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Yong Cheong Koh and Fred T. Davies Jr.

The leaves of vegetative stolons of greenhouse grown Cryptanthus `Marian Oppenheimer' (wide leaf clone) were cultured in modified MS media to induce adventitious shoot formation via callus formation. The best callus induction medium was basal MS medium with 10 μM NAA, IBA and BA. Pure green (843), maroon (3), striped (2) and albino plantlets were obtained. Most of the albino plantlets were stunted, tightly clumped together and impossible to score. The medium which produced the highest average number of non-albino plantlets was basal MS medium with 0.3 μM NAA, IBA and BA All non-albino plantlets were rooted in MS medium with 5.4 μM NAA and transplanted ex vitro with a survival rate of 96.7%. The maroon plantlets became green two weeks after transplanting. Histological studies revealed that C. `Marian Oppenheimer' (wide leaf clone) has two tunicas (L1 and L2) and a corpus (L3). Callus on the leaf explant arose mainly from the L2 and L3. Apparently C. `Marian Oppenheimer' (wide leaf clone) is a GWG periclinal chimera.

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Sharon A. Duray and Fred T. Davies Jr.

Plant propagation instructors are challenged to develop laboratory exercises that demonstrate the theoretical aspects of seed germination. Seed priming or osmoconditioning is a relatively new technigue that has been shown to improve seed performance in horticultural crops. An esaily constructed seed priming system was designed using a pair of 2-liter glass jars, 2 aquarium pumps and air tubing. Eight sets of 40 seeds were each wrapped in coffee filters and laced in aerated treatment solutions consisting of 50 mmole K H2P O4 or an untreated control of distilled water. All seeds were treated or 0, 1, 3 or 5 days. Upon completion, seeds were rinsed, dried and placed into petri dishes containing moist filter paper to observe germination. A good test species for this exercise is Vinca rosea which typically has a poor germination percentage and rate. Seeds primed for 3 and 5 days significantly enhanced both germination percentage and rate in Vinca.

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Lop Phavaphutanon and Fred T. Davies Jr.

Growth and nutrient content of neem tree seedlings (Azadirachta indica A. Juss) were studied in response to the mycorrhial fungi Glomus intraradices Schenck & Smith and Long Ashton Nutrient Solution (LANS) modified to supply phosphorus (P) at 0.65 and 1.30 mM P. Three months after inoculation, an extensive mycorrhizal colonization was observed in mycorrhizal plants at both P levels. Shoot growth of mycorrhizal plants was similar at both P levels while the growth of nonmycorrhizal plants increased with increasing P supply. Mycorrhizal plants had greater leaf area, shoot dry weight and root to shoot ratio than nonmycorrhizal plants at the same P level. The length of nonsuberized roots increased with increasing P supply regardless of mycorrhizal colonization while the length of suberized roots was significantly increased by mycorrhiza. Mycorrhiza altered dry mass partitioning to root systems resulting in greater length and dry weight of suberized roots in mycorrhizal plants. Mycorrhiza also improved nitrogen, phosphorus, calcium and sulfur uptake but did not affect micronutrient uptake, except for enhancing boron.

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Sven E. Svenson and Fred T. Davies Jr.

Variation in tissue elemental concentration in apical stem cuttings of `Lilo' and `V-10 Amy' poinsettia (Euphorbia pulcherrima Willd. ex. Klotzch) were studied during the initiation and development of adventitious roots. Changes in selected macro- and micro-element concentrations coincided with root initiation (i.e., Fe, Cu, and Mo accumulated in the basal portions of stem cuttings during early root initiation before root primordia elongation); P, K, Ca, and Mg concentrations declined. During root primordia elongation and root emergence, Fe, Cu, and Mo and Mg, Mn, B, and Zn concentrations continued to increase at the cutting bases, but P and K concentrations remained low compared to when cuttings were initially inserted in the propagation medium. When all cutting of both cultivars had rooted, foliar N, Fe, and Mo concentrations declined, but Cu increased compared to when cuttings were initially propagated.

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Sharon A. Duray and Fred T. Davies Jr.

A laboratory exercise is outlined and discussed for seed priming, or osmoconditioning. The exercise was developed using an easily constructed and inexpensive seed-priming system. A variety of horticultural seeds can be used to give students experience and exposure to some of the benefits of seed priming. Seed germination data usually can be obtained within 6 to 8 days, depending on the species used. The laboratory may be modified to stress various features of seed priming, including priming agents, optimal concentrations, and ranges of germination temperatures.

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Lucila Amaya Carpio, Fred T. Davies Jr., and Michael A. Arnold

