Micropropagation of snapdragon

Several works have been carried out on the in vitro culture of snapdragon cultivars. A large part of them deal with callus formation, protoplast isolation and plant regeneration from callus cultures, whereas others report on a direct way of micropropagation based on multiple shoot formation and the rooting of the formed shoots. The different developmental responses are obtained culturing the explants in nutritious media with different combinations and concentrations of auxins and cytokinins.

The presence of cytokinins (kinetin or BAP) in the medium seems to be favourable for multiple shoot formation (Atkinson et al., 1989; González-Benito et al., 1996). According to Newbury et al. (1992) less callus was formed when shoot tips cultured on 1mg/l BAP, were excised from older plants (greenhouse grown plants vs. 48 day old seedlings). In González-Benito et al. (1996), no callus growth was observed on most media tested.

Rooting is achieved when shoots are cultured in the absence of plant growth regulators (Sangwan & Harada, 1975; Pfister & Widholm, 1984; González-Benito et al., 1996). In González-Benito et al. (1996), the use of IBA at concentrations of 2 mg/l and higher was detrimental to root formation.

The last stage of micropropagation, that is the acclimatization to ex vitro conditions and transfer to the greenhouse, which is critical in many species, can be successfully achieved in snapdragon. For instance, in González-Benito et al. (1996), a 90% survival was obtained when rooted vitroplants were transferred to pots with an autoclaved 3 peat : 1 vermiculite v/v mixture. The potted plants were kept in fully enclosed propagators with transparent lids and the windows of the micropropagators were opened for increasing periods of time each day for 15 days, before being transferred to the greenhouse.

A similar general pattern of response has been found when different snapdragon cultivars have been cultured in the same media, although some differences occur (Newbury et al. 1992). Moreover, the same can be said with regard to the micropropagation of wild types of snapdragon (Antirrhinum majus ssp. barrelieri and A. microphyllum) (González-Benito et al., (1996).

A general protocol for the in vitro propagation of snapdragon would consist of the following: Nodal segments or shoot tips from "mother plants” can be used as explants. The explants can then be cultured on MS + 1 mg/l BAP for multiple shoot formation. Root formation of isolated shoots can take place on MS medium without growth regulators. Initially high moisture conditions are needed for the acclimatization of vitroplants before transfer to greenhouse.

The use of microproopagation techniques in snapdragon may be especially best suited for the propagation of triploid cultivars where sexual propagation is not possible.