Ecophysiological competence of Populus alba L., Fraxinus angustifolia Vahl., and Crataegus monogyna Jacq. used in plantations for the recovery of riparian vegetation.

In many semi-arid environments of Mediterranean ecosystems, white poplar (Populus alba L.) is the dominant riparian tree and has been used to recover degraded areas, together with other native species, such as ash (Fraxinus angustifolia Vahl.) and hawthorn (Crataegus monogyna Jacq.). We addressed three main objectives: (1) to gain an improved understanding of some specific relationships between environmental parameters and leaf-level physiological factors in these riparian forest species, (2) to compare the leaf-level physiology of these riparian species to each other, and (3) to compare leaf-level responses within native riparian plots to adjacent restoration plots, in order to evaluate the competence of the plants used for the recovery of those degraded areas. We found significant differences in physiological performance between mature and young white poplars in the natural stand and among planted species. The net assimilation and transpiration rates, diameter, and height of white poplar plants were superior to those of ash and hawthorn. Ash and hawthorn showed higher water use efficiency than white poplar. White poplar also showed higher levels of stomatal conductance, behaving as a fast-growing, water-consuming species with a more active gas exchange and ecophysiological competence than the other species used for restoration purposes. In the restoration zones, the planted white poplars had higher rates of net assimilation and water use efficiency than the mature trees in the natural stand. We propose the use of white poplar for the rapid restoration of riparian vegetation in semi-arid Mediterranean environments. Ash and hawthorn can also play a role as accompanying species for the purpose of biodiversity.

Antimitotic agents increase the production of doubled-haploid embryos from cork oak anther culture.

The objective of this study is to induce the nuclear DNA duplication of anther-derived embryos of cork oak (Quercus suber L.) to obtain doubled-haploid plants. Anther culture of this species produces a low percentage (7.78%) of spontaneous diploids, as assessed by flow cytometry. Therefore, three antimitotic agents, colchicine, oryzalin and amiprophos-methyl (APM), were applied in vitro to anther-derived cork oak haploid embryos from six genotypes at different concentrations and for different treatment durations. Antimitotic toxicity was determined by embryo survival. Efficiency in inducing chromosome doubling of haploid embryos was evaluated by flow cytometry measurements and differences were observed between treatments. Nuclear DNA duplication and embryo survival of cork oak haploid embryos was most efficiently induced with oryzalin 0.01 mM for 48 h. Around 50% diploid embryos were obtained. The rate of chromosome duplication induced by APM 0.01 mM was also acceptable but lower than that induced by oryzalin, regardless of the duration of the treatment. Colchicine 1.3 or 8.8 mM was the least efficient, with the induction of necrosis and only a small rate of nuclear DNA duplication.

Microspore-derived embryos from Quercus suber anthers mimic zygotic embryos and maintain haploidy in long-term anther culture.

Microspore-derived embryos produced from cork oak anther cultures after long-term incubations (up to 10-12 months) were analysed in order to determine the genetic variability and ploidy level stability, as well as morphology, developmental pattern and cellular organisation. Most of the embryos from long-term anther cultures were haploid (90.7%), corresponding to their microspore origin. The presence of a low percentage of diploid embryos (7.4%) was observed. Microsatellite analysis of haploid embryos, indicated different microspores origins of the same anther. In the diploid embryos, homozygosity for different alleles was detected from anther wall tissues, excluding the possibility of clonal origin. The maintenance of a high proportion of haploid embryos, in long-term anther cultures, is similar in percentage to that reported in embryos originating after 20 days of plating (Bueno et al. 1997). This suggests that no significant alterations in the ploidy level occurred during long incubations (up to 12 months). These results suggest that ploidy changes are rare in this in vitro system, and do not significantly increase during long-term cultures. Microscopical studies of the microspore embryos in various stages revealed a healthy and well developed anatomy with no aberrant or chimeric structures. The general morphology of embryos appearing at different times after plating, looked similar to that of earlier embryos, as well as the zygotic embryos, indicating that they represent high quality material for cork oak breeding.