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    C-banding analyses of Bromus inermis genomes
    (Wiley, 2004) Tuna, M; Vogel, KP; Gill, KS; Arumuganathan, K
    Smoothbromegrass (Bromus inermis Leyss.) has both tetraploid (2n = 28) and octaploid (2n = 56) ploidy levels that have been difficult to characterize cytogenetically because of similar chromosome morphology. Objectives of this study were to identify individual chromosomes of tetraploid and octaploid B. inermis with C-banding procedures along with chromosome length and arm length ratios, develop more detailed karyotypes than those previously available, and use the karyotypes to examine the genomic relationship of tetraploid and octaploid B. inermis. Root tips of the plants from four tetraploid and three octaploid accessions were used to produce chromosome squash preparations for cytogenetic analysis. The tetraploid B. inermis genome consisted of 12 chromosomes with a telomeric band on each arm and sixteen chromosomes with only one telomeric band on one arm. All of the chromosomes of the tetraploid form, except for four chromosomes, were identified by C-banding patterns, chromosome length, and arm length ratio. The octaploid B. inermis genome consisted of four chromosomes with no C-bands, approximate to14 chromosomes with two telomeric bands, and approximate to38 chromosomes with only one telomeric band on either the short or long arm. The combined use of C-banding, chromosome size, and arm length ratio only enabled groups of 2, 4, 6, or 8 similar chromosomes to be identified because of similarities in chromosome morphology of the octaploids. Results indicate that tetraploid B. inermis is an allotetraploid since all chromosomes except four could be separated into identifiable pairs. Because of differences between expected and actual numbers of satellite chromosomes and chromosomes with specific C-banding patterns, octaploid B. inermis is probably not a doubled form of the tetraploid B. inermis.
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    DNA content and ploidy determination of bromegrass germplasm accessions by flow cytometry
    (Wiley, 2001) Tuna, M; Vogel, KP; Arumuganathan, K; Gill, KS
    Species of the genus Bromus represent ploidy states from diploid to decaploid. Ploidy determination of Bromus germplasm is necessary before it can be effectively used in breeding or genetic studies. The objective of this study was to characterize the ploidy of 322 accessions of four Bromus species [Bromus inermis Leyss, B. riparius Rehm, B. biebersteinii Roem and Schult., and B. inermis ssp. pumpellianus (Scribn) Wagnon] that are in the USDA National Plant Germplasm System (NPGS). Flow cytometry was used to determine DNA content of 10 plants of each accession. Mean DNA contents were correlated to ploidy level with root tip chromosome counts on selected accessions whose DNA content indicated that they represented different ploidy levels. On the basis of DNA content (pg 2C(-1) = DNA content of a diploid somatic nucleus) and chromosome counts, mean DNA content and chromosome number was 22.62 pg 2C(-1) for octaplold B. biebersteinii (2n = 8x = 56), 26.07 pg 2C(-1) for decaploid B. biebersteinii (2n = 10x 70), 11.74 pg 2C(-1) for tetraploid B. inermis (2n = 4x = 28), 22.28 pg 2C(-1) for octaploid B. inerm is (2n = 8x 56). 22.72 pg 2C(-1) for octaploid B. inermis ssp. pumpellianus (2n 8x = 56). 26.5 pg 2C(-1) for decaploid B. inermis ssp.pumpellianus (2n = 10x = 70), 6.14 pg 2C(-1) for diploid B. riparius (2n = 2x = 14), 22.15 pg 2C(-1) for octaploid B. riparius (2n = 8x = 56), and 26.64 pg 2C(-1) for decaploid B. riparius (2n = 10x = 70). Standard deviations of the mean values were 0.88 pg 2C(-1) or less. Most B. inermis and B. inermis ssp. pumpellianus accessions were octaploid (93.75%), while the majority of the B. riparius and B. biebersteinii were decaploid (92.30%). The B. inermis and related species in the USDA NPGS were collected primarily from areas in the former USSR. The NPGS bromegrass germplasm could be enhanced by collections from western and central Europe, the Middle East, and China.
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    Karyotype and C-banding patterns of mitotic chromosomes in diploid bromegrass (Bromus riparius Rehm)
    (Wiley, 2001) Tuna, M; Gill, KS; Vogel, KP
    Previous cytogenetic studies of the genus Bromus L. were limited to chromosome counts and construction of karyotypes on the basis of Feulgen staining. Since the chromosomes of Bromus are similar in morphology, these karyotypes are of limited use for chromosome identification and genome analysis. The objectives of this study were to develop and evaluate a Giemsa C-banding procedure to use in identification of individual bromegrass chromosomes and to develop a karyotype for diploid Bromus riparius Rehm. (2n = 14; PI 440215). All chromosomes had one or more C-bands which were located mainly at telomeric regions. A group (I) of four pairs of chromosomes had telomeric bands on only one arm and could be differentiated. In this group, one pair had an interstitial C-band along with a telomeric band, one pair had a nucleolus organizer region (NOR) at a subtelomeric location on the short arm, and the other two pair could be distinguished by centromere location. The other group (II) of three pairs or chromosomes had telomeric bands on both arms. The unequivocal identification of specific chromosomes of Group II was not possible in all cells because of their similarity and differential condensation of chromosomes. Chromosomes of both groups were either metacentric or submetacentric. The total length of individual chromosomes ranged from 5.58 to 6.87 mum and the arm ratios ranged from 1.02 to 1.5. The homologous chromosomes were paired and assigned numbers I to VII in decreasing length. A karyotype was constructed by means of the C-bands, mean chromosome lengths, and arm ratios. The C-banding procedure used in this study could be used to developed karyotypes for the other species of the genus Bromus and these C-banded karyotypes could be used to compare genomes within the genus.