In vitro chromosome doubling can be induced by several antimitotic agents. The most commonly used are colchicine, oryzalin and trifluralin. The process of induced chromosome doubling in vitro consists of a typical succession of sub-processes, including an induction phase and a confirmation protocol to measure the rate of success. The induction step depends on a large number of variables: media, antimitotic agents, explant types, exposure times and concentrations. Flow cytometry is the pre-eminent method for evaluation of the induced polyploidization. However, alternative confirmation methods, such as chromosome counts and morphological observations, are also used. Since polyploidization has many consequences for plant growth and development, chromosome doubling has been intensively studied over the years and has found its way to several applications in plant breeding. This review gives an overview of the common methods of chromosome doubling in vitro, the history of the technique, and progress made over the years. The applications of chromosome doubling in a broader context are also discussed.

The genus Rosa has a complex evolutionary history caused by several factors, often in conjunction: extensive hybridization, recent radiation, incomplete lineage sorting, and multiple events of polyploidy. We examined the applicability of AFLP markers for reconstructing (species) relationships in Rosa, using UPGMA clustering, Wagner parsimony, and Bayesian inference. All trees were well resolved, but many of the deeper branches were weakly supported. The cluster analysis showed that the rose cultivars can be separated into a European and an Oriental cluster, each being related to different wild species. The phylogenetic analyses showed that (1) two of the four subgenera (Hulthemia and Platyrhodon) do not deserve subgeneric status; (2) section Carolinae should be merged with sect. Cinnamomeae; (3) subsection Rubigineae is a monophyletic group within sect. Caninae, making sect. Caninae paraphyletic; and (4) there is little support for the distinction of the five other subsections within sect. Caninae. Comparison of the trees with morphological classifications and with previous molecular studies showed that all methods yielded reliable trees. Bayesian inference proved to be a useful alternative to parsimony analysis of AFLP data. Because of their genome-wide sampling, AFLPs are the markers of choice to reconstruct (species) relationships in evolutionary complex groups.

The genetic variation within and between wild apple samples (Malus sylvestris) and cultivated apple trees was investigated with amplified fragment length polymorphisms (AFLP) and microsatellite markers to develop a conservation genetics programme for the endangered wild apple in Belgium. In total, 76 putative wild apples (originating from Belgium and Germany), six presumed hybrids and 39 cultivars were typed at 12 simple sequence repeats (SSR) and 139 amplified fragment length polymorphism (AFLP) loci. Principal co-ordinate analysis and a model-based clustering method classified the apples into three major gene pools: wild Malus sylvestris genotypes, edible cultivars and ornamental cultivars. All presumed hybrids and two individuals (one Belgian, one German) sampled as M. sylvestris were assigned completely to the edible cultivar gene pool, revealing that cultivated genotypes are present in the wild. However, gene flow between wild and cultivated gene pools is shown to be almost absent, with only three genotypes that showed evidence of admixture between the wild and edible cultivar gene pools. Wild apples sampled in Belgium and Germany constitute gene pools that are clearly differentiated from cultivars and although some geographical pattern of genetic differentiation among wild apple populations exists, most variation is concentrated within samples. Concordant conclusions were obtained from AFLP and SSR markers, which showed highly significant correlations in both among-genotypes and among-samples genetic distances.

through enumerating recent introgression of diverse traits in a number of commercial crops.

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In this study, we analysed morphological, anatomical and physiological effects of polyploidisation in Spathiphyllum wallisii in order to evaluate possible interesting advantages of polyploids for ornamental breeding. Stomatal density was negatively correlated with increased ploidy level. Stomatal size increased in polyploids. Tetraploid Spathiphyllum plants had more ovate and thicker leaves. The inflorescence of tetraploids had a more ovate and thicker spathum, a more cylindrical spadix and a thicker but shorter flower stalk. Biomass production of the tetraploids was reduced, as expressed by lower total dry weights, and tetraploids produced fewer shoots and leaves compared with their diploid progenitors. Furthermore, tetraploid Spathiphyllum plants were more resistant to drought stress compared with diploid plants. After 15 days of drought stress, diploids showed symptoms of wilting, while the tetraploids showed almost no symptoms. Further, measurements of stomatal resistance, leaf water potential, relative water content and proline content indicated that the tetraploid genotypes were more resistant to drought stress compared with the diploids.

Polyploidy is widespread in plants and has played a major role in the evolution and diversification of the plant kingdom. Unreduced (2n) gametes are an interesting tool for polyploidisation and the creation of genetic variation in plant breeding. Especially in ornamentals, polyploidisation can broaden attractive features within a species. A Begonia collection was screened on the occurrence of 2n pollen with the aid of four different techniques: pollen size measurement, flow cytometric analysis of nuclei isolated from germinated and non germinated pollen, investigation of the microsporogenesis and analysis of progeny. In ten of the 70 screened genotypes (B. dregei, B. pearcei, B. 'Anna Christina', B. 'Bubbles', B. 'Florence Rita', B. 'Orococo', B. 'Rubaiyat', B. 'Spatflacier', B. 'Tamo' and B276), large pollen were observed with a rather spherical than normal ellipsoidal shape. Flow cytometric data proved that these aberrantly shaped pollen were associated with 2n ploidy levels, although they were not always viable. Meiotic aberrations in these large pollen producers resulted mainly in dyads although also monads, triads and polyads were observed. Successful crosses were obtained with B. dregei, B. 'Orococo', and B276 as pollinators; DNA content had increased in all or a part of the progeny. The results show that the occurrence of 2n pollen is not a rare phenomenon in Begonia

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