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Open access

R. J. Henny

Abstract

Autotetraploid (4n) plants of Dieffenbachia maculata (Lodd.) G. Don ‘Perfection’ flowered poorly, compared to diploids (2n), following treatment with 250 or 500 mg foliar spray of gibberellic acid (GA3)/liter. GA3-treated 4n plants produced bracts that normally precede flowering but remained vegetative and produced additional distal shoots instead of flowers.

Free access

Henry R. Owen and A. Raymond Miller

A comparison of pretreatment, fixing, and staining methods for root tips of Fragaria × ananassa (2n=8x=56), a polyploid species with small chromosomes, was made to facilitate chromosome counting. Three pretreatments (8-hydroxyquinoline, α-bromonaphthalene, and p-dichlorobenzene), three fixatives (Farmer's, Carnoy's, and Newcomer's), and five stains (acetocarmine, lacto-propionic orcein, leucobasic fuchsin, altered carbol fuchsin, and alcoholic hydrochloric-acid carmine) were examined in a factorial design to determine which treatment combination produced the best chromosome preparation. Field propagated runners were grown in sand under greenhouse conditions with supplemental lighting to produce root tips for late morning collection. The treatment combinations of α-bromonaphthalene or 8-hydroxyquinoline, Farmer's fixative, and altered carbol fuchsin, or the combination of α-bromonaphthalene, Farmer's fixative, and alcoholic hydrochloric-acid carmine produced the most intensely-stained and well-defined preparations.

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Rengong Meng, Chad E. Finn, and Robert P. Doss

Knowledge of the chromosome number in Rubus would be valuable when planning crosses and identifying plants, etc., however, preparation of tissue for microscopic evaluation and chromosome counting is difficult and time-consuming. Flow cytometry offers a more-efficient approach to this task. DNA flow cytometry was used to determine the nuclear DNA content in 22 Rubus genotypes. The genotypes represented a range of reported chromosome numbers from 2x to 12x. Six of the genotypes were representatives of Rubus ursinus, which is reported to have both 8x and 12x forms. Samples of nuclei were prepared from leaf discs of newly emerged and mature leaves following published protocols with some modifications. The DNA content was estimated by comparison of the fluorescence of Rubus nuclei with an internal DNA standard. There was an increase in nuclear DNA content concurrent with the increase in chromosome number. In these studies DNA flow cytometry could differentiate genotypes that differed by 2x, such as 6x and 8x, but could not reliably distinguish genotypes that differed by 1x, such as 7x vs. 8x or 6x. Aneuploids cannot be differentiated at this time.

Open access

Patricia Cole and Bill Melton

Abstract

The breeding of hybrid rose cultivars is part of the ornamental rose industry, but there have been few studies concerned with the factors limiting reproduction in the genus Rosa L. In this study, 28 species of Rosa were examined under field conditions for self- and cross-compatibility relationships. Twenty-five specimens of 25 species were tested for self-compatibility. All of the 23 diploid plants tested exhibited more than 96%. Twelve of the 16 polyploid plants preserved the 96% self-incompatibility reaction. A distinct separation existed between self-compatible and self-incompatible polyploid plants. Four of the 5 diploid cross-fertilizations produced unexpected reciprocal differences. Significant reciprocal differences were not obtained from the polyploid level cross-fertilizations. Some parthenocarpy occurred in the R. stellata species. Pollen viability and abundance, daily maximum and minimum temperature, and maximum and minimum relative humidity were not correlated with the compatibility reactions.

Free access

Carol Gonsalves, Baodi Xue, Marcela Yepes, Marc Fuchs, Kaishu Ling, Shigetou Namba, Paula Chee, Jerry L. Slightom, and Dennis Gonsalves

A single regeneration procedure using cotyledon explants effectively regenerated five commercially grown muskmelon cultivars. This regeneration scheme was used to facilitate gene transfers using either Agrobacterium tumefaciens (using `Burpee Hybrid' and `Hales Best Jumbo') or microprojectile bombardment (using `Topmark') methods. In both cases, the transferred genes were from the T-DNA region of the binary vector plasmid pGA482GG/cp cucumber mosaic virus-white leaf strain (CMV-WL), which contains genes that encode neomycin phosphotransferase II (NPT II), β-glucuronidase (GUS), and the CMV-WL coat protein (CP). Explants treated with pGA482GG/cpCMV-WL regenerated shoots on Murashige and Skoog medium containing 4.4 μm 6-benzylaminopurine (BA), kanamycin (Km) at 150 mg·liter-1 and carbenicillin (Cb) at 500 mg·liter-1. Our comparison of A. tumefaciens- and microprojectile-mediated gene transfer procedures shows that both methods effectively produce nearly the same percentage of transgenic plants. R0 plants were first tested for GUS or NPT II expression, then the polymerase chain reaction (PCR) and other tests were used to verify the transfer of the NPT II, GUS, and CMV-WL CP genes. This analysis showed that plants transformed by A. tumefaciens contained all three genes, although co-transferring the genes into bombarded plants was not always successful. R1 plants were challenge inoculated with CMV-FNY, a destructive strain of CMV found in New York. Resistance levels varied according to the different transformed genotypes. Somaclonal variation was observed in a significant number of R0 transgenic plants. Flow cytometry analysis of leaf tissue revealed that a significant number of transgenic plants were tetraploid or mixoploid, whereas the commercial nontransformed cultivars were diploid. In a study of young, germinated cotyledons, however, a mixture of diploid, tetraploid, and octoploid cells were found at the shoot regeneration sites.

