The in vitro clonal propagation in oaks is an important step in the breeding activity using clonal strategies, and in the same time a tool for the application of somaclonal selection procedures in the improvement of adaptability traits. The use of somatic embryogenesis in oak clonal micropropagation is preferable in the applications concerning somaclonal variation and selection, because the plants regenerated from somatic embryos usually have monocellular origin and consist in clones of long-term culture, submitted of in vitro selection procedures. The somatic embryogenesis in oak, as an alternative to propagation by cuttings, provides the possibility of mass production of cotyledonary embryos, which can be either cryopreserved, or maintained by long-term culture as stable embryogenic somaclones. An experimental device was designed, composed of three oak species and 6 provenances (three of Quercus robur, one of Quercus petraea and two of Quercus frainetto), 4 types of explants (developmental stages of the zygotic embryo) and 4 variants of culture medium. The investigation of factors affecting the embryo induction efficiency, as well as other specific reactions of explants in culture (callogenesis, rhyzogenesis and germination) and of the relationship among these factors acting simultaneously. Plant material: As a genetical background, the plant material was represented by three oak species, in each of them one or more provenances being investigated: Quercus robur (three provenances), Q. petraea (one provenance) and Q. frainetto (two provenances). The immature acorns harvested at 4 different dates were dissected and used as sources of explants. The explants were represented by immature zygotic embryos in different developmental stages or fragments of more advanced embryos. The developmental stages of zygotic embryos have been defined and correlated with the morphological characteristics of acorns. Culture medium: Four media were tested for the induction of embryogenesis, representing combinations between two nutrient recipes and two combinations of growth regulators. Structure of the experiment: 3 oak species: Quercus robur, Quercus petraea, Quercus frainetto; 6 provenances: 3 of Quercus robur, one of Q. petraea and two of Q. frainetto; 4 developmental stages of explants (4 explant types): stages 1, 2, 3 and 4. Three replications consisting of five to ten explants have been counted for each parameter. The most important factor affecting the embryo induction efficiency was the developmental stage of the zygotic embryo used as explant. The best results were obtained with the youngest embryos (stage 1), with a linear decrement towards the stage 4. Inside the same developmental stage, important differences concerning the embryo induction efficiency were observed among species and also among the provenances of the same species. It was found that the most important factor affecting the somatic embryo induction efficiency was the developmental stage of the explant. In all oak species, the embryogenic ability decreased constantly from the youngest to the more advanced zygotic embryos used as explants. The same trend was recognized in the case of the provenances inside the species, regardless the culture medium used for the induction. Correlations coefficients for all 48 pairs of values were calculated, for the ten combinations of the characters, in all species and provenances. The significance of the results was done for P5% and P1%. The simple correlations studied showed that most characters are closely correlated. There are differences among provenances concerning the relationship between the pairs of characters. In Q. robur the provenience has an extremely evident effect. In Q. petraea, all of the correlations are highly significant between all the five characters, positives or negatives. Also in Q. frainetto, for the first provenance, the correlation is significant (for example the rhyzogenesis x the embryo induction efficiency) or highly significant for all the others characters.

Quercus; in vitro; embryo induction; correlations coefficients; somatic embryogenesis

Presentation: oral