Evaluation of the Role of Light Intensity and Hormonal Treatments during In Vitro Rooting of Myrtles Micropropagated Plantlets Related to Acclimatization Performances

Myrtus communis L. is a Mediterranean species well known for ornamental and industrial utilization; the micropropagation protocol has been established and used by commerciai firms but the acclimatization phase must be investigated in greater depth. Furthermore owing to its peculiar characters, this species could be a model plant for woody shrub cultured in vitro. It is well known that the quality of plantlets cultured in vitro is the bottleneck affecting the acclimatization phase of micropropagated plants of many species; thus, the aim of this study was to examine the effect of several variables (Iight intensity, hormonal treatments) on chlorophyll content, on plant quality and acclimatization performance. Three Myrtle ornamental genotypes differing in height and other morphological characters, were cultured in vitro at 3 PPFD (25-50-100 micromol m-2 S-I) combined with hormonal rooting treatments including auxins (lAA and IBA) and the cytokinin BA. After 40 days, rooted and non rooted plants were transferred in the greenhouse for acclimatization. High light intensity decreased the chlorophyll (a+b) level in both rooted and non-rooted plantlets. The addition of a small amount of BA (0.1 mg L-I) in the rooting medium produce a higher rooting percentage and higher chlorophyll content compared to the other culture conditions. It is also interesting to note that in this species non-rooted plants cultured in vitro in the presence of BA and having a higher chlorophyll content survived better to the transfer in acclimatization.