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Paula M. Pijut and Melanie J. Moore

Juglans cinerea L. (butternut) is a hardwood species valued for its wood and edible nuts. Information on the vegetative propagation of this species is currently unavailable. Our objective was to determine the conditions necessary for successful stem-cutting propagation of butternut. In 1999 and 2000, 10 trees (each year) were randomly selected from a 5- and 6-year-old butternut plantation located in Rosemount, Minn. Hardwood stem cuttings were collected in March, April, and May. Softwood cuttings were collected in June and July. K-IBA at 0, 29, or 62 mm in water and IBA at 0, 34, or 74 mm in 70% ethanol were tested for root induction on cuttings. The basal end of cuttings were dipped in a treatment solution for 10 to 15 seconds, potted in a peat: perlite mixture, and placed in a mist bed for 5 to 8 weeks. Rooted cuttings were gradually hardened off from the mist bed, allowed to initiate new growth, over-wintered in a controlled cold-storage environment, and then outplanted to the field. For hardwood cuttings, rooting was greatest for those taken in mid-May (branches flushed out), 22% with 62 mm K-IBA and 28% with 74 mm IBA. Softwood cuttings rooted best when taken in June (current season's first flush of new growth or softwood growth 40 cm or greater) and treated with 62 mm K-IBA (77%) or 74 mm IBA (88%). For 1999, 31 out of 51 rooted softwood cuttings (60.8%) survived overwintering in cold storage and acclimatization to the field. For 2000, 173 out of 186 rooted softwood cuttings (93%) survived overwintering and acclimatization to the field. Chemical names used: indole-3-butyric acid-potassium salt (K-IBA); indole-3-butyric acid (IBA).

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Michael A. Arnold and Eric Young

After receiving 0, 600, 1200, or 1800 hr. of chilling at 5C, one-year-old Malus domestica Borkh. seedlings were given 10 sec. root dips either 10,000 ppm K-IBA solution or water control. Following chilling and IBA treatments, 20 seedlings of each combination were placed in forcing conditions of 20 ± 2C root temperatures and either 20 or 5 ± 1C shoot temperatures. Five seedlings of each treatment were harvested after 0, 7, 14, and 21 days of forcing. Five C prohibited budbreak and bark slipage for up to 21 days. Under 20C, budbreak, shoot elongation and root growth all occurred earlier, faster, and reached a higher level with increased chilling. Twenty C root and 5C shoot temperatures during forcing resulted in large increases in the growth of adventitious shoots on lateral roots, but had little effect on the formation of adventitious shoots on the tap root. K-IBA prohibited development of adventitious shoots on roots, reduced shoot elongation more so than budbreak, and increased root regeneration across chilling hours. K-IBA inhibition of adventitious shoots did not alter the overall pattern of root regeneration enhancement by chilling.

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Michael A. Arnold and Eric Young

After receiving 0, 600, 1200, or 1800 hr. of chilling at 5C, one-year-old Malus domestica Borkh. seedlings were given 10 sec. root dips either 10,000 ppm K-IBA solution or water control. Following chilling and IBA treatments, 20 seedlings of each combination were placed in forcing conditions of 20 ± 2C root temperatures and either 20 or 5 ± 1C shoot temperatures. Five seedlings of each treatment were harvested after 0, 7, 14, and 21 days of forcing. Five C prohibited budbreak and bark slipage for up to 21 days. Under 20C, budbreak, shoot elongation and root growth all occurred earlier, faster, and reached a higher level with increased chilling. Twenty C root and 5C shoot temperatures during forcing resulted in large increases in the growth of adventitious shoots on lateral roots, but had little effect on the formation of adventitious shoots on the tap root. K-IBA prohibited development of adventitious shoots on roots, reduced shoot elongation more so than budbreak, and increased root regeneration across chilling hours. K-IBA inhibition of adventitious shoots did not alter the overall pattern of root regeneration enhancement by chilling.

