Long-term somatic embryogenesis in olive (Olea europaea L.): Influence on regeneration capability and quality of regenerated plants

In vitro regeneration via somatic embryogenesis is at the base of application of biotechnological tools to olive (Olea europaea L.) genetic improvement. The development of elite plant material utilizing these techniques requires a considerable period of time, but little is known about the real influence of the duration of the maintenance phase on somatic embryogenesis of olive. The objective of this investigation was to evaluate the effect of culture age on the efficiency of the different phases of the somatic embryogenesis process and the quality of the regenerated plants. With this purpose, 10 independent embryogenic lines of two different ages (2 and 8 years) were monitorized throughout the somatic embryogenesis process. Behavior of the regenerated plants was compared with that of seedlings over the subsequent micropropagation, rooting and acclimatization steps. The results showed alteration of the proliferation pattern with time in culture. Efficiency of the maturation phase significantly decreased in aged lines and a decline in embryos quality was observed as revealed by the reduced germination capacity. Both effects gave rise to a significant decrease in the regeneration potential as duration of the proliferation phase increased. Plants obtained from aged cultures were smaller than those derived from young cultures although more shoots developed per germinated somatic embryo. During the elongation phase, shoots derived from younger cultures were more vigorous, giving rise to longer axillary shoots. No significant differences were found in the rest of the parameters studied in the elongation, rooting and acclimatization phases. Behavior of somatic plants during these steps was similar to that of seedlings, thus revealing the high quality of plants regenerated following this somatic embryogenesis protocol. Events involved in loss of morphogenic potential in olive appear to be different than those described in conifer species.