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Orlando McMeans and Robert M. Skirvin

To isolate unique fruit colors and look for somaclonal variation among regenerants, a regeneration protocol was established for various cultivars of striped apples (`Mailing 26', `Mutsu', `Regal Gala', `Summerland Red', and `Fuji'). Leaves were harvested from in m-grown plants, transferred to regeneration media [MS + NAA (5.4 μM) + TDZ (3 μM)], stored in the dark for 3 to 4 weeks, then moved to controlled light conditions, where adventitious shoot regeneration was observed. Developing shoots were transferred to proliferation medium and screened for their red or green phenotype by placing them on MS media containing various concentrations of sucrose (30, 45, 60, 75 and 90 g\L) and BA (0, 2.5, 5, 7.5, 10, 12.5 and 15 μM). Some of the regenerated apple shoots exhibited red color soon after being taken from the dark treatment. Others were less distinct, with colors ranging from dull green to a green-pink mixture. The red and green shoots are now being rooted and will be transferred to the field, where they will be grown to maturity.

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Mushtaq Sarwar and Robert M. Skirvin

Adventitious shoots were regenerated from apple (`Wijcik', `McIntosh', `Macspur', `M-26' and `Mutsu') by excising leaves from in vitro-grown shoots, cutting them into three sections, and plating them onto regeneration media. Cultures were kept in the dark for 1 to 4 weeks and then moved to light for further shoot development. MS medium supplemented with thiadiazuron (2-3 μM) and napthaleneacetic acid (5 μM) produced the highest number of shoots per leaf segment. `Wijcik' and `M-26' regenerated best from big leaves, whereas `McIntosh' and `Macspur' regenerated best from small leaves. Shoot formation was enhanced by 3 to 4 weeks of dark treatment and by placing the leaf on medium with its abaxial surface uppermost. The cut surface of leaf segments produced the most regeneration sites. In vitro adventitious shoots were transferred to various concentrations of BA (5, 10, 15, 20, 25 and 30 μM to screen them for BA tolerance and to predict their adult growth habit. These shoots will be rooted and transferred to greenhouse and field conditions for long-term evaluations.

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Ken McPheeters and Robert M. Skirvin

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Margaret A. Norton and Robert M. Skirvin

Rubus laciniatus Willd. `Thornless Evergreen' (TE) is a chimeral blackberry with a thornless epidermis that overlies a genetically thorny interior. Most canes of TE produce leaves with 5 finely cut (lacinate) leaflets. Occasionally, canes appear which produce leaves with entire leaflets. Genetically pure thornless plants were regenerated from epidermal cells of chimeral TE with lacinate leaves. These regenerants exhibited somaclonal variation for growth habit, degree of thornlessness, and fruitfulness. All had lacinate leaves. When moved to the field, some of these regenerants produced canes with entire leaflets.

To examine the stability of the entire leaflet characteristic, plants were regenerated from lacinate leaves and entire leaves of both dwarf and normal pure thornless TE regenerants. Regenerants were rooted, moved to soil, and grown in the greenhouse for observation. Stability of this characteristic will be discussed.

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Renee M. Schloupt, Walter E. Splittstoesser, and Robert M. Skirvin

The objective of this research was to induce vitrification in onion (Allium cepa L. cv. `White Ebeneezer'); then use this information to make suggestions on how to avoid vitrification of micropropagated plants. There were no differences in vitrification percentage when shoot tip explants were isolated, sterilized and placed on MS medium (8 g.L-1 agar) supplemented with 0.16 uM NAA and varying (0.0 to 70.0 uM) levels of BA. When agar was replaced by gelrite (MS medium with 4.4 uM BA and 0.16 uM NAA), vitrification increased when gelrite concentrations decreased from 2.0 to 1.0 g.L-1. More vitrification occurred when shoot tips were supported on a synthetic cosmetic puff in liquid medium or when agar was reduced to 4.0 g.L-1 than when supported on a cosmetic puff in 8 g.L-1 agar or on 8 g.L-1 agar alone.

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Nawab Ali, Robert Skirvin, Walter E. Splittstoesser, and William L. George

Cucumber (Cucumis sativus L.) seeds of `Marketer', `Marketmore', `Wisconsin SMR-18', `Tablegreen', `Spotfree', and `China' were stored at 3C and 38% relative humidity for up to 26 years. Seed older than 13 years did not germinate. Cultivars stored 10 years gave 80% germination, except Wisconsin SMR-18' (40%). Ten-year-old seeds were separated from their seedcoats, and cotyledons were excised into six segments. Explants were placed on Murashige and Skoog medium with all combinations of BAP (0, 1,2, and 3 mg·liter-1) and NAA (0, 0.1,0.2, and 0.3 mg·liter-1). Plants were obtained from culture for all cultivars grown on medium containing NAA and 1 mg BAP/liter. No plants were regenerated when BAP or NAA was lacking. Chemical names used: benzylaminopurine (BAP), 1-naphthaleneacetic acid (NAA).

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Nawab Ali, Robert M. Skirvin, and Walter E. Splittstoesser

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Karim Al-Juboory, Robert M. Skirvin, and David J. Williams

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Robert M. Skirvin, Kenneth D. McPheeters, and Margaret Norton

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Nawab Ali, Robert M. Skirvin, Walter E. Splittstoesser, David E. Harry, and William L. George

Seed lots with the genetic background of `Baroda' and `Marketer' cucumber (Cucumis sativus L.) containing all possible combinations (DF Df, Dfdf, dfdf) of df (which increases dormancy) and Df (wild type) were used. Dormancy was not solely due to the genotype dfdf and clear effects of genetic background were apparent. The df allele in the homozygous state induced a strong dormancy in `Baroda', but the Df gene could not restore normal germination. However, Df did reduce the dormancy period to 85 days. In `Marketer', df did not delay germination. Any treatment (puncturing, removal, cutting) that damaged the inner integument allowed `Baroda' dfdf to germinate, indicating an intact integument was essential for maintaining dormancy in this cultivar. All `Baroda' dfdf embryonic axes without the cotyledons germinated in 5 days. `Baroda' dfdf seeds with intact integuments imbibed adequate water to germinate but remained dormant, suggesting that the effect of the integument on dormancy was not related to imbibition.