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Claire Woodward, Lee Hansen, Fleur Beckwith, Regina S. Redman and Rusty J. Rodriguez

changes in the underlying plant DNA sequences and can be vertically transmitted between generations through seedcoats, these symbioses can be defined as epigenetic phenomena. Collectively, endophytes can have profound effects on the physiology, growth

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Mark H. Brand and Richard Kiyomoto

Tissue proliferation (TP) of Rhododendron sp. is characterized by basal tumors that often develop into numerous dwarf shoots. Growers need to know if the TP condition will recur in plants grown from normal-appearing cuttings collected from plants with TP tumors. Stem cuttings of seven cultivars were collected from stock plants with TP [TP(+)] and without TP [TP(–)] and rooted. Plants were grown in containers outdoors for 2 years and were then evaluated for tumor formation and other TP-related morphological symptoms. Shoots of TP(+) plants were either similar in length to shoots of TP(–) plants, or were shorter, as was the case for `Boule de Neige', `Catawbiense Album', and `Montego'. Plants grown from TP(+) cuttings of all cultivars had more leaves per growth flush than did plants grown from TP(–) cuttings. `Holden', `Montego', and `Scintillation' TP(+) leaves were narrower than leaves from TP(–) shoots and had greater length: width ratios. Leaves of TP(+) `Montego' and `Scintillation' plants were shorter and smaller than leaves from their TP(–) counterparts. Tumors were not observed on any propagated plants, regardless of the TP status of cutting stock plants. To further test the influence of age and TP status of source plants used for cutting propagation, `Montego' plants were grown from cuttings collected from the following sources: 1) in vitro shoot cultures; 2) 3-year-old plants with TP; 3) 6-year-old plants with TP; and 4) TP(–) plants. Cuttings from TP(+) micropropagated plants less than 3 years old were more likely to develop tumors than were cuttings from older plants. Eighty-three percent of plants from microcuttings and 74% of plants from cuttings of 3-year-old TP(+) plants formed tumors, whereas no plants grown from 6-year-old TP(+) or TP(–) cuttings did so. Large tumors that surrounded half or more of the stem were more likely to develop on plants grown from microcuttings than on plants grown from the next youngest, 3-year-old TP(+), stock plants. Growers must be aware that cuttings from TP(+) plants may produce plants that exhibit morphological and growth abnormalities, possibly even including tumor redevelopment.

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Mark H. Brand, Yiqin Ruan and Richard Kiyomoto

To characterize the in vitro behavior of Rhododendron `Montego' with tissue proliferation (TP) to cytokinin and auxin, comparisons were made of normal [TP(–)], dwarf TP [TP(+) dwarf], and long TP [TP(+) long] shoot cultures. On basal medium TP(–) and TP(+), long shoots failed to multiply and had a low relative growth rate (RGR) of 0.1, whereas TP(+) dwarf shoots produced 31.8 shoots per tip, with most shoots being <5 mm long, and RGR was 0.3. Addition of 15 μm 2iP to basal medium induced the production of more than six shoots per TP(–) tip and doubled their RGR; TP(+) long shoots produced 16.8 shoots, most <5 mm long, and had an RGR of 0.3; TP(+) dwarf shoots produced only 16% as many shoots as on basal medium, but still exhibited an increase in RGR. Leaves from TP(–) and TP(+) sources failed to produce shoots on basal medium, but 74% of TP(–) leaves formed shoots when cultured on 1 μm IBA and 30 μm 2iP. TP(+) leaves were able to form shoot meristems on media containing only 5 μm 2iP (26% of explants), but these meristems failed to elongate into shoots. Calli from TP(–) leaves, TP(+) leaves, and TP(+) tumors grown on medium containing 10 μm NAA and 15 μm 2iP had higher RGRs than the same calli on basal medium during the first 8 weeks of culture. Over time, RGR decreased in both TP(–) and TP(+) leaf calli, but increased in TP(+) tumor callus. The increased RGR resulted from differentiation of shoot meristems on 85% of the calli between week 4 and week 8. Our results suggest that TP(+) tissues have altered hormone metabolism or sensitivity that leads to dramatic differences in in vitro behavior and probably contributes to tissue proliferation observed in whole plants. Chemical names used: 6-(γ,γ-dimethylallylamino) purine (2iP); indole-3-butyric acid (IBA); α-naphthaleneacetic acid (NAA).

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Seung Hee Eom and Tae Kyung Hyun

In eukaryotes, histone modifications, including acetylation, methylation, phosphorylation, ubiquitination, and glycosylation, are major epigenetic mechanisms that regulate numerous biological processes. Among these modifications, the acetylation of

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Adriana Telias, Emily Hoover and Diego Rother

single plants and even single spurs produced both kinds of fruits, a strictly genetic control of the trait can be ruled out. These results also indicated that the blushed/striped phenomenon is probably not chimeral. We speculate that an epigenetic

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David C. Zlesak and Neil O. Anderson

variation in initial bulb size, LSV titer (ROD), previous FC environment, and underlying genetic or epigenetic differences among grower lots. More work is warranted to better characterize the genetic or epigenetic differences among grower intraclonal strains

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

reviewed extensively and proposed mechanisms include both genetic (sequence deletions, rearrangements, subfunctionalization, gene repression and dominance, novel activation, dosage effects) and epigenetic factors (DNA methylation) ( Adams and Wendel, 2005

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Ren-jun Feng, Li-li Zhang, Jing-yi Wang, Jin-mei Luo, Ming Peng, Jun-feng Qi, Yin-don Zhang and Li-fang Lu

were down-regulated and putative myosin heavy chain was up-regulated by cold stress conditions ( Table 1 ). Methylation of proteins, nucleotides, and sugars is crucial for metabolism, cell signaling, and epigenetic programming, and a methyl group is

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Anna L. Hale, J. Creighton Miller Jr., K. Renganayaki, Alan K. Fritz, J.J. Coombs, L.M. Frank and D.S. Douches

The objective of this study was to differentiate six intraclonal variants of the potato (Solanum tuberosum L.) cultivar Russet Norkotah. One-hundred-twelve AFLP primer combinations producing 3755 bands and 79 microsatellite primers producing over 400 bands failed to identify any reproducible polymorphisms among the intraclonal variants and `Russet Norkotah'. The inability to detect differences between clones underscores the degree of genetic similarity between them, despite differences in phenotypic expression. This inability could be due to the tetraploid nature of the clones and/or to epigenetic differences not detected by the utilized procedures.

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Steve McCulloch

Briggs Nurseries, Inc. has used micropropagation as method of vegetative propagation for over 20 years. Genetic stability and uniformity of plants that are produced and sold is of the utmost concern to the commercial plant propagator. Genetic stability may be accomplished by ensuring that all shoots formed in vitro are of axillary origin and by reducing shoot proliferation rates through the use of lower cytokinin concentrations in the culture medium. Excision and removal of callus during transfer is also necessary to ensure that shoots develop from axillary buds. Various factors that may influence genetic variability and its frequency of in vitro derived plants will be discussed with an emphasis on how to reduce them. Three sources of variation with tissue culture derived plants will also be reviewed (Swartz, 1991): a) source plant variability, b) genetic changes in vitro, and c) epigenetic or physiological adaptation.