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Mariateresa Cardarelli, Youssef Rouphael, Francesco Saccardo and Giuseppe Colla

A research project was conducted at the University of Tuscia, Viterbo (central Italy), to set up a vegetative propagation system for producing diseasefree artichoke transplants (Cynara cardunculus var. scolymus) of the Romanesco type (cultivar C3). The system included the following steps: 1) micropropagated plantlets were grown in a soilless culture year-round in greenhouse conditions, starting at the end of August; 2) stock plants were periodically treated with a chemical growth regulator [6-benzylamino purine (BA)] and then cut back at the collar level to promote offshoot production; 3) offshoots were periodically harvested and cold stored; and 4) cuttings were rooted at the end of spring under conditions of high humidity in multi-pack trays so as to be ready for summer transplanting. Results showed that the foliar application of BA to the stock plants increased the offshoot number quadratically to 200 mg·L-1. The rooting percentages of cuttings and root growth were enhanced by raising the cutting weight class (30-45 g) and by the application of naphthaleneacetic acid (NAA) to the cutting root zone at a rate of 2000 mg·L-1. The percent rotten cuttings increased as the 2 °C cold-storage time increased from 30 to 150 days. Similarly, the percentage of rooting and root growth decreased approximately from 60 to 150 days.

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Sarah E. Bruce, D. Bradley Rowe and James A. Flore

Chlorophyll fluorescence over the course of stem cutting propagation was examined in 10 cultivars of Taxus ×media (Taxus baccata L. × T. cuspidata Sieb. & Zucc.), including `Brownii', `Dark Green Pyramidalis', `Dark Green Spreader', `Densiformis', `Densiformis Gem', `Hicksii', `L.C. Bobbink', `Runyan', `Tauntoni', and `Wardii'. The fluorescence value measured was the ratio of variable over maximum chlorophyll fluorescence (Fv/Fm). This value reflects the maximum dark-adapted photochemical efficiency of photosystem II (PSII) reaction centers involved in photosynthesis and is an indirect measure of plant stress. The objective of this study was to examine Fv/Fm as a method for stock plant selection and for monitoring rooting progress of various cultivars. Fv/Fm varied significantly (P ≤ 0.05) among cultivars, initially and over time. However, there was significant overlap among some cultivars. The Fv/Fm decreased dramatically during cold storage, but usually returned to original levels after several weeks in the propagation beds. This appeared to be a reflection of the reduction of water stress as the cuttings formed roots. Initial stock plant Fv/Fm was not correlated (P ≤ 0.05) with rooting percentage, root number, root dry weight, or root length, indicating that Fv/Fm is not a reliable indicator of stock plant rooting potential. Visual assessment is just as reliable.

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J. Ben-Jaacov, A. Ackerman, E. Tal and G. Jacobs

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Paul H. Henry, Frank A. Blazich and L. Eric Hinesley

Studies were conducted to investigate the effects of season (timing), IBA application, genotype, crown position, type of cutting (straight vs. heel), cutting length, and stock plant age upon adventitious rooting of stem cuttings of eastern redcedar (Juniperus virginiana L.). Genotype had a strong influence on percent rooting, root count, and root length of 4-year-old trees. With trees of this age, percent rooting was maximized (87%) with hardwood cuttings taken in January and treated with 5000 ppm IBA. Crown position from which cuttings were collected did not influence rooting. Straight cuttings, with or without a light wound, rooted at a significantly higher percentage (78%) than heel cuttings (52%). With 30-year-old trees, cuttings from the lower third of the crown rooted at a significantly higher percentage (67%) than cuttings from the middle third (43%). Better rooting was obtained with straight (68%) than heel (47%) cuttings. Cutting length affected rooting, with root count and length highest in longer cuttings. Increased tree age reduced rooting, although cuttings from 40-year-old trees retained substantial rooting capacity. Chemical name used: 1 H-indole-3-butyric acid (IBA).

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Phillip A. Wadl, Timothy A. Rinehart, Adam J. Dattilo, Mark Pistrang, Lisa M. Vito, Ryan Milstead and Robert N. Trigiano

refine the standard seed germination protocol, in vitro seed germination methodology, and vegetative propagation techniques, including in vitro multiplication of cloned plantlets, to facilitate ex situ conservation and development of a new methodology for

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Susan Foster and S.L. Kitto

Spigelia marilandica, an herbaceous perennial native to the temperate eastern United States, has great potential for the sunny garden; however, its availability is limited due to propagation difficulties. The effect of stock plant environmnet on the rooting capability of the cuttings is the primary focus of this research. Shoot-tip cuttings were collected monthly from stock plants maintained under high-intensity sodium lamps providing a 16 hr day/8 hr night photoperiod. Cutting bases were dipped in Hormodin I (1000 IBA), placed in a perlite:peat (4:1) mix, and placed under mist for 8 weeks. Preliminary data indicates that 95.5% of the cuttings rooted with an average of 39 roots per cutting.

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Sarah E. Bruce and D. Bradley Rowe

Propagation failures of Taxus are often attributed to cutting collection from stock plants of poor quality. If a quick, reliable method of determining the potential rooting of cuttings based on the condition of a specific stock plant was available for propagators, rooting success could be predicted before investing time, labor, and resources. Our studies examined chlorophyll fluorescence (Fv/Fm) as a potential tool for stock plant selection, assessment of storage conditions, and measurement of stress over the course of propagation. Ten cultivars of Taxus × media (Taxus baccata L. × T. cuspidata Sieb. & Zucc.) were used: Brownii, Dark Green Pyramidalis, Dark Green Spreader, Densiformis, Densiformis Gem, Hicksii, L.C. Bobbink, Runyan, Tauntoni, and Wardii. Storage condition treatments consisted of desiccation (low, medium, and high), duration (34, 70, and 107 days), and temperature (–30, –2.5, 0, 2.5, 5, 10, and 20 °C). Cultivars differed in Fv/Fm initially as well as over time. Correlations were not found between initial stock plant Fv/Fm and rooting percentage, number of roots, root dry weight, or root length, indicating that Fv/Fm is not a reliable indicator of stock plant propagation potential. Short storage duration at –2.5 to 2.5 °C was found to be ideal. Fv/Fm could detect substandard storage conditions only at temperature and desiccation extremes. Although chlorophyll fluorescence measurements do not appear to be a practical method of predicting adventitious rooting, there is a potential for assessing cutting or plant quality before shipping.

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Susan Foster and S.L. Kitto

Wild populations of Spigelia marilandica, a clump-forming perennial, are being destroyed because of its recent popularity and the plant is now becoming rare in its native habitat. The effect of the stock plant environment on the rooting capability of Spigelia marilandica cuttings is the primary focus of this research. Cuttings were obtained from greenhouse (GH) grown plants on a monthly basis, and from plants maintained in outside field beds (FB), season permitting. Cuttings were dipped in Hormodin 1 (1000 IBA), placed in a perlite:peat mix, and put under mist for 8 weeks. During the experiment, 91% rooting of cuttings obtained from GH-grown plants and 35% rooting of cuttings obtained from FB-maintained plants was observed. Cuttings from GH-grown plants averaging 39 roots/cutting (average FW/cutting = 1.243 g, average DW/cutting = 0.1574 g) were compared to cuttings obtained from FB-maintained plants averaging 9 roots/cutting (average FW/cutting = 0.6041 g, average DW/cutting = 0.0663 g). A statistically significant difference was found between the two stock plant environments, with the cuttings from the GH-grown plants having an advantage over the cuttings obtained from the FB-maintained plants. A separate comparison was made of the cuttings obtained from the GH-grown plants over the 12 months of the experiment and the analysis showed no significant difference in the average FW/cutting, DW/cutting, and the number of roots/cutting.

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Jimmy L. Tipton

Effect of cutting age (weeks after budbreak) and K-IBA concentration on percent rooting of Mexican redbud [Cercis canadensis var. mexicana (Rose) M. Hopkins], larchleaf goldenweed [Ericameria laricifolia (Gray) Shinners], littleleaf ash (Fraxinus greggii Gray), and evergreen sumac (Rhus virens Gray) were investigated. For cuttings treated with K-IBA, maximum predicted percent rooting from regression analysis was 88% for cuttings of Mexican redbud taken 4 weeks after budbreak and treated with 21 g·liter-1, 99% for larchleaf goldenweed taken 6 weeks after budbreak and treated with 16 g·liter-1, 86%, for littleleaf ash taken 16 weeks after budbreak and treated with 17 g·liter-1, and 24% for cuttings of evergreen sumac taken 16 weeks after budbreak and treated With 5 g·liter-1. Chemical names used: potassium salt of 1H-indole-3-butanoic acid (K-IBA).