Optimisation of regeneration and maintenance of morphogenic callus in pear (Pyrus communis L.) by simple and double regeneration techniques

The purpose of our work was to improve the regeneration capacity of leaf explants and the maintenance of shoot morphogenesis in callus of six pear cultivars: Abate Fetel, Conference, Dar Gazi, Harrow Sweet, Kaiser and Williams, by altering the composition of both regeneration and proliferation media of explant donor shoots, and choosing the right type of explant. Regeneration capacity of leaf explants collected from in vitro shoots has been improved in the majority of cultivars also due to shoot preconditioning. For the first time, long term morphogenic callus production and maintenance have been established in some cultivars by a “double regeneration”. Using this technique, morphogenic callus of two cultivars, ‘Dar Gazi’ and ‘Conference’, was maintained for several subcultures but only when they were initiated from small leaflets – less than 2–3 mm long – which had been collected from the neoformed adventitious buds. MS medium [Murashige, T., Skoog, F., 1962. A revised medium for rapid growth and bioassay with tobacco tissue culture. Physiol. Plant. 15, 473–497] proved to be an efficient regeneration medium by stimulating adventitious buds, while the explants of all cultivars, except for Kaiser, showed a high regeneration capacity when they were collected from shoots proliferated on modified QL medium [Quoirin, M, Lepoivre, P., Boxus, P., 1977. Un premier bilan de dix annees de recherche sur les cultures de meristemes et la multiplication in vitro de fruitiers ligneux. Compte rendu des recherches, Station des Cultures Fruitieres et Maraicheres de Gembloux (1976–1977), 93–117]. This medium conferred leaf expansion, overcoming 90% of regeneration in explants of cv Dar Gazi and Williams. Well expanded leaves were obtained and collected by rooting the shoots, while regeneration percentage was not improved and the number of adventitious shoots was increased in most cultivars, reaching up to 10 shoots per explant. When cefotaxime at 200 mg/l, which is normally effective in controlling Agrobacterium, was used for genetic transformation, regeneration percentage and number of shoots per explant (in leaf explants collected from rooted shoots) were increased and a uniform bud regeneration on all the leaf surface was promoted.L'articolo è disponibile sul sito dell'editore http://www.sciencedirect.co

Olea

The genus Olea contains about 30 species were grouped into three subgenera, Tetrapilus, Paniculatae, and Olea (cultivated olive and wild relatives), found in Asia, Australia and Asia, Africa and Europe, respectively. The species O. europaea L. includes six subspecies: Olea europaea L. ssp. europaea (the Mediterranean olives); O. e. laperrinei (distributed in Saharan massifs of Hoggar, Aïr, Jebel Marra in Algeria); O. e. cuspidata (which moved from South Africa to Egypt, East Australian areas and Hawaii, and from Arabia to northern India and Southwest China); O. e. guanchica (Canary Islands); O. e. maroccana (southwestern Morocco); and O. e. cerasiformis (Madeira). Using molecular markers, it has been ascertained that the Mediterranean olives include the cultivated types (O. europaea L. ssp. europaea var. sativa), the true wild oleaster (O. e. e. var. sylvestris), and the feral form olevaster from seedlings raised from seeds of the cultivated types. The oleaster has a narrow range of distribution and it is often mistaken for olevaster. Recolonization of the Mediterranean basin by Oleaster occurred after the last glacial event, from refuges located in both eastern and western Mediterranean basin areas toward southern Europe. Oleaster is a source of rootstock for propagating new improved cultivated varieties. Cultivated and wild forms have the same diploid chromosome number (2n = 46) and are fully interfertile. Triploid and tetraploid genotypes have been isolated from cultivated O.e.e., but polyploid forms have been found in endangered natural populations of O. e. guancica (tetraploid) and O. e. maroccana (hexaploid). Individual oleaster trees showing superior performance for size and/or oil content of fruit were selected empirically during olive domestication and propagated vegetatively as clones using cuttings that were planted directly or, more recently, grafted onto indigenous oleasters. Genetic markers linked for most important agronomic traits, such as size of the tree, content of secondary products of fruit, flowering induction, oil quality, and biotic and abiotic resistance, will help introgression by conventional breeding of oleaster trait-enhancing genes into cultivated olive. Successful results were difficult to achieve due to both the complex genetic basis of the traits to be improved and the long juvenile period of the progenies that delays the expression of the target traits. In vitro techniques to regenerate doubled haploids from hybrids or somaclonal variation induction may complement classical breeding procedures. Genetic transformation could speed up the development of new genotypes, and transgenic olive plants with modified growth habit and putative induced disease resistance are being tested under filed conditions. However, the development of an efficient regeneration method from mature tissue is the limiting factor for the routine application of this technology to olive genetic improvement.La pubblicazione originale è disponibile sul sito dell'editore http://www.springerlink.co

In Vitro Propagation of Traditional Italian Hazelnut Cultivars as a Tool for the Valorization and Conservation of Local Genetic Resources

The hazelnut (Corylus avellana) is one of the most important crops in the Mediterranean basin. The availability of efficient and reliable in vitro propagation could valorize the local genetic resources. Different studies have been carried out for the definition of an efficient hazelnut micropropagation protocol. These have usually been performed on the most important cultivars, but the application of the micropropagation protocol to the minor ones has produced contradictory results and the technique sometimes had less success than the traditional one. The aim of this work was to gather knowledge and additional information on the in vitro performance of some minor cultivars in comparison with the most used for micropropagation. A revised procedure for the specific medium formulation is suggested. The sterilization and culture establishment phases are discussed in detail. The role of zeatin and 6-benzylamminopurine (BA) in shoot proliferation in the Italian traditional cultivars is compared to improve this phase. The rooting stage proves to be one of the most crucial steps in achieving a large-scale commercial application of hazelnut micropropagation

Plant Cellular and Molecular Biotechnology: Following Mariotti's Steps

This review is dedicated to the memory of Prof. Domenico Mariotti, who significantly contributed to establishing the Italian research community in Agricultural Genetics and carried out the first experiments of Agrobacterium-mediated plant genetic transformation and regeneration in Italy during the 1980s. Following his scientific interests as guiding principles, this review summarizes the recent advances obtained in plant biotechnology and fundamental research aiming to: (i) Exploit in vitro plant cell and tissue cultures to induce genetic variability and to produce useful metabolites; (ii) gain new insights into the biochemical function of Agrobacterium rhizogenes rol genes and their application to metabolite production, fruit tree transformation, and reverse genetics; (iii) improve genetic transformation in legume species, most of them recalcitrant to regeneration; (iv) untangle the potential of KNOTTED1-like homeobox (KNOX) transcription factors in plant morphogenesis as key regulators of hormonal homeostasis; and (v) elucidate the molecular mechanisms of the transition from juvenility to the adult phase in Prunus tree species