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Carlos A. Lazcano, Fred T. Davies Jr., Sharon A. Duray, Andres Estrada-Luna, and Victor Olalde-Portugal

Mature cladodes of prickly-pear cactus (Opuntia amyclaea Tenore. cv. Reina) were treated with five wounding methods and four concentrations of potassium salt indolebutyric acid (K-IBA) to stimulate adventitious root formation. K-IBA from 4144 to 41,442 μm (1000 to 10,000 mg·L-1) increased root number and root dry weight; however, root length was decreased at 41,442 μm (10,000 mg·L-1). Root number and root dry weight were higher with wounding methods that had larger wounded surface areas. K-IBA altered rooting polarity and stimulated adventitious root formation along the wounded cladode surfaces. Treatments without suberization had a higher percentage of rotted cladodes. This research validates the commercial practice in Mexico of suberizing cladodes early in the propagation cycle. Auxin application could be of commercial benefit for enhanced rooting in the clonal regeneration of new selections for prickly-pear cactus orchards. The wounding methods and auxin treatments utilized make an excellent classroom demonstration for manipulating rooting polarity.

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James R. Ault

Optimal axillary shoot proliferation was obtained from stem explants of a clone of Eriostemon myoporoides DC. on Murashige and Skoog (MS) basal medium containing 0.1 mg BA/liter, and of Eriostemon `Stardust' on MS medium containing 0.5 mg BA/liter. Overall average number of shoots and shoot lengths for all treatments was greater for E. `Stardust' (22.4 shoots and 12.1-mm shoot length) than for E. myoporoides (4.5 shoots and 8.3-mm shoot length). Maximum percent rooting of E. myoporoides (42%) and E. `Stardust' (95%) was obtained on MS medium supplemented with 1.0 mg K-IBA/liter for E. myoporoides and 0.1 mg NAA/liter for E. `Stardust'. Overall average percent rooting and root lengths were greater for E. `Stardust' (42% rooting and 11.0-mm root length) than for E. myoporoides (27% rooting and 2.3-mm root length). For E. `Stardust', reducing sucrose in the rooting medium from 50 to 25 g·liter-1 significantly decreased overall average percent rooting to 1670 and root length to 6.8 mm. Plantlets of both clones were acclimatized in the greenhouse and transferred successfully to soil, although survival was <7070. Chemical names used: N -(phenylmethyl) -l H -purine-6-amine (BA); potassium-l H -indole-3-butyric acid (K-IBA); l-naphthaleneacetic acid (NAA).

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James R. Ault

Shoot initiation and multiplication were obtained in vitro from immature flower bud and leaf explants of Veltheimia bracteata Bak. `Lemon Flame' and from leaf explants of V. bracteata `Rosalba' cultured on a Murashige and Skoog (MS) medium supplemented with sucrose at 30 g•L–1, and either 8.87 μm BA plus 0.54 μm NAA or 8.87 μm BA plus 5.40 μm NAA. Shoot initiation and multiplication was obtained from a single leaf explant of Veltheimia capensis (L.) DC. on MS medium with 8.87 μm BA plus 0.54 μm NAA. Shoots of the three genotypes rooted on subculture to medium with 0.0, 4.14, or 8.29 μm K-IBA or 0.0, 4.46, or 8.92 μm K-NAA. Maximal rooting was 98% for V. bracteata `Lemon Flame', 95% for V. bracteata `Rosalba', and 98% for V. capensis, from medium with 4.46 μm KNAA. Rooted shoots were acclimatized for 3 to 4 weeks. Overall survival percentage was 69% for V. bracteata `Lemon Flame', 65% for V. bracteata `Rosalba', and 83% for V. capensis. Chemical names used: 6-benzyladenine (BA); potassium salt of indole-3-butyric acid (K-IBA); potassium salt of 1-naphthaleneacetic acid (K-NAA); 1-naphthaleneacetic acid (NAA).

