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Jude W. Grosser, Hyun Joo An, Milica Calovic, Dong H. Lee, Chunxian Chen, Monica Vasconcellos and Frederick G. Gmitter Jr

hybrids recovered from crosses of mandarin with autotetraploid sweet oranges ( Gmitter et al., 1991 ) or the mentioned somatic hybrids have recently begun to fruit, and although several have exhibited good fruit quality, most are difficult to peel. This is

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Jude W. Grosser, Divya Kainth and Manjul Dutt

commonly used to induce tetraploidy in breeding lines in Citrus . Early attempts to generate autotetraploids by treating the axillary buds with colchicine ex vitro were performed by Barrett (1974) in monoembryonic cultivars. However, his technique did

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Jessica Gaus Barb, Dennis J. Werner and Shyamalrau P. Tallury

autotetraploid forms of diploid cultivars were produced using colchicine [N-(5,6,7,9-tetrahydro-1,2,3,10-tetra-methoxy-9-oxobenzo(a)heptalen-7-yl)acetamide] or oryzalin (3,5-dinitro- N 4 N 4 -dipropylsulfanilamide). Small (2.5 cm diameter) asexually reproduced

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Kelly M. Oates, Thomas G. Ranney and Darren H. Touchell

morphological responses vary ( Horn, 2002 ). Furthermore, autotetraploids may also have a slower growth rate compared with their diploid cytotypes ( Chahal and Gosal, 2002 ). A greater understanding of the influence of induced polyploidy on fertility and

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Grace M. Pietsch and Neil O. Anderson

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.

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Jude W. Grosser, Frederick G. Gmitter Jr., E.S. Louzada and J.L. Chandler

Allotetraploid somatic hybrid plants of `Nova' tangelo [a sexual hybrid of `Clementine mandarin (C. reticulata Blanco) × `Orlando' tangelo (C. reticulata × C. paradisi Macf.)] + `Succari' sweet orange (C. sinensis L. Osbeck), and `Hamlin' sweet orange (C. sinensis L. Osbeck) + `Dancy' tangerine (C. reticulata) were regenerated following protoplast fusion. `Nova' and `Hamlin' protoplasts were isolated from ovule-derived embryogenic callus and suspension cultures, respectively, and fused using a polyethylene glycol method with seedling leaf-derived protoplasts of `Succari' and `Dancy', respectively. Plants were regenerated via somatic embryogenesis, and somatic hybrids were identified on the basis of leaf morphology, root-tip cell chromosome number, and electrophoretic analysis of peroxidase and phosphoglucose mutase isozyme banding patterns. Diploid plants were regenerated from unfused protoplasts of `Hamlin', `Nova', and `Succari'. Tetraploid plants of `Hamlin' and `Succari' were also recovered, apparently resulting from homokaryotic fusions. No `Dancy' plants were recovered. The somatic hybrid and autotetraploid plants can be used for interploid hybridization with selected monoembryonic scions to generate improved seedless triploid tangor/tangelo cultivars. The lack of suitable tetraploid breeding parents has previously inhibited the development of quality seedless cultivars by this method.

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Zenaida Viloria and Jude W. Grosser

Interploid hybridization was conducted using `Key' lime [Citrus aurantifolia (Cristm.) Swing.], `Lakeland' limequat hybrid [C. aurantifolia × Fortunella japonica (Thumb.) Swing.], Palestine sweet lime (C. limettioides Tan.), `Etrog' citron (C. medica L.), and seven lemon [C. limon (L.) Burm. F.] varieties as female progenitors and five allotetraploid somatic hybrids {`Hamlin' sweet orange [C. sinensis (L.) Osbeck] × `Femminello' lemon (C. limon)]; `Key' lime × `Valencia' sweet orange (C. sinensis); `Valencia' sweet orange × rough lemon (C. jambhiri Lush); Milam lemon (purported C. jambhiri hybrid) × `Femminello' lemon (C. limon); and `Valencia' sweet orange × `Femminello' lemon} and two autotetraploids [`Giant Key' lime (C. aurantifolia) and `Femminello' lemon] as pollen progenitors. A few tetraploid × diploid crosses were also performed. Thirty-five parental cross combinations were accomplished in 2000, 2001, and 2002. The breeding targets were seedlessness, cold-tolerance, and disease resistance. Triploid hybrids were recovered through embryo culture. Generation of triploid citrus hybrids was affected by several factors including sexual compatibility, cross direction, embryo developmental stage, pollen viability, as well as horticultural practices and climatic conditions. Efficiency of triploid hybrid production was higher in diploid × tetraploid crosses than the reciprocal. Many more triploid hybrids were generated from lemon seed progenitors compared to the other acid citrus fruit progenitors. `Todo el Año', `Lisbon', and `Limonero Fino 49' showed the highest sexual compatibility. Embryo germination rate and normal plant recovery were also higher in lemons as compared to the other seed progenitors. Low winter temperatures might have affected the hybrid production efficiency from tropical acid fruit progenitors. A total of 650 hybrids (mostly triploid) were transferred to soil. The novel genetic combinations of these progenies should be valuable for the genetic improvement of acid citrus fruit (lemons and limes).

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Malcolm W. Smith, Jeremy D. Bright, Mark D. Hoult, Richard A. Renfree, Tony Maddern and Neil Coombes

has not changed. Thus, there may be some value in developing and screening autotetraploids of superior mango rootstock genotypes in the hope of reducing vigor while retaining other superior characteristics. The time and cost involved in long

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Richard T. Olsen, Thomas G. Ranney and Dennis J. Werner

Inheritance of two mutant foliage types, variegated and purple, was investigated for diploid, triploid, and tetraploid tutsan (Hypericum androsaemum). The fertility of progeny was evaluated by pollen viability tests and reciprocal crosses with diploids, triploids, and tetraploids and germinative capacity of seeds from successful crosses. Segregation ratios were determined for diploid crosses in reciprocal di-hybrid F1, F2, BCP1, and BCP2 families and selfed F2s with the parental phenotypes. F2 tetraploids were derived from induced autotetraploid F1s. Triploid segregation ratios were determined for crosses between tetraploid F2s and diploid F1s. Diploid di-hybrid crosses fit the expected 9: 3: 3: 1 ratio for a single, simple recessive gene for both traits, with no evidence of linkage. A novel phenotype representing a combination of parental phenotypes was recovered. Data from backcrosses and selfing support the recessive model. Both traits behaved as expected at the triploid level; however, at the tetraploid level the number of variegated progeny increased, with segregation ratios falling between random chromosome and random chromatid assortment models. We propose the gene symbol var (variegated) and pl (purple leaf) for the variegated and purple genes, respectively. Triploid pollen stained moderately well (41%), but pollen germination was low (6%). Triploid plants were highly infertile, demonstrating extremely low male fertility and no measurable female fertility (no viable seed production). The present research demonstrates the feasibility of breeding simultaneously for ornamental traits and non-invasiveness.

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Jin-Hu Wu, A. Ross Ferguson, Brian G. Murray, Alison M. Duffy, Yilin Jia, Canhong Cheng and Philip J. Martin

Actinidia chinensis with those of fruit from autotetraploids produced by colchicine-induced chromosome doubling. Our aim was to determine the effects of increasing the number of genomes on fruit quality and development using a number of easily measured