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David B. Headley, Nina Bassuk, and Robert G. Mower

Two experiments were conducted to determine the relative resistance of 33 selected cultivars of English ivy (Hedera helix L.) to soil- and shoot-applied NaCl. In the soil-applied NaCl experiment, ramets of the 33 cultivars were irrigated with a fertilizer + 0.25-N NaCl solution for 55 days. `Harrison', `Hibernica', `Thorndale', Wilson', and Woerner' exhibited the least amount of visible shoot damage. Dry weights of all cultivars were much lower in the salt treatment. In the shoot-applied NaCl experiment, plants were sprayed daily with a 0.25-n NaCl solution for 48 days. The young leaves and stems of all cultivars were severely injured by the salt spray, while the mature leaves and stems and the dormant buds were only slightly injured. Reduction in dry weight varied between cultivars. Two subsequent experiments focused on resistance to soil-applied NaCl. Ramets of the NaCl-resistant `Harrison', `Hibernica', and `Thorndale', and the NaCl-sensitive `Baltica', `Cathedral Wall', and Wingertsberg' were irrigated with a fertilizer + 0.25-N NaCl solution for 48 days. Whole-plant Cl content for all six cultivars was in the range of 30,000 ppm. Ramets of `Thorndale' and `Cathedral Wall' were irrigated with a fertilizer + 0.25-N NaCl solution for 30 days with replicate plants harvested at S-day intervals. `Cathedral Wall' accumulated more Cl at a faster rate than `Thorndale'. Mean whole-plant Cl concentration peaked at 97,000 ppm for `Cathedral Wall' and 40,000 ppm for `Thorndale'. Salt resistance may be partly based on slower uptake of Cl.

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Guy Auderset, Charles Moncousin, Jane O'Rourke, and D. James Morré

Root formation in shoot cuttings of soybean (Glycine max L. `Williams'), mungbean (Phaseolus aureas Mdlbg.), English ivy (Hedera helix L.), and apple (Malus ×domestica Borkh. `Jork 9') was stimulated by dithiothreitol and reduced glutathione in the presence and absence of auxin (IAA) shock. In soybean, in the absence of auxin, root formation was stimulated to about the same extent by glutathione alone as with auxin alone. The roots induced by thiol compounds were longer than roots induced by auxin shock and were completely normal in appearance. Roots produced with auxin shock alone were short and exhibited characteristic auxin-induced deformations. With a combination treatment of auxin shock and thiol compounds, roots were more numerous than with either alone, somewhat longer than with auxin alone, and exhibited fewer of the usual deformations characteristic of roots grown in the presence of external auxins. The thiol compounds also were beneficial for rooting Malus shoots propagated from callus in vitro. The thiol compounds were most beneficial with older cuttings where auxin shock was often insufficient to obtain roots. In shoots where rooting was stimulated by thiol agents, shoots grew more rapidly than in those where rooting was induced by auxin shock alone. These findings suggest a use for thiol compounds alone or in combination with auxin shock to induce differentiation of root primordia as well as for stimulation of root growth. Chemical name used: indole-3-acetic acid (IAA).

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Robert L. Geneve, Wesley P. Hackett, and Bert T. Swanson

Exogenous ethylene could not substitute for NAA to induce adventitious root initiation in juvenile petiole explants of English ivy (Hedera helix L.), indicating that the action of auxin-stimulated root initiation was not directly mediated through ethylene production. Mature petioles did not initiate roots under any auxin or ethylene treatment combination. Ethephon or ACC supplied at 50 or 100 μm was inhibitory to NAA-induced root initiation in juvenile petioles. The pattern of ethylene production stimulated by NAA application was significantly different in juvenile and mature petioles. Ethylene evolution by juvenile petioles declined to near control levels during from 6 to 12 days after NAA application. Reduction in ethylene production was due to reduced availability of ACC in juvenile petioles. Mature petioles continued to produce ethylene at elevated levels throughout the course of the experiment. Ethylene does not appear to play a significant role in the differential root initiation response of juvenile and mature petioles treated with NAA. However, ethylene appeared to have an inhibitory effect during root elongation stages of adventitious root development in juvenile petioles. Chemical names used: 1-aminocyclopropane-1-carboxylic acid (ACC); 1-napthaleneacetic acid (NAA); 2-chloroethylphosphonic acid (ethephon).

