Variations in genome size and chromosome complement of species provide very useful information for biosystematic studies, and also because they influence a range of ecological characteristics. They are also of utmost importance for breeding, especially when in vitro biotechnology tools are used and the need arises to assess the trueness-to-type of regenerated plants. Thus, protocols have existed for a long time for chromosome counting, and more recently also for the determination of the relative nuclear DNA content and genome size. It has also been shown that these latter traits are strongly correlated to regeneration competence and, more generally, to developmental processes in plants. This article will briefly review such approaches from a methodological and breeding-oriented viewpoint.

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In vitro morphogenesis from cotyledon and epicotyl explants and flow cytometry distinction between landraces of Bambara groundnut [Vigna subterranea (L.) Verdc], an under-utilised grain legumeAbstract The morphogenetic competence of Bambara groundnut was assessed for different landraces, explant sources and media compositions. With cotyledon explants, the best callusing occurred on a medium containing 3 mg/l BAP + 0.5 mg/l NAA, while roots were produced with 3-5 mg/l BAP + 0.5 mg/l NAA. Shoots regenerated (~6%) from cotyledons on media with BAP alone (3-5 mg/l) or combined with 0.01-0.1 mg/l NAA. Flowers were regenerated on 5 mg/l BAP + 0.5 mg/l NAA, without any intervening callus phase. With epicotyls, the highest callusing was on 3 mg/l BAP + 0.5 mg/l NAA, and shoots regenerated (15-20%) on 3 mg/l BAP alone or with NAA at concentrations that depended on the landrace studied. Regenerated shoots rooted on hormone-free medium, and plants transferred to the greenhouse were all morphologically normal and fertile. Flow cytometry showed that most regenerants were diploid and in addition permitted to distinguish between landraces according to their relative nuclear DNA content. This is the first report on de novo regeneration in vitro of Bambara groundnut, an important yet neglected legume crop.

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Mesophyll protoplasts of wild pear (Pyrus communis var. pyraster L., Pomoideae) were chemically fused with cell suspension protoplasts of cherry rootstock Colt (Prunus avium x pseudocerasus, Prunoideae), following an electroporation treatment of the separate parental protoplast systems. Fusion-treated protoplasts were cultured, on modified K8P medium, where it had been previously established that neither parental protoplasts were capable of division. Somatic hybrid calli were recovered and, following caulogenesis on MS medium with zeatin and after rooting of regenerated shoots, complete trees were obtained and grown in vivo. Hybridity of these trees was confirmed based on morphological characters, chromosome complement and isozyme analysis. Two separate cloned lines of this intersubfamilial rootstock somatic hybrid (wild pear (+) Colt cherry) were produced. This is the first report of the production of somatic hybrid plants of two woody species, of agronomic value, within the order Rosales.