4. Discussion
The ultimate success of tissue culture as a commercial technique of plant propagation depends on the ability to transfer plants out of culture, on a large scale, at low cost and with a high survival rate. The results of this study showed that, at the end of the VP1-stage, the successful plants percentage ranged from 66.6 to 78.3% (Table 1). However, all of these plants survived both of the following VP2- and VP3-stage of the acclimatization program. These results indicate that the VP1-stage is, indeed, the critical stage in the acclimatization program of date palm plants. A low survival rate of about 40–50% has been previously reported on ‘Khalas’ and other cultivars (Awad et al., 2006; Zaid and de Wet, 1999). This might be due to loss of viability as a result of poor control of transpiration from the plants. The culture of date palm tissue in vitro with almost 100% relative humidity within the culture vessel can lead to various abnormalities in the plant structure (Zaid and Hughes, 1995a, 1995b). Plants of many species produced in vitro often show morphological, structural, physiological and biochemical differences from those produced conventionally. These include reduced epicuticular wax deposits, altered