Gaura lindheimeri is a diploid herbaceous perennial species native to Texas and Louisiana and winter hardy only to USDA hardiness zone 5. A potential source of winter hardiness is G. coccinea Pursh., a polyploid widely distributed in North America; of particular interest are autotetraploid populations of G. coccinea from Minnesota. To facilitate interspecific hybridization, a tetraploid G. lindheimeri would be advantageous. Two G. lindheimeri genotypes, MN selections 443-1 and 01G-02, were treated with two different antimitotic agents at two concentrations, trifluralin—15 and 30 μm and colchicine—0.25 and 1.25 mm, along with appropriate controls, to determine the frequency of chromosome doubling. Two-node stem sections were treated for 12, 24, or 48 h and then rooted and grown to flowering. Pollen diameter was measured as an indicator of chromosome doubling in cell layer LII, and morphologic characteristics (days to flower, flower size, plant height, inflorescence height, and plant width) were recorded for all plants. Chromosome doubling was not observed in any plant treated with trifluralin. Based on pollen diameter, genotype 443–1 only had chromosome doubling in the colchicine 1.25 mm concentration when treated for 12 h. All durations of colchicine at 1.25 mm were successful for genotype 01G-02 as well as a small percent treated with colchicine at 0.25 mm treated for 48 h. Autotetraploid plants (2n = 4x = 28) had larger flowers in both genotypes, and autotetraploid derivatives of genotype 01G-02 flowered earlier and were taller than diploid plants. Conformation changes from three-lobed to four-lobed pollen grains were observed when pollen diameter approached that expected of 2n pollen. Visual screening of pollen for conformation changes can quickly determine if chromosome doubling in cell layer LII has occurred. With the autotetraploid G. lindheimeri derived from colchicine application, crosses can be performed with autotetraploid G. coccinea to introgress cold tolerance. Additional breeding can also be done at the tetraploid level to develop new autotetraploid cultivars of G. lindheimeri.
Chromosome doubling has been widely explored as a bridge to help gene introgression between different ploidy levels both between and within species for crop improvement ( Hayward et al., 1993 ; Meru, 2012 ; Wu et al., 2011 ). Both fruit and seed
achieved by chromosome doubling, and the progenies of these synthetic amphidiploids were studied for selection of economic types ( Ali et al., 1992 ; Isshiki et al., 2000 ; Rajasekaran, 1970 , 1971 ; Toppino et al., 2008a , 2008b ). However, chromosome
of only one ploidy level. Alternatively, additional concentrations and treatment times or sizes of explants could be evaluated because these can affect the percent of meristem cells successfully doubled and penetration of the chromosome-doubling agent
simplex Wright ( Freyre et al., 2012 ). The key step in ploidy manipulation is chromosome doubling and induction of stable tetraploids, which are the gateway to obtain other ploidy levels (triploids, pentaploids, hexaploids, octoploids, etc.) through
indicating limited female fertility from either selfing or apomixis. Chromosome doubling to restore fertility to sterile-wide hybrids has been used with varying success. Contreras et al. (2007) reported an increase in pollen staining from 0% to 68% and an
vitro chromosome doubling was successful, and the combination of oryzalin (15 μM) with nitrotyrosine (50 μM) yielded the greatest frequency of induced polyploids for both ‘Robert’ and ‘MAK20’. Although the effect of induced autotetraploidy varied by
( Hättenschwiler and Körner, 2003 ). In attempts to address shot-hole symptoms and the weedy tendencies in this species, we created chromosome doubled forms of the cultivar Schipkaensis. Although many studies have compared morphological variability in ploidy series
A high priority in rose (Rosa spp.) breeding research is the transfer of disease resistance, especially to black spot (Diplocarpon rosae Lib.), from wild diploid Rosa species to modern rose cultivars. To this end, amphidiploids (2n = 4x = 28) were induced with colchicine from five interspecific diploid (2n = 2x = 14) hybrids involving the black spot resistant diploid species R. wichuraiana Crép, R. roxburghii Thratt., R. banksiae Ait., R. rugosa rubra Hort., and R. setigera Michaux. Two application procedures (agitation of excised nodes in colchicine solution or tissue culture of shoots on medium with colchicine), five colchicine concentrations (0.0, 1.25, 2.50, 3.76, and 5.01 mmol), and five durations (2, 3, 5, 8, and 10 d) were used. After colchicine treatment, the materials were cultured in vitro and the surviving explants were examined for the “gigas” characteristics typical of doubled diploids. Chromosome counts of morphologically suspect genotypes confirmed 15 amphidiploids among 1109 plants that survived colchicine treatment. Although the effect of colchicine treatment varied some among interspecific hybrids, 2.50 mmol for 48 h of node agitation or 1.25 mmol for at least 5 d of shoot culture were optimal.
To produce the homozygous strain of a haploid plant derived from small seed-derived seedlings of `Banpeiyu' pummelo (Citrus grandis Osbeck), we carried out colchicine treatment to axillary shoot buds of the haploid. Many shoots with cytochimeras (X+2X and 2X+4X) arose from the colchicine-treated axillary buds. When cytochimeric buds of 2X+4X were top-grafted onto trifoliate orange [Poncirus trifoliata (L.) Raf.], a complete diploid shoot with 18 chromosomes was obtained from the cytochimera. This diploid strain showed vigorous growth compared with the original haploid. The leaf weight per unit area and the stomata size in this diploid were significantly larger than those of the original haploid plant, and were almost equal to those of `Banpeiyu' pummelo. The diploid strain was confirmed to be a doubled haploid of a haploid from `Banpeiyu' pummelo, based on random amplified polymorphic DNA (RAPD) analysis and chromosome composition analysis by chromomycin A3 (CMA) staining.