; Morte et al., 1991; Sansberro et al., 1999, 2000, 2001b; Zaniolo and Zanette, 2001).
Because there is no reported protocol for mass propagation of inkberry using tissue culture, our evaluation of this procedure includes the study of the effects of plant growth regulators on shoot proliferation and rooting.
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