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C.C. Montgomery, B.K. Behe, D.J. Eakes, T.S. Krentz, and V.V. Allen

Buddleia, or butterfly bush, is a popular landscape plant because it attracts wildlife and has some heat and drought tolerance. Dirr and Heuser reported that softwood cuttings of most cultivars rooted well with a basal treatment of 3000 ppm IBA. A rooting study of 11 Buddleia cultivars was conducted in Sept. 1993 and was repeated in May 1994. Terminal softwood cuttings were treated with a quick dip of 0, 1500, 3000, 6000 ppm K-IBA. Generally, increasing rates of IBA increased root count and decreased root length. Root dry weight was minimally affected. `Royal Red', `Empire Blue', and `Lochinch' had 94% to 95% rooted cuttings. Other cultivars rooted equally better. Most cultivars produced shorter, more numerous roots in spring when a higher IBA concentration was used.

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Charlotte R. Chan and Robert D. Marquard

Hamamelis cultivars are typically propagated by grafting onto H. virginiana rootstock. Grafting is labor-intensive and the understock frequently suckers which can lead to the loss of the scion. A cultivar growing on its own root system would eliminate this problem. Our research was undertaken to develop a successful method of rooting micropropagules. The source material was established cultures of H. × intermedia `Diane,' H. virginiana, and a H. vernalis selection. The rooting treatments consisted of four concentrations of K-IBA (0, 5, 10, and 20 μM) in 0.02% Tween 80. Three replicates of eight cuttings each were taken from the three sources for each of the four treatments. The cuttings were placed in 50-mL beakers, cut-end down, with 10 mL of the treatment solution. The beakers were sealed with Parafilm, and cuttings were soaked for 24 h. After treatment, the cuttings were randomly stuck into Kadon flats prepared in advance with a sterile mix of 1 peat: 1 perlite and were watered-in. Cuttings were misted, and flats were covered with plastic and Remay. They were kept in a warm (19-24 °C) greenhouse. Cuttings rooted in 3 to 4 weeks and were subsequently fertilized weekly with Peter's 20N-20P-20K at 150 ppm. At 12 weeks, data were collected for the rate of survival, height, branching, number of nodes, and root mass, and the plants were transplanted to quart pots. Ninety percent of the cuttings rooted; the most favorable response was with 10 μM K-IBA, although all treatments produced >80% rooting. This method was time and labor efficient. Moreover, micropropagation is not dependent on the season, and production of new plants could proceed on a continuous basis, making this a viable alternative to commercial grafting.

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Carrie E. Green and David R. Hershey

Fundamental research on mineral nutrition of azalea has been restricted due to the lack of a model experimental system for growing azaleas in solution culture. The need to maintain a clean root system dictates that azalea cuttings be rooted in solution. A propagation system (HortScience 24:706) was used to root 10-cm long terminal shoot cuttings of azalea `Delaware Valley White' under intermittent mist in a greenhouse. Cutting bases were dipped in 8,000 mg/liter K-IBA for 40 seconds before rooting. Rooting percentages after 7 weeks were 6, 10, and 50% for rooting solutions of tap water, modified 20% Hoagland solution, and 2mM CaCl2, respectively. After an additional 5 weeks the rooting percentage had increased to 83% in the 2 mM CaCl2 treatment. Three other azalea cultivars were found to root much slower than `Delaware Valley White'. Acclimatization of rooted cuttings to the normal greenhouse environment is essential to prevent leaf necrosis and is accomplished by gradually reducing the misting frequency prior to removal from under intermittent mist.

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Carrie E. Green and David R. Hershey

Fundamental research on mineral nutrition of azalea has been restricted due to the lack of a model experimental system for growing azaleas in solution culture. The need to maintain a clean root system dictates that azalea cuttings be rooted in solution. A propagation system (HortScience 24:706) was used to root 10-cm long terminal shoot cuttings of azalea `Delaware Valley White' under intermittent mist in a greenhouse. Cutting bases were dipped in 8,000 mg/liter K-IBA for 40 seconds before rooting. Rooting percentages after 7 weeks were 6, 10, and 50% for rooting solutions of tap water, modified 20% Hoagland solution, and 2mM CaCl2, respectively. After an additional 5 weeks the rooting percentage had increased to 83% in the 2 mM CaCl2 treatment. Three other azalea cultivars were found to root much slower than `Delaware Valley White'. Acclimatization of rooted cuttings to the normal greenhouse environment is essential to prevent leaf necrosis and is accomplished by gradually reducing the misting frequency prior to removal from under intermittent mist.