Begonias are one of the most popular ornamental plants in the world and are used as garden plants and potted plants, in hanging baskets, and as greenhouse flowers. Many also have large, showy, and long-lasting flowers that vary in color from white and pink to red and yellow. The wholesale value of floriculture crops in the United States was $3.83 billion in 2009, among which bedding and garden plants accounts to $1.81 billion (data from USDA floriculture crops 2010 summary). California and Florida account for 46% of the total bedding and garden plants.
The genus Begonia contains ≈2000 species and belongs to the family Begoniaceae. This genus is classified into three general groups by rootstock and includes the tuberous type, the rhizomatous type, and the fibrous-rooted type (Kishimoto et al., 2002). A widely cultivated species of the tuberous type, B. tuberhybrida, is probably the result of hybridization among several Andean species.
Begonia ×tuberhybrida, generally known as tuberous Begonia, involves numerous strains and cultivars with various plant forms of flower size and color and is one of the most popular flowerpot crops. In addition to ornamental use, the leaves and roots of tuberous Begonias are also used for medicinal purposes (Doskotch and Hufford, 1970; Laferriere, 1992). Begonias are usually propagated by conventional vegetative methods such as stem and leaf cuttings. One of the drawbacks to vegetative propagation by cuttings is this has a low multiplication rate (Peck and Cumming, 1984). In addition, many pathogens such as viruses, bacteria, and fungi can enter plants through cuttings resulting in infection of the plants. To circumvent these problems, in vitro techniques have been explored, albeit in a limited and spotty fashion.
Despite significant advances made in tissue culture in other ornamentals (Debergh et al., 1990; Hedtrich et al., 1983; Teixeira da Silva, 2003; Varshney and Dhawan, 1998), information on Begonia tissue culture and regeneration is limited (Castillo and Smith, 1997; Cherng-Kang and Chih-Cheng, 2009; Espino et al., 2004; Mendi et al., 2009; Takayama, 1990). This is particularly true for Begonia tuberhybrida. In fact, only limited data are available on low-frequency shoot regeneration and rooting from leaves and petioles (Debergh and Maene, 1981; Iida et al., 1986; Kiyokawa et al., 2001; Shimada et al., 2007; Viseur and Lievens, 1987). Also, micropropagation of Begonia using microshoots has limited scale-up potential. It has been observed that not more than 10 cuttings can be harvested from a single proliferating shoot primordium from a large tuber (Peck and Cumming, 1984). Simmonds and Werry (1987) used liquid shaker culture of Begonia ×hiemalis tissues to separate adventitious buds on petiole explants with limited success. Similarly, Nakano et al. (1999) obtained eight to nine adventitious shoots per explant from both leaf and petiole segments of the “rose-formed” strain of hybrid Begonia tuberhybrida Voss. Thus, the establishment of a robust and efficient plant regeneration protocol for Begonia is important, particularly for the development of transgenic ornamentals, an area where little work has been done.
Hence, we report here a novel and high-frequency protocol for in vitro plant regeneration from leaf and petiole segments of Begonia tuberhybrida through direct shoot bud formation, without intervening callus phase, that resulted in complete regeneration of plantlets within 3 months.
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