This research determined the effects of two commercial arbuscular mycorrhizal fungi (AMF) inocula, organic slow-release fertilizer (OSRF), and inorganic controlled-release fertilizer (ICRF) on plant growth, marketability and leachate of container-grown Ipomoea carnea N. von Jacquin ssp. fistulosa (K. Von Martinus ex J. Choisy) D. Austin (bush morning glory) grown outdoors under high temperature summer conditions (maximum container media temperature averaged 44.8 °C). Uniform rooted liners were planted into 7.6-L pots containing a pasteurized substrate [pine bark and sand (3:1, by volume)]. The AMF treatment consisted of BioterraPLUS and MycorisePro and a noninoculated control (NonAMF). Fertilizer treatments included OSRF [Nitrell 5-3-4 (5N-1.3P-3.3K)] and ICRF [Osmocote 18-7-10 (18N-3.0P-8.3K)]. OSRF was tested at three rates: 8.3, 11.9, and 16.6 kg·m-3, which were respectively, 70%, 100%, and 140% of manufacturer's recommended rate, while ICRF was tested at two rates: 3.6 and 7.1 kg·m-3, which were, respectively, 50% and 100% of manufacturer's recommended rate. The P levels were equivalent between 70% and 140% OSRF and, respectively, 50% and 100% ICRF. Greatest growth [leaf, shoot, flower bud, and flower number; root, leaf, shoot, and total plant dry mass (DM); growth index; leaf area]; N, P, and K uptake; leaf chlorophyll; and plant marketability occurred with BioterraPLUS plants at 50% and 100% ICRF rate and MycorisePro at the 100% ICRF rate. Greater plant growth occurred with increasing fertility levels; however, plants at the 140% OSRF (same P level as 100% inorganic SRF) had poorest growth, in part due to high temperature. While AMF enhanced growth of plants with OSRF at all concentrations, better growth and marketability occurred with ICRF than OSRF plants inoculated with AMF. AMF plants at the 50% ICRF had comparable or better growth, higher N, P, and K and marketability than NonAMF plants at either 100% OSRF or ICRF. AMF were able to survive under high temperature and colonize plants grown from low to high fertility conditions. AMF inoculation had minimal effect on container leachate (pH and electrical conductivity). However, the larger-sized AMF plants at 100% ICRF rate had greater total leaf tissue N, P, and K, suggesting greater nutrient utilization—thus reduced potential risk for leachate runoff.

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Thomas W. Zimmerman, Fred T. Davies Jr., and Jayne M. Zajicek

Dyssodia pentacheta, a prostrate-growing perennial Texas wildflower with potential for use in low-maintenance landscapes, was propagated in vitro and by stem cuttings under mist. Optimum rooting for IBA-treated semihardwood terminal stem cuttings (3 to 30 mm IBA) and in vitro-grown nodal segments (30 to 100 mm IBA) occurred after 4 weeks under an intermittent mist system. A 300-mm IBA basal dip was lethal to macroand microcuttings. In vitro, D. pentacheta produced more shoots per nodal explant on Woody Plant Medium (2 g Gelrite/liter) with 1 to 10 μ m BA than with combinations of BA and 0.5 μm NAA. After shoot proliferation, the shoots were subculture twice and grown on growth regulator-free medium. When maintaining D. pentacheta in vitro on media devoid of plant growth regulators, 1% sucrose was more effective than 2% for promoting shoot growth and suppressing apparent production of phenolics. Chemical names used: N-(phenylmethyl) -1H-purin-6-amine (BA); 1H-indole-3-butyric acid (IBA); 1-naphthaleneacetic acid (NAA).

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Sven E. Svenson, Fred T. Davies Jr., and Calvin E. Meier

The influence of ectomycorrhizae on drought acclimation was studied in an open-pollinated family of loblolly pine (Pinus taeda L.). Seedlings inoculated with Pisolithus tinctorius (Pers.) Coker and Couch (Pt) maintained a higher shoot relative growth rate under high and low soil moisture regimes. However, fascicle area, shoot and root mass, and fascicle nutrient elemental content were similar for seedlings inoculated with Pt and noninoculated seedlings. Seedlings under low soil moisture were drought-acclimated by five 11-day drought cycles. During peak water deficit (cycle 6), drought-acclimated, Pt-inoculated seedlings had the lowest predawn fascicle water potential (ψ pd), conserved water with lowest bulk fascicle diffusive conductance (g), and maintained low g and transpiration (E) during recovery (cycle 6). Enhanced drought acclimation of Pt-inoculated seedlings was independent of plant size and fascicle nutrient content.

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Jonathan N. Egilia, Fred T. Davies Jr, and Sharon Duray

Hibiscus plants, were irrigated with full strength Hoagland's nutrient solution containing either 0,2,5, or 10 mM potasium(K). After 72 days of K treatment, half of the plants at each K level were subjected to a 21-day slowly developing drought stress cycle and the other half were non-drought stressed (ND). Mid-day leaf water potentials at day 21 was-1.5 to-1.6 MPa (DS), and -0.5 MPa (ND). Leaf K concentration increased with increasing K in nutrient solution for both DS and ND plants, but K was higher in DS than ND plants at 2.5 and 10 mM K. Of the macronutrient cations, only (Ca) was inversely correlated with nutrient solution K, in both DS and ND plants. Leaf concentrations of all the micronutrient cations increased with increasing K supply, regardless of drought stress. Potassium hadt significant positive correlation with total plant and leaf dry weight of DS, but not ND plants. Leaf stable carbon isotope composition (δ13 C,an estimate of long term water-use efficiency), was positively correlated with N, Mg and Ca, and negatively correlated with K, iron (Fe), and K:total cation ratio regardless of drought stress. Both net photosynthesis and stomatal conductance were negatively correlated with N and Ca, but positively correlated with K, Fe and manganese in ND plants.

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Fred T. Davies Jr., Randal S. Stahl, and Sharon A. Duray

Symbiotic mycorrhizal fungi increase the P uptake of agronomic, horticultural, and forestry crops. Little is known about the real-time dynamics of carbon balance (net gain of biomass resulting from photosynthesis less the respiratory costs) of plants colonized with mycorrhizae. Our objective was to determine the carbon balance of endomycorrhizal (VAM) chile pepper `San Luis' (Capsicum annuum L.) as a model system for predicting plant response to limited P availability under elevated CO2. The increase in atmospheric CO2 is expected to result in increased plant productivity and greater demand for soil P, however, the lack of available soil P may become the most important nutritional problem limiting crop productivity. Under current conditions, the limitation of soil-P availability is an enormous problem that affects 25% of the world's arable lands. We are quantifying the carbon costs paid by the mycorrhizal plant under varying levels of P deficiency over the life cycle of the plant. Preliminary results from this study under ambient CO2 conditions indicate that there is a lower maintenance respiration and higher growth efficiency with mycorrhizal pepper plants under low soil-P conditions.