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Steven E. Newman and Jeffrey S. Tant

An experiment was conducted to determine the influence of eight commercial root-zone media (four peat based and four pine bark based) on the effects of paclobutrazol applied to Euphorbia pulcherrima Willd. `Eckespoint Celebrate 2' as an impregnated spike or a drench. Paclobutrazol treatments had the least influence on stem elongation of poinsettias grown in the peat-based medium containing Bacctite, a compressed peat product designed to increase aeration and cation exchange capacity, or composted pine bark ground to a particle size that could pass through an opening 1 cm or smaller. Spikes were more effective at reducing shoot elongation than drenches. Spike treatments also resulted in lower bract dry-matter accumulation than drenches. Paclobutrazol applied as a spike to poinsettias at pinch could combine pinching and chemical growth regulator application into one simultaneous operation. Chemical name used: (±)-(R*,R*)-beta-[(4-chlorophenyl)methyl]-alpha-(1, 1,-dimethyl)-1H-1,2,4,-triazole-1-ethanol (paclobutrazol).

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Michael A. Arnold and Eric Young

CuCO3 at 100 g·liter-1 in a paint carrier applied to interior container surfaces effectively prevented root deformation in container-grown Malus domestica Borkh. and Fraxinus pennsylvanica Marsh. seedlings. CuCO3 treatments nearly doubled the number of white unsuberized root tips in both species. CuCO3 treatment increased some measures of root and shoot growth before and after transplanting to larger untreated containers. Root pruning at transplanting tended to reduce root and shoot fresh and dry matter accumulation in F. pennsylvanica seedlings and shoot extension in M. domestica seedlings. In some cases, root pruning of M. domestics at transplanting from CuCO3-treated containers increased root growth compared to unpruned CuCO3-treated and untreated seedlings. Changes in growth induced by CuCO3 and root pruning were not related to changes in trans -zeatin riboside-like activity in the xylem sap of-apple.

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Donald E. Irving, Paul L. Hurst and Jonathan S. Ragg

During this study, we divided the developmental growth pattern of buttercup squash into three phases: 1) early growth, from flowering up to 30 days after flowering; 2) maturation, from 30 days until 60 days after flowering (or harvest); and 3) ripening, from 60 days (or harvest) until ≈100 days after flowering. Harvest occurred at 48 days after flowering. Fruit growth (expansion), starch, and dry matter accumulation were largely completed during early growth, and there was a progressive decline in the respiration rate. Extractable activities of acid and alkaline invertases, sucrose synthase, alkaline α-galactosidase, and sucrose phosphate synthase (assayed with saturating substrates) were high initially but declined markedly during this phase. Glucose, fructose, and low concentrations of raffinose saccharides were present, but no sucrose was detected. During maturation, starch and dry matter remained nearly constant and sucrose began to accumulate. During ripening, starch was degraded, sucrose synthase activity was significant but relatively constant, sucrose phosphate synthase activity increased, and sucrose continued to accumulate.

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Stephen Reiners and Stephen A. Garrison

The effect of soil moisture levels on the yield and dry matter accumulation of asparagus (Asparagus officinalis L) using the motherstalk method was examined in a greenhouse study. This technique allows for a spear to develop a mature fern while permitting harvest of later-developing spears. The motherstalk treatment resulted in significantly heavier spears as compared to the conventional practice without a motherstalk and harvesting all spears. In addition, crown weights between the motherstalk and the nonharvested treatment were similar at the end of the 12-week harvest period, but significantly lower when spears were harvested without the benefit of a motherstalk. Optimizing soil moisture significantly increased yield in the motherstalk treatment and increased the fern dry weight but had no effect on crown dry weight. Our results indicate that the motherstalk system may allow for extended asparagus harvest in temperate areas but soil moisture may need to be carefully monitored to use this technique.

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Teresa A. Cerny, Nihal C. Rajapakse and Ryu Oi

A research collaboration between Clemson Univ. and Mitsui Chemicals, Japan, has been established to develop and test photoselective greenhouse covers that can filter out far-red (FR) light and control plant height with minimal use of chemicals. The effects of polymethyl methacylate (PMMA) filters containing FR-intercepting dyes were evaluated on watermelon, pepper, chrysanthemum, and tomato to select an optimum dye concentration. As the dye concentration increased, FR interception increased, photosynthetic photon flux (PPF) decreased, and phytochrome photoequilibrium increased from 0.72 