Wide hybridization can potentially lead to the combination of diverse traits, but these hybrids are often sterile as is the case with the inter-subgeneric hybrid Rhododendron `Fragrant Affinity'. Induction of polyploidy can restore chromosome homology and fertility in wide hybrids. In this study we successfully developed an allopolyploid form of R. `Fragrant Affinity' using oryzalin as a mitotic inhibitor and chromosome doubling agent. Approximate genome size (2C), determined using flow cytometry, was 1.6 pg for the diploid and 3.2 pg for the allotetraploid. Pollen viability, determined by staining and germination tests, was 4% and 0%, respectively for the diploid and 68% and 45%, respectively for the allotetraploid. No seeds were produced when the diploid R. `Fragrant Affinity' was crossed with pollen from viable diploid and tetraploid parents. The allotetraploid produced viable seeds and seedlings when crossed with viable pollen from either diploid or tetraploid parents, including self pollination, demonstrating restored fertility. Additional crosses were successfully completed using the allotetraploid as part of an ongoing breeding program to develop new fragrant, cold hardy, evergreen rhododendron.
The sweet potato (Ipomoea batatas) and its relatives (the batatas complex) appear to have evolved in the New World and radiated over several geographic centers in the tropics and subtropics. Traditional studies on taxonomy, cytogenetics, and reproductive biology of the batatas complex have enabled us to investigate certain evolutionary aspects. We conclude that this complex is a monophytetic, “polyploid pillar”, evolved by chromosome doubling (euploidy) and interspecific hybridization. We apply molecular genetic techniques to detect variation [restriction fragment length polymorphism (RFLP) and DNA fingerprinting analyses] to reexamine some of the evolutionary issues that could not be satisfactorily addressed by the conventional approaches, e. g., phylogenetic history of the batatas group, the diploid ancestors of the polyploid members, homology/diversity of genome(s) within the entire group. We find DNA variation in the hypervariable or multiple copy regions of the genome in Ipomoea species. In addition, we are investigating polymorphism in unique/low copy regions using a battery of DNA sequences from homologous as well as heterologous sources. The success of this study will hopefully shed a new light on the subject of evolutionary biology and may also have potential applications in the sweet potato breeding.
The current Cucumis taxonomic classification places C. hystrix Chakr. in subgen. Cucumis based on its morphological similarities to cucumber (C. sativus L., 2n = 14). However, the chromosome number of C. hystrix was identified as 2n = 24, the same number as in subgen. Melo. Cucumis hystrix is therefore considered the first wild Cucumis species of Asiatic origin possessing 12 basic chromosomes. Thus, any research regarding its biosystematics would challenge the basic chromosome number and geographic location theories that govern the current taxonomic system. The production of the amphidiploid species (Cucumis ×hytivus Chen and Kirkbride, 2n = 38) obtained from the cross between C. hystrix and C. sativus and subsequent chromosome doubling would provide an effective means of investigating the relationship between Cucumis species with two different basic chromosome numbers. Thus, RAPD markers were used to study the taxonomic placement of C. hystrix and its interspecific hybrid with cucumber. Of the 220 arbitrary primers screened, 31 were used for analysis where 402 (96.3%) fragments were polymorphic among the germplasm examined. A UPGMA-based cluster analysis partitioned 31 accessions into two main groups [C. sativus (CS) and C. melo (CM)]. Under the similarity coefficient threshold of 0.23, these two groups can be further divided into five clusters with C. hystrix, C. ×hytivus, and C. sativus as separate clusters in the CS group. A modified taxonomic system is proposed based on these results and findings of a previous chloroplast DNA analysis with the genus Cucumis containing subgen. Cucumis with three species and subgen. Melo with six series.
Oryzalin-induced chromosome doubling in Buddleja to facilitate interspecific hybridization HortScience 42 1326 1328 Greihuber, J. Doležel, J. Lysák, M.A. Bennet, M.D. 2005 The origin, evolution and
species. Rooting Chromsome-doubled ‘Schipkaensis’ Cherrylaurel Induction of polyploids is a common breeding technique in cherrylaurel; however, few studies have examined the rooting ability of chromosome-doubled plants. Schulze et al. (p. 69) compared
adaptability to stressful environments is chromosome doubling ( Levin, 1983 ). Gene redundancy leads to genome buffering by increasing allelic diversity ( Udall and Wendel, 2006 ), thus increasing plant tolerance to environmental stress. Polyploid plants can be
lines from open-pollinated populations of onion Theor. Appl. Genet. 90 263 268 Jakše, M. Havey, M.J. Bohanec, B. 2003 Chromosome doubling procedures of onion ( Allium cepa L.) gynogenic embryos Plant
contents apart from typical chromosome-doubled plants as described in results ( Tables 3 and 4 ). These unexpected DNA content mutants are usually known to occur for the following reasons: failure of homologous pairing, nonseparation of chromosomes, a
Chromosome doubling has been used extensively as a tool for creating novelty in ornamental crops ( Ascough et al., 2008 ; Hancock, 1997 ; Väinölä, 2000 ). Horticultural benefits of polyploidization include thicker stems and leaves, larger and
; Skof et al., 2007 ; van den Bulk et al., 1990 ). Spontaneous polyploidization was reported in several Solanum species, and it was found that polyploids obtained through spontaneous chromosome doubling were genetically more stable than those that were