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Robert L. Geneve, Wesley P. Hackett, and Bert T. Swanson

Several inhibitors of ethylene biosynthesis and action, as well as an atmospheric ethylene scrubber, were used to investigate the role of ethylene in adventitious root initiation in de-bladed petioles from the juvenile and mature phase of English ivy (Hedera helix L.). Induction of root primordia required NAA regardless of the inhibitor treatment. Difficult-to-root mature petioles have been shown to produce higher amounts of ethylene than easy-to-root juvenile petioles. However, mature petioles failed to root under any combination of NAA and inhibitor treatment, indicating that the continued evolution of ethylene in NAA-treated mature petioles was not responsible for the absence of a rooting response. Root initiation in juvenile petioles was not affected by treatment with the ethylene action inhibitors STS and NDE, nor by removal of atmospheric ethylene with KMnO. Inhibition of ethylene biosynthesis using AVG or AOA reduced root initiation in juvenile petioles, but this response was not well-correlated to the observed reduction in ethylene evolution. The inhibitory action of AVG could not be reversed by the addition of ethylene gas or ACC, which indicated that AVG could be acting through a mechanism other than the inhibition of ethylene biosynthesis. Chemical names used: 1-naphthalene acetic acid (NAA); l-aminocyclopropane-l-carboxylic acid (ACC); silver thiosulfate (STS); 2,5-norbornadiene (NDE); aminoethyoxyvinyl-glycine (AVG); aminooxyacetic acid (AOA).

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Dong Sik Yang, Svoboda V. Pennisi, Ki-Cheol Son, and Stanley J. Kays

sequence: ( A ) Hemigraphis alternata , Tradescantia pallida , Hedera helix , Fittonia argyroneura , Asparagus densiflorus , and Hoya carnosa ; ( B ) H. alternata , T. pallida , H. helix , A. densiflorus , H. carnosa , and F. argyroneura ; ( C

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Andrew J. Macnish, Ria T. Leonard, and Terril A. Nell

Asplenium nidus, Chamaedorea elegans ‘Neathe Bella’, Hedera helix ‘Chicago’, and Syngonium podophyllum ‘White Butterfly’. Typically, ethylene responses were very consistent for most genotypes harvested and treated at different times during the growing

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E. Jay Holcomb, Silvia Gamez, David Beattie, and George C. Elliott

Ebb-and-flow irrigation reduced water and fertilizer use by ≈ 40% when compared to overhead hand-watering by hose in the production of Hedera helix. In contrast, water and fertilizer use were not significantly different between ebb-and-flow and drip irrigation systems in the production of Asiatic hybrid lilies. Adequate growth of Hedera helix `Baltica' was obtained with 50 mg N/liter of 20-10-20 (20N-4.4-16.6K) or 20-19-18 (20N-8.4P-14.9K). Also, good market-quality hybrid lilies were produced with 75 mg N/liter of 20-19-18 (20N-8.4P-14.9K), 16-4-12 (16N-1.8P-10K), 20-0-20 (20N-0P-16.6K), and 20-10-20 (20N-4.4P-16.6K).

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Martin F. Quigley

Six durable but slow-to-establish groundcover species, and three fast-growing but short-lived groundcover species, were planted singly and in paired combinations under mature landscape trees to test for relative weed suppression. Installations were replicated on an urban site and a rural site, monitored for two growing seasons, and weeded periodically by hand. All weeds were dried and weighed, and subplot averages (160 observations) for each plant combination were tested by analysis of variance. Weeds were significantly fewer and smaller in the mixed species than in single species subplots. Weed biomass was also significantly less in monospecific groundcover subplots than in unplanted control plots. These results suggest that reduced maintenance cost (and input) for weed control, along with better initial coverage appeal of the paired plantings, may increase marketability of perennial groundcovers.

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Dennis R. Pittenger, David A. Shaw, Donald R. Hodel, and William E. Richie

The performance of six landscape groundcover species was evaluated when irrigated at 30% of ET0 at irrigation schedules of three times per week, once per week, once every 2 weeks, and once every 4 weeks. Potentilla tabernaemontani could not be sustained under any of the treatments. For the other species (Baccharis pilularis, Drosanthemum hispidum, Vinca major, Osteospermum fruticosum, and Hedera helix) there were no season-long differences in a species' performance or density due to irrigation frequency, but there were significant differences among species across irrigation treatments. Drosanthemum and Osteospermum provided good overall appearance and density consistently through the season. Baccharis maintained acceptable performance most of the irrigation season, while Vinca and Hedera became unacceptable in appearance in mid-season. Soil moisture content differed among species, but was not consistently different between irrigation treatments.