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Pilar Andreu, Arancha Arbeloa, Pilar Lorente and Juan A. Marín

Salt tolerance varies between species and genotypes of plants, but evaluation of these differences is cumbersome, because whole plants that are highly complex systems show a variety of responses depending on the applied methodology. However, focusing on plant roots, which are in direct contact with the soil, could offer a simpler and more efficient model for analyzing salt stress tolerance in different species. This study explores whether root growth under salt stress is associated with genotypic differences in Prunus species with different degrees of salt tolerance. Excised root cultures were grown in vitro under increasing salt concentrations (0, 20, 60, and 180 mm NaCl). Root tips taken from in vitro-rooted shoots of Prunus species with different salt tolerance were measured after 3 weeks of culture in a shaker, and changes in their anatomy were examined. Both growth and starch content of in vitro root cultures were affected by salt concentration. Root length increments were related to salt stress tolerance at 60 mm NaCl, in which significant differences were also found between species. A significant inverse correlation was found between salt tolerance and starch accumulation in the maturation zone of root tips. Genotypic differences were observed in agreement with species' salt stress tolerance in vivo. These results suggest the use of excised root cultures for rapid, early detection of salt stress tolerance in plants. Chemical names: sodium chloride (NaCl).

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Arancha Arbeloa, Ma Elena Daorden, Elena García, Pilar Andreu and Juan A. Marín

In vitro embryo culturing has arisen as a powerful tool for embryo germination of low-viability seeds. This tool has been used to germinate seeds of early-maturing or hybrid Prunus species. ‘Myrobalan’ (Prunus cerasifera Ehrh.) is a widely used rootstock for plum and apricot cultivars and its interspecific hybrids have a clear potential for breeding purposes. However, early seed abortion is often a problem in interspecific crosses because no protocol has been established yet for ‘Myrobalan’ seeds. In this work, we developed a procedure for in vitro germination of embryos of different sizes. Various factors affecting embryo germination such as the culture media, the presence of cotyledons, the stratification temperature, and the embryo size were tested in three different ‘Myrobalan’ clones. The developed protocol includes the use of full embryos that were stratified at 4 °C and cultured in C2d culture medium. The germination rate was strongly affected by the embryo size and reached 90% germination with intermediate- to large-sized embryos (6.5 to 10 mm). However, smaller embryos could also be germinated, and up to 30% germination was achieved with 0.5- to 2-mm long embryos. The results obtained here provide a protocol for in vitro germination of ‘Myrobalan’ embryos that will likely be helpful in breeding programs.