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Chuanjiu He, Fred Davies*, Ronald Lacey, and Que Ngo

Elevated levels of ethylene occur in enclosed crop production systems and in space-flight environments—leading to adverse plant growth and sterility. There are engineering advantages in growing plants at hypobaric (reduced atmospheric pressure) conditions in biomass production for extraterrestrial base or spaceflight environments. Objectives of this research were to characterize the influence of hypobaria on gas exchange and ethylene evolution of lettuce (Lactuca sativa L. cv. Buttercrunch). Lettuce was grown under variable total gas pressures [50 and 101 kPa (ambient)]. The six chambered, modular low plant growth (LPPG) system has a Rosemount industrial process gas chromatograph (GC) for determining gas concentrations of oxygen (O2), carbon dioxide (CO2) and nitrogen (N). With the LPPG system, changes in CO2 can be tracked during the light and dark periods on a whole canopy basis, and transpirate collected as a measurement of transpiration. During short growth periods of up to seven days, growth was comparable between low and ambient pressure. However, there was a tendency for leaf tip burn under ambient pressure, in part because of higher ethylene levels. Tip burn increased under high light (600 vs. 300 μmol·m-1·s-1) and high CO2 (600 vs. 100 Pa). The CO2 assimilation rate and dark respiration tended to be higher under ambient conditions. High humidity (100%) reduced CO2 assimilation rate compared to 70% RH. Ethylene was increased by high light (600 vs. 300 μmol·m-1·s-1) and high CO2 (600 vs. 100 Pa). Ethylene was higher under ambient than low pressure. Enhanced plant growth under low pressure may be attributed to reduced ethylene production and decreased dark respiration (lower night consumption of metabolites).

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Chuanjiu He, Fred T. Davies, Ronald E. Lacey, and Sheetal Rao

There are engineering and payload advantages in growing plants under hypobaric (reduced atmospheric pressure) conditions in biomass production for extraterrestrial base or spaceflight environments. Objectives of this research were to characterize the influence of hypobaria on growth, gas exchange, and ethylene evolution of lettuce (Lactuca sativa L. cv. Buttercrunch). Elevated levels of the plant hormone, ethylene, occur in enclosed crop production systems and in space-flight environments—leading to adverse plant growth and sterility. Lettuce plants were grown under variable total gas pressures [25 (low) or 101 kPa (ambient)]. During short growth periods of up to 10 days, growth was comparable between low and ambient pressure plants. Regardless of total pressure, plant growth was reduced at 6 kPa pO2 compared to 12 and 21 kPa pO2. At 6 kPa pO2 there was greater growth reduction and stress with ambient (101 kPa) than low (25kPa) pressure plants. Plants at 25/12 kPa pO2 had comparable CO2 assimilation and a 25% lower dark-period respiration than 101/21 kPa pO2 (ambient) plants. Greater efficiency of CO2 assimilation/dark-period respiration occurred with low pressure plants at 6 kPa pO2. Low pressure plants had a reduced CO2 saturation point (100 Pa CO2) compared with ambient (150 Pa CO2). Low pO2 lowered CO2 compensation points for both 25 and 101 kPa plants, i.e., likely due to reduced O2 competing with CO2 for Rubisco. Ethylene was 70% less under low than ambient pressure. High ethylene decreased CO2 assimilation rate of 101/12 kPa O2 plants. The higher dark-period respiration rates (higher night consumption of metabolites) of ambient pressure plants could lead to greater growth (biomass production) of low pressure plants during longer crop production cycles.

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Sandra B. Wilson, Robert L. Geneve, and Fred T. Davies

Interactive web-based questions were developed for students to review subject matter learned in an online plant propagation course. Articulate Storyline software was used to build nearly 250 review questions with five different testing styles to ascertain proficiency in subject areas, including the biology of propagation, the propagation environment, seed propagation, vegetative propagation, micropropagation, and cell culture. Questions were arranged to correspond to the supporting textbook chapters in Hartmann and Kester’s Plant propagation: Principles and practices, ninth edition. These are open access and available to instructors and students worldwide. Users received immediate feedback for each question answered correctly or incorrectly. The system remembers where one leaves off, which enables starting and stopping multiple times within a chapter. Means of pre- and posttest responses to nine content knowledge items showed that students perceived a significant content knowledge gain in the course. These online interactive reviews can be adapted easily to other courses in a variety of fields, including horticulture, botany, systematics, and biology. They can also be expanded to overlay multiple objects and trigger events based on user response. Since inception, the website hosting these online reviews averaged 156 unique visitors per month. Students have reported this to be a useful tool to prepare them for course exams.

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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.

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Fred T. Davies Jr., Constantino M. Calderón, and Zosimo Huaman

The influence of arbuscular mycorrhizal fungi (AMF) [two Peruvian mixed isolates, a pure isolate of Glomus intraradices] and the flavonoid, formononetin, were tested on growth, yield, and leaf elemental concentration of the Peruvian potato (Solanum tuberosum L.) `Yungay'. Plants started from tissue culture-produced prenuclear minitubers of `Yungay' were subjected to seven treatments, which included noncolonized (non-AMF) plants fertilized with Long Ashton nutrient solution modified to supply P at 11 and 44 μg·mL-1. All AMF plants received low P (11 μg·mL-1) and were inoculated with either a sierra-maize mixed isolate, sierra-papa mixed isolate, pure isolate of G. intraradices, sierra-maize mixed isolate + formononetin, or a sierra-papa mixed isolate + formononetin. Plants were grown in 3-L containers under shade house conditions in Lima, Peru. Non-AMF plants at low P had the poorest growth, while high P plants had the greatest overall growth. All AMF plants had greater growth, including a higher root to shoot ratio, higher phosphorus use efficiency [(g tuber)/(g P/kg tissue)], and a lower leaf to tuber ratio (indicating greater leaf efficiency in producing tuber dry matter), compared to non-AMF plants at low P. The mycorrhizal inoculation effect (MIE) ranged from +44% to +57%, indicating that `Yungay' was moderately to highly mycorrhizal dependent. Plants colonized with the sierra-papa isolate + formononetin had the same tuber development and leaf to tuber ratio, compared to high P, non-AMF plants. Formononetin increased extraradical hyphae formation. Mycorrhizal enhancement was in part due to greater P, Fe, and Mg uptake, a higher phosphorus-use efficiency and greater extraradical hyphae formation.

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Andrès A. Estrada-Luna and Fred T. Davies Jr.

Micropropagated cactus pear plantlets (Opuntia amyclaea Tenore) cv. Reyna were colonized with a Mexican endomycorrhiza isolate, ZAC-19 (containing Glomus etunicatum and two unknown Glomus spp.) and fertilized with two phosphorous levels (0 and 11 μg P/ml) to study their effect on plant growth and nutrient uptake. After 7 months of greenhouse culture, there was 100% survival of the micropropagated cactus pear plants. Evidence of mycorrhizal colonization was observed 5 days after inoculation, with the development of internal hyphae in root cortices. At the end of the study, high colonization occurred (48% to 54%) with no differences in P treatments. Plantlets transferred to soil began to actively grow with no lag phase. However, plant growth rate was significantly affected by treatments. Absence of P supply and lack of colonization resulted in lower dry mass and surface area of prickly pear cactus plants. In contrast, the combination of supplementary P and mycorrhizal colonization significantly increased plant growth.