Free access

Kim D. Bowman, Frederick G. Gmitter Jr., Gloria A. Moore, and Russell L. Rouseff

Citrus fruit with sector chimeras were collected in commercial packinghouses and from the field. Chimeric fruit from eight cultivars of sweet oranges [Citrus sinensis (L.) Osbeck], grapefruit (C. paradisi Macf.), tangelo (C. paradisi × C. reticulate Blanco), and tangors (C. reticulate × c. sinensis) were found at a frequency of 0.009% to 0.271%. Tetraploid plants obtained from one type of sector mutant (termed gigas) and albino plants obtained from another type of sector mutant confirmed that some genetic mutations observed in fruit rind can be recovered in nucellar seedlings. The gigas chimeras were identified as a source of citrus tetraploids. Several types of potentially useful sector mutants with altered rind color were observed, and plants were produced from some mutant sectors by developed seed or culture of aborted ovules. HPLC analysis of rind tissues from sectors of one chimeric fruit revealed substantial quantitative and qualitative differences in pigment composition. Propagation of plants from mutant sectors may yield cultivars with improved fruit color, altered maturation date, and reduced disease or mite susceptibility and may eventually lead to breeding of seedless triploid hybrids.

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Wenhua Lu, J.V. Edelson, Jim A. Duthie, and B. Warren Roberts

Factors of crop management such as irrigation, cultivation, cultivar selection, and control of insect pests and plant diseases play important roles in watermelon production. To gain a better understanding of how intensity of crop management affects yield, we conducted a comparative study contrasting high and low intensity management in 1997, 1999, and 2000. High-intensity management (HM) included the use of trickle irrigation, black plastic mulch, insecticides, and fungicides, not used under low-intensity management (LM). We examined the effects of management intensity on watermelon productivity, the variation in such effects among watermelon cultivars, and the mediating effect of survival of watermelon plants, abundance of insect pests, and incidence of anthracnose (% leaves with anthracnose lesions). The results indicated that HM produced 100% greater marketable fruit yield per area and marketable fraction of total fruit than LM in 2 out of 3 years. The effect of management intensity on plant survival was related to this effect on yield in 1 out of 2 years, and contributed to the latter by increasing weight and number of marketable fruit per plant under HM. We detected no significant effect of abundance of insect pests and incidence of anthracnose on yield. There was variation in the effect of management intensity on yield among watermelon cultivars in 1 out of 3 years. The triploid `Gem Dandy' showed great differences in yield between HM and LM in 2 years, producing on average 28.9 Mg·ha-1 of marketable fruit yield under HM compared to 14.0 Mg·ha-1 under LM. `Gem Dandy' also produced 100% higher yield of marketable fruit per area, per plant, and marketable fraction of total fruit than the open-pollinated diploid `Allsweet' or the diploid hybrid `Sangria.' Each year during the 3-year study, all three cultivars had a similar density of insect pests, incidence of anthracnose, and plant survival after transplant and at harvest. This study provided information on the collective impact of multiple aspects of watermelon management on yield.

Open access

J. de Jong and W. Rademaker

Abstract

Dendranthema pacificum Nakai (Chrysanthemum pacificum Nakai; 2n = l0x = 90 chromosomes), a species native to Japan, was crossed to Dendranthema grandiflora Tzvelev (C. morifolium Ramat.; 2n = 6x = 54), the florist chrysanthemum, to develop a type with numerous small flowerheads. The first-generation hybrid was fertile, but the flowerheads were too small. In the first backcross to D. grandiflora, the desired type was obtained. The backcross (2n = 7x = 63) was very fertile, despite the odd number of genomes. D. pacificum may also be used as a source of resistance to the serpentine leaf miner (Liriomyza trifolii).

Free access

Irene E. Palmer, Thomas G. Ranney, Nathan P. Lynch, and Richard E. Bir

, there is little information available on ploidy levels of specific cultivars. Pseudogamy, a form of apomixis, has also been implicated as the sole means of reproduction in triploid R. triloba ( McCrea, 1981 ). A greater understanding of reproductive

Free access

Hamidou F. Sakhanokho, Kanniah Rajasekaran, Rowena Y. Kelley, and Nurul Islam-Faridi

, pharmaceutical, and agricultural improvement of plants ( Ascough et al., 2008 ). For instance, increased ploidy level was associated with increased flower size in rhododendrons and intensified flower colors in carnation and cyclamen ( Takamura and Miyajima, 1996