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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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Christopher S. Cramer

Determination of ploidy is an essential plant breeding technique. Laboratory exercises for teaching students how to determine ploidy in plant tissues using various techniques are described for geranium and onion. The different methods include root tip squashes, pollen mother cell squashes, pollen grain size and germinal pore counts, stomata size and density determination, and gross morphology.

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David C. Zlesak, Vance M. Whitaker, Steve George and Stan C. Hokanson

allow for cultivar ploidy determination using root tip squashes. Potted plants of cultivars were obtained in the summer of 2007 and maintained on an outdoor gravel pad. They were transferred to a cold room and provided with a 4 °C vernalization treatment

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Liuhui Yang, Jianjun Zhang, Jaime A. Teixeira da Silva and Xiaonan Yu

The karyotypes of 21 herbaceous peony (Paeonia) cultivars were studied using root tip squashes revealing a wide variety of ploidy levels. There were three tetraploid (2n = 4x = 20), 11 triploid (2n = 3x = 15), and one diploid (2n = 2x = 10) cultivars in the hybrid group; five triploid (2n = 3x = 15) cultivars in the Itoh group; and one diploid (2n = 2x = 10) cultivar in the lactiflora group (LG). The asymmetry index (AI) ranged from 59.61% (‘Cytherea’) to 64.03% (‘Little Red Gem’). The karyotypes of all peony cultivars were 2A with 60% metacentric (m), 20% submetacentric (sm), and 20% subtelocentric (st) chromosomes. The karyotypic background of these 21 herbaceous peony cultivars is discussed in the context of the evolution of ploidy and the three cultivar groups. These results provide cytological information that would assist in a peony hybridization program.

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Jessica Gaus, Dennis Werner and Shyamalrau Tallury

Segregation analysis of two different F2 families of stokes aster created by hybridizing two blue-flowered cultivars [`Peaches Pick' (PE) and `Omega Skyrocket' (OSR)] with the yellow-flowered cultivar `Mary Gregory' (MG) gave disparate results. The F2 progeny of PE × MG segregated in the expected 3:1 (blue:yellow) ratio. In contrast, all 782 progeny from the MG × OSR F2 family were blue-flowered. Flow cytometric analysis of the parents and F1 hybrids was conducted to determine if ploidy differences existed among the parents, as such differences could account for aberrant segregation behavior in the MG × OSR F2 family. Peak ratios suggested that MG and PE were diploid, OSR was tetraploid, and F1 hybrids of MG × OSR were triploid. Chromosome counts from root tip squashes confirmed that MG and PE were diploid (2n= 2x= 14), OSR was tetraploid (2n= 4x= 28), and F1 hybrid progeny of MG × OSR were triploid (2n= 3x= 21). Karyotype analysis also confirmed these results. We propose that the lack of recovery of yellow-flowered progeny in the MG × OSR F2 family is due to differences in parental chromosome number. These results document the first report of polyploidy in stokes aster, and suggest the absence of a triploid block in this species.

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Lincoln C. Peirce and Heather G. Miller

Several cinnamic acids have been identified as principal toxic components of asparagus (Asparagus officinalis L.) root autotoxin and have been shown to synergize Fusarium infection of asparagus. The basis for this synergism was studied by exposing asparagus seeds and radicles from pregerminated seeds to ferulic (FA), caffeic (CA), or methylenedioxycinnamic (MDA) acids alone and in combinations of two or three of these acids. After treatment, seeds were placed in pots of peat-lite mix, and, depending on the experiment, all or half were inoculated with F. oxysporum (Schlecht) f. sp. asparagi (Cohen). Seedling emergence from each pot was used as a measure of toxicity. All cinnamic acids at 1% suppressed emergence compared with the control. Solutions combining FA and CA (0.5%/0.5%, v/v) were substantially more toxic than 1% solutions of either alone. Exposure of radicles (early postgermination) for 10 minutes to combined FA/CA before planting decreased emergence from pots, whereas emergence following a 10-minute exposure to 1% CA or FA alone did not differ from the controls. The 2-hour exposure to FA or to FA/CA and the 24-hour exposure to CA, FA, or FA/CA decreased emergence, with toxicity progressing as follows: CA < FA < FA/CA. Root tip squashes showed fewer mitotic figures in treated than in untreated radicles, and scanning electron microscopic (SEM) examination of the radicle epidermis revealed damage to the surface of epidermal cells and precocious root hair development, the extent of which paralleled treatment toxicity.

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Kathy Zuzek, David Zlesak, Vance Whitaker, Steve McNamara and Stan C. Hokanson

. Prickles are slightly hooked and face downward. Northern Accents ® ‘Lena’, ‘Ole’, ‘Sigrid’, and ‘Sven’ were found to be diploid (2 n = 2 x = 14) when characterized for ploidy using root tip squashes and observing cells in metaphase ( Zlesak, 2009

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Ryan N. Contreras, Ron Determann and Mara Friddle

a genome size statistically different from the majority of cultivars in the study. However, cytological analysis revealed that it too is diploid ( Fig. 1C ). Fig. 1. Photomicrographs of chromosome spreads from root tip squashes of Cryptomeria

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Joseph J. Rothleutner, Mara W. Friddle and Ryan N. Contreras

chloroform : 1 glacial acetic acid (by volume)] overnight. Root tips were stored in 70% ethanol at 4 °C until prepared for chromosome counts ( Goldblatt and Gentry, 1979 ). Chromosomes were examined by root tip squashes with modified carbol fuchsin, at ×63 to

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Brian M. Schwartz, Ryan N. Contreras, Karen R. Harris-Shultz, Douglas L. Heckart, Jason B. Peake and Paul L. Raymer

metaphase I or anaphase I were observed to determine the chromosome number. The somatic chromosome numbers of ‘Sea Spray’, ‘SeaStar’, and 11-TSP-1 were also determined using root tip squashes collected from plants grown in pots filled with perlite. After a