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  • Author or Editor: R.M. Skirvin x
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S. Sriskandarajahi and R.M. Skirvin

Extensive root development was observed on Stage 2 `Red Emerald' philodendron shoots grown on standard multiplication medium consisting of Murashige and Skoog salts and vitamins with 6-benzylaminopurine (BA, 0.2 mg·liter-1. Root development was suppressed significantly when the level of NH4NO3 was doubled from standard levels (lx, 1650 mg·liter-1) to 3300 mg·liter-1 (2×). A higher level of NH4NO3 (3×, 4950 mg·liter-1) was detrimental to shoot growth and proliferation. This information may be useful for commercial propagators who wish to suppress root development at the shoot multiplication stage.

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R.M. Skirvin and S. Sriskandarajah

Acclimatization and growth of in vitro-derived apple shoots of two apple scion apple cultivars were compared under fogged conditions in a greenhouse and in a commercial growth cabinet (Phototron). Plant survival rates of microcuttings of `Royal Gala' and `Jonagold' were significantly better when maintained in the Phototron units than when grown in a greenhouse under fog. The number and length of roots on microcuttings was significantly higher in the Phototron than under fog. In the present study, we demonstrated that the Phototron environment was better than a fogged greenhouse for establishing apple shoots ex vitro. However, the Phototron units are so small that they hold no more than 100 to 120 plants at a time. Therefore, the units will be of most value to growers or individuals in laboratories who do not have a constant need for acclimatization facilities. Growers who acclimatize many plants should continue to use fogging or misting facilities.

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M.A. Norton and R.M. Skirvin

A method has been developed for micropropagation of the difficult-to-root winegrape cultivar `Norton' (Vitis aestivalis). Plants were established in vitro from axillary bud cuttings of field-grown plants. Four levels of 6-benzylaminopurine (BA) and three levels of naphthaleneacetic acid (NAA) were tested in a factorial arrangement for their effectiveness in promoting multiplication of shoots from single-node explants. Three levels of NAA and two concentrations of Murashige and Skoog (MS) basal medium were tested for their effectiveness in promoting rooting of shoot tips. The greatest number of shoots per axillary bud in combination with the greatest shoot length were produced with 4 μmol·L-1 [0.90 mg·L-1 (ppm)] BA. NAA had no effect on shoot multiplication. NAA was not required for in vitro rooting. All rooted plants survived the transition to soil.

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M.A. Norton and R.M. Skirvin

Chimeral `Thornless Evergreen' (CTE), (Rubus laciniatus Willd.) somaclones selected in 1983 and field planted in 1985 were reexamined in 1992 for various vegetative and reproductive characteristics. Two major types of thornless (prickle-free) plants, intermediate-sized (`UI 6-6' = `Everthornless') and dwarf (`UI 6-4'), originally selected from a chimeral thornless parent plant, were compared with thorny plants. The intermediate and dwarf somaclones have maintained their distinctive habits over 7 years' growth in the field, indicating that their growth habits are stable and not a transient effect of tissue culture. Although the thornless somaclones remained thornless, the degree and type of prickle-like structures varies considerably, indicating that the thornless gene (S te) does not entirely suppress the production of prickles, but apparently alters their development. Increasing suppression was directly related to increasing dwarfism, suggesting a link between thornlessness and internode length.

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W. Msikita, H.T. Wilkinson and R.M. Skirvin

`Embryonic axes-derived `Burpless Hybrid' cucumber (Cucumis sativus L.) plantlets germinated on Murashige and Skoog (MS) medium supplemented with 16 combinations of BAP and NAA and seedlings derived from whole seeds cultured on semi-solid agar were inoculated in vitro with two isolates (WFU3 and WFM13) of Pythium aphanidermatum. All axes-derived plantlets and whole seedlings inoculated with WFM13 isolates were susceptible to blight and died 2 days after inoculation. Similarly, all seedlings inoculated with WFU3 isolates were killed within 2 days after inoculation; however, the rate of development and severity of blight varied among the axes-derived plantlets. Blight on axes-derived plantlets, regenerated on MS medium supplemented with 2 mg BAP/liter and 0.2 mg NAA/liter, was significantly less than on regenerants cultured on all other amended MS media. On some media, callus developed on crowns and/or primary roots. The presence of callus influenced resistance to Pythium. In a second experiment, axes-derived cucumber regenerants from five genotypes, cultured on MS medium supplemented with 2 mg BAP/liter and 0.2 mg N&A/liter, were compared for their resistance to P. aphanidermatum isolate WFU3. Resistance was significantly greater for `Burpless Hybrid' and `Sweetslice' than for three other genotypes. Chemical names used: 6-benzylaminopurine (BAP); α -naphthaleneacetic acid (NAA).

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K.H. Al-Juboory, D.J. Williams and R.M. Skirvin

Shoots of greenhouse-grown Algerian ivy (Hedera canariensis L.) were surface disinfected and explanted on modified Murashige and Skoog (MS) medium supplemented with BA (10 μm) and NAA (2.5 μm). One month later the shoots were transferred to MS proliferation medium supplemented with TDZ (0.1 or 0.5 μm) and NAA (40 μm). An average of three microshoots developed on each stem treated with TDZ. Pruned shoots grown on MS medium supplemented with GA3 (20 μm) and BA (20 μm) branched better than unpruned shoots (3.7 vs. 1 per explant, respectively). Rooted shoots grown ex vitro grew and developed a shape suitable for commercial sale in 3 months. Chemical names used: N -(phenyl-methyl)-l H -purine-6-amine (BA); gibberellic acid (GA3); 1-naphthaleneacetic acid (NM); N -phenyl-W-1,2,3-thiadiazo-5-yl urea (Thidiazuron, TDZ).

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W. Msikita, H.T. Wilkinson and R.M. Skirvin

A system to propagate tronchuda (Brassica oleracea var. tronchuda Bailey syn. costata L.) from main stem and side shoot cuttings was developed by removing the main stem (three to four leaves) and, later, side shoots from S-week-old plants, transplanting them into small pots, and growing them under a mist system for 4 weeks. New root growth appeared on cuttings within 3 weeks. Rooting frequency varied among cultivars and explant types. For all cultivars, side shoot cuttings rooted better than main stem cuttings (99.7% vs. 84.8%). For all cultivars, seed-propagated plants and side shoot cuttings produced leaves with significantly higher fresh weight than the main stem cuttings for three of the five cultivars. The average number of leaves per plant for four cultivars was, however, not significantly affected by propagation method. Average leaf count and fresh weight per plant were significantly higher for `Portuguesa' than for `Ana Maria'. `Couve Penca'. `Vilinda', and `Penca de Chaves' for all three propagation sources.

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M.A.R. Mian, R.M. Skirvin, M.A. Norton and A.G. Otterbacher

To study the causes of low germinability in dried blackberry seeds, seeds harvested from fresh `Thornless Evergreen' (TE) blackberry (Rubus laciniatus Willd.) were either air-dried (12, 24, 36, 48, 60, 72, 96, or 120 hours) or explanted directly onto growth-regulator-free medium after bleach disinfestation. Seeds were either cut in half before explanting or kept intact. None of the intact seeds germinated. Fewer of the halved seeds dried 12 hours or more germinated than control (fresh moist) seeds (42.7% and 54.5%, respectively). Germination decreased to <12% following >48 hours of air-drying. In a separate study, fresh seeds of TE and `Navaho' were either dried as described or held in sealed petri dishes on moist filter paper (moist treatment) for up to 60 hours. After 60 hours, germination of dried seeds of both cultivars had decreased significantly; there was no significant change in germination percentage for moist seeds. Since moist halved seeds germinated well and dried halved seeds did not, the inability of dried blackberry seeds to germinate is due to more factors than just the hard seedcoat typical of the genus.

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Karim H. Al-Juboory, J. Al-Naimi, L.K. Al-Amiry, R. Shibli and R.M. Skirvin

Callus was initiated from leaves of Gladiolus cv. `Balady' on MS medium containing 1.0 mg/L NAA, 0.1 mg/L 2,4-D, and 0.5 mg/L kinetin. Organogenesis from callus was induced on medium containing 0.5, 1.0, 1.5, or 2.0 mg/L of either BA, kinetin, or TDZ. TDZ was more effective and resulted in a higher percentage regeneration and regenerant number. The microshoots produced were then propagated in vitro and cormel production was studied. Maximum shoot number (25.1) was obtained on medium containing 1.0 mg/L TDZ without auxin supplements in liquid shaking culture. In vitro cormel formation was significantly enhanced by B-9 and paclobutrazol. Increased sucrose concentration (4% to 5%) proved the most effective for cormel formation. Optimal dormancy break was obtained by storing cormels at 5°C for 1 month or by soaking them for 5 sec with 50 mg/L GA3. In-vitro rooting was achieved on solid medium containing NAA, IAA, or IBA, with higher root number recorded on NAA-treated cultures. Rooted microshoots were successfully acclimatized for ex vitro conditions and grown in the greenhouse. Plants produced from in-vitro propagation showed similar morphological characteristics of plants propagated by direct corm planting in the greenhouse.

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Y. Mohamed-Yasseen, T. L. Davenport, W. E. Splittstoesser and R. M. Skirvin

Bulb formation in vitro is considered to be advantageous over shoot formation. Bulbs were farmed in vitro from onion inflorescence explants cultured in bulb induction medium composed of Murashige and Skoog (MS) medium supplemented with 120 g/l sucrose and 5 g/l activated charcoal under long day photoperiod. Bulbs were also induced in the same medium from shoots which were first regenerated from onion inflorescences in MS alone or MS containing either 4.4 uM benzyladenine or 0.005, 0.01, 0.05, 01 0.1 uM of thidiazurone. This system of in vitro bulb formation obviates shoot elongation, rooting, and acclimatization steps normally required when shoots are regenerated.