The ability for adventitious rooting of micropropagated shoots from juvenile and mature Pinuspinaster~dt. explants was assessed in vitro on a rooting expression medium. The different rooting traits observed, namely the rooting rate, the number and the length of the adventitious roots, and the root score, were greatly influenced by the age of the donor plant: 98% of juvenile explants rooted, while only 49% of mature explants did. Addition of activated charcoal in the rooting expression medium improved the overall rooting capacity of the mature explants to an average of 78%. Whatever the plant material, the number and the length of the adventitious roots, as well as the root score, fluctuated according to the sampling date.

Cryopreservation of a core collection of 444 elm (Ulmus spp.) clones in liquid nitrogen was carried out by two laboratories participating in a European project of conservation of elm genetic resources. Plant material, collected in nine European countries, represented a large sample of the genetic diversity within three European elm species and their hybrids. The cryopreservation technique used in both laboratories involved the stepwise freezing of cryotubes containing dormant buds. Comparisons with fresh buds showed that the cryopreservation treatment had no negative effect on the viability and regrowth potential of frozen buds. Tests on a random sample of 26 clones showed that direct regrowth of cryopreserved buds (i.e., through propagation by microcuttings) of Ulmus minor and Ulmus laevis was possible; conversely, Ulmus glabra could only be regrown through micrografting. Most thawed explants from all 26 clones survived through the whole cultivation phase and were successfully transferred to the field. A calculation of costs indicates that cryopreservation of elm buds is economically competitive to field clonal archives.

Acclimatized Pinuspinaster Ait. plants originating from five different invitro culture origins were compared morphologically. After one growing season in the greenhouse, the plants displayed the following order of maturity (from juvenile to mature): (i) young seedlings; (ii) plants produced by adventitious budding from cotyledons; (iii) plants derived from micrografted meristems of 2-year-old seedlings; (iv) plants derived from micrografted meristems of a 13-year-old mature clone; and (v) plants derived from microcuttings of axillary shoots of the same 13-year-old mature clone. Plants derived from micrografts exhibited substantial variability with regard to morphological characteristics. This variability included some striking demonstrations of morphological rejuvenation among the mature clone micrografts which, on average, showed more juvenile traits than the microcuttings of the same clone.

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