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James A. Kapaun and Zong-Ming Cheng

Plants were regenerated from leaf tissue of greenhouse-grown seedlings of Siberian elm (Ulmus pumila L.). Shoot regeneration was induced on Murashige and Skoog (MS) medium containing 5 to 10 μm of BA. Up to 55% of the leaf explants formed shoots with an average of 2.4 shoots per explant. Addition of 2.5 or 5 μm of IBA failed to enhance regeneration. Thidiazuron at 0.5 or 1.0 μm also induced shoot regeneration, but the shoots failed to elongate as well as shoots regenerated from media containing BA. Incubation in darkness for 7, 14, or 21 d had little effect in promoting shoot regeneration, except that incubation for 21 d increased shoot regeneration on the medium with 5.0 μm BA. Genotypes differed in shoot regeneration potential, with regeneration frequencies ranging from 13% to 55%. Regenerated shoots were micropropagated on Driver and Kuniyuki Walnut medium. Ninety percent of microcuttings rooted directly in potting soil. This regeneration system will be valuable for genetic transformation and cell selection of Siberian elm. Chemical names used: 6-benzylaminopurine (BA); indole-3-butyric acid (IBA); N-phenyl-N′ -1,2,3-thiadiazol-5-ylurea (thidiazuron, TDZ).

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Constance A. Parks and Thomas H. Boyle

The effects of stratification, BA, thiourea, and GA3 were examined on germination of Liatris spicata (L.) Willd. seed. Seeds were germinated at 20 °C and numbers of germinated seed were counted daily for 21 days. The final germination percentage (G) for seeds stored dry at 4 °C for 0 to 10 weeks ranged from 52% to 64%, while stratification at 4 °C for 10 weeks increased G to 98% and decreased the days to 50% of final germination (T50) and the days between 10% and 90% germination (T90-T10). Aqueous solutions of BA at 10 or 100 mg·L-1 applied to blotter paper increased G and decreased T50 but did not affect T90-T10. In a separate experiment, dry seeds were treated for 3 minutes in BA at 0 to 1126 mg·L-1 dissolved in acetone. G values increased quadratically, whereas T50 and T90-T10 values decreased quadratically in response to BA concentration. A 3-minute preplant acetone permeation of seeds with BA at 225 or 1127 mg·L-1 yielded G and T50 values similar to those obtained with 10 weeks of stratification. Seeds immersed in thiourea at 0.76 or 7.61 mg·L-1 for 24 hours prior to sowing had higher G and lower T50 values than controls (0 mg·L-1 thiourea), but T90-T10 values were similar for all treatments. Seeds treated with GA3 at 1, 10, or 100 mg·L-1 in H2O did not differ from controls (0 mg·L-1 GA3) in G, T50, or T90-T10. Infusion of BA via acetone may be a practical means of breaking seed dormancy and accelerating germination in L. spicata. Chemical names used: N-(phenylmethyl)-1H-purine-6-amine [benzyladenine (BA)]; gibberellic acid (GA3); thiocarbamide (thiourea).

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Anil P. Ranwala and William B. Miller

The effects of Promalin® [PROM; 100 mg·L–1 each of GA4+7 and benzyladenine (BA)] sprays on leaf chlorosis and plant height during greenhouse production of ancymidol-treated (two 0.5-mg drenches per plant) Easter lilies (Lilium longiflorum Thunb. `Nellie White') were investigated. Spraying with PROM at early stages of growth [36 or 55 days after planting (DAP)] completely prevented leaf chlorosis until the puffy bud stage, and plants developed less severe postharvest leaf chlorosis after cold storage at 4 °C for 2 weeks. When PROM was sprayed on plants in which leaf chlorosis had already begun (80 DAP), further leaf chlorosis was prevented during the remaining greenhouse phase and during the postharvest phase. PROM caused significant stem elongation (23% to 52% taller than controls) when applied 36 or 55 DAP, but not when applied at 80 DAP or later. The development of flower buds was not affected by PROM treatments. Although PROM sprays applied at 55 DAP or later increased postharvest flower longevity, earlier applications did not. Chemical names used: N-(phenylmethyl)-1H-purine 6-amine (benzyladenine, BA); α-cyclopropyl-α-(p-methoxyphenyl)-5-pyrimidinemethanol (ancymidol).

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Virginia M. Keith and Mark H. Brand

Significant occurrences of phenotypic variation have been noted in micropropagated Rhododendron. Studies were undertaken to determine what aspects of micropropagation lead to variation. Rhododendron `Molly Fordham' was used to evaluate growth parameters and the incidence of variation in plants that originated from 3 month and 54 month old cultures. Plants from 3-month-old cultures were significantly wider than plants from 54-month-old cultures. Rhododendron `Aglo', `Molly Fordham', and `Scintillation' were used to evaluate growth and the incidence of variation in plants grown from microcutting bases and rerooted microcutting tips (retips). Three-month-old retips were significantly taller and wider than bases of the same age, but possessed fewer branches. The influence of in vitro N6-[2-isopentenyl]adenine (2-iP) concentration on the growth and phenotype of regenerated plants of `Aglo', `Molly Fordham', and `Scintillation' was examined. Data taken 3 months post-acclimation indicate that growth and the incidence of variation in response to 2-iP concentration is cultivar dependent.

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Ryutaro Tao and Akira Sugiura

Callus cultures were initiated in the dark from leaf primordia, stem internodes, and young leaves of adult Japanese persimmon (Diospyros kaki L.) to induce adventitious buds. A high frequency of regeneration occurred on Murashige and Skoog medium (MS) with half the normal NH4NO3 and KNO3 concentration (1/2N) and containing 10 μm zeatin or 1 μm 4PU-30 in combination with 0.1 μm IAA, or MS(1/2N) medium containing 0.03 to 0.1 μ m IAA or 0.01 to 0.03 μm NAA combined with 10 μm zeatin. No significant differences in the capacity of regeneration were observed among the calli from different explant sources. Only eight of 16 cultivars formed adventitious buds on MS(1/2N) medium containing 10 μm zeatin and 0.1 μm IAA, with the percentage of explants forming adventitious buds ranging from 2% to 72%. Chemical names used: indole3-acetic acid (IAA); 1-naphthaleneacetic acid (NAA); N-phenyl-N'-(2-chloro-4-pyridyl)urea (4PU-30).

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O. Pérez-Tornero, F. Ortín-Párraga, J. Egea and L. Burgos

Apricot (Prunus armeniaca L. cv.'Helena') shoots grown on a proliferation medium containing 3% sucrose, 0.4 mg·L–1 benzyladenine (BA), and 0.04 mg·L–1 indolebutyric acid (IBA) and solidified with 0.6% agar were stored at three different temperatures in the dark for up to 24 weeks. All shoots remained viable for 24 weeks when stored at 3 °C, while at 14 °C the percentage of survival decreased quickly after 12 weeks of storage. At 7 °C, percentage of survival started to decline after 18 weeks of storage. Shoots stored at 3 °C had the highest regeneration rates and shoot lengths following transfer to standard proliferation conditions. This temperature also had a beneficial effect on shoot proliferation during the first 12 to 18 weeks of the experiment.

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Xabier Barandiaran, Nieves Martín, María Fernanda Rodríguez-Conde, Antonio Di Pietro and Jesus Martín

The influence of different callus induction media on the regeneration process in garlic was tested. The auxin 2,4 dichlorophenoxyacetic acid frequently used in garlic tissue culture was found to be detrimental when used at the levels described in the literature. However, combinations of growth regulators commonly used for dicot tissue culture produced high levels of callus induction and regeneration that could be used efficiently in a transformation program.

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James R. Ault and Kayri Havens

Shoot explants from actively growing, greenhouse-maintained plants of Baptisia `Purple Smoke' were cultured in vitro for shoot initiation on Murashige and Skoog (MS) basal medium containing vitamins and supplemented with 30 g·L–1 sucrose, 8.87 μm BA, and 4.14 μm K-IBA. All subsequent media were supplemented with 2.47 mm NaH2PO4 to enhance shoot growth. Single-node explants were subcultured for shoot multiplication on MS medium with either no plant growth regulator or with 2.22, 4.44, 8.87, 17.74, or 35.48 mm BA in combination with 0.0 or 4.14 μm K-IBA. Explants produced a maximum of 4.1 shoots on the medium with 2.22 μm BA. Shoots rooted on all concentrations of K-IBA (2.07, 4.14, 10.36, or 20.72 μm) and K-NAA (2.23, 4.46, 11.15, or 22.29 μm) tested. Maximum rooting was 100% on MS medium with 11.15 μm K-NAA; however, this treatment induced copious stem callusing. Rooted shoots were greenhouse-acclimatized for 2.5 weeks. Overall survival was 86%. For optimal rooting and subsequent acclimatization, treatment with 2.23 μm K-NAA is recommended; this resulted in 83% rooting and 87% acclimatization. Chemical names used: N 6 benzyladenine (BA); potassium salt of indole-3-butyric acid (K-IBA); potassium salt of 1-naphthalene acetic acid (K-NAA).

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Duane W. Greene

Thidiazuron (THI) applied at full bloom (FB) at 10 or 50 mg·liter–1 thinned `McIntosh' apples (Malus domestica Borkh.) and reduced return bloom. The same concentrations applied at 22 days after FB (DAFB) thinned excessively and inhibited return bloom even more. THI at 1, 5, or 15 mg·liter–1 did not thin `Empire' at FB, but when applied 18 DAFB, these concentrations achieved thinning, with 5 mg·liter–1 reducing crop load to near ideal commercial levels. Return bloom of `Empire' was not influenced by THI at these concentrations. THI increased fruit weight, flesh firmness, soluble solids concentration, and fruit asymmetry on `McIntosh' and `Empire' and reduced red pigmentation and seed count on `McIntosh', especially when applied 22 DAFB. A FB application of CPPU and THI, each at 5 or 10 mg·liter–1, on `Delicious' increased the fruit length: diameter (L: D) ratio and flesh firmness (at harvest and following 26 weeks of refrigerated storage and reduced return bloom). CPPU at either 5 or 10 mg·liter–1 increased the fruit L: D ratio more than 25 mg Promalin/liter. Chemical names used: N-phenyl-N′-1,2,3-thiadiazol-5-ylurea (thidiazuron); N-(2-chloro-4-pyridyl)-N′-phenylurea (CPPU); N-(phenylmethyl)-1H-purine-6-amine plus gibberellins A4+7 (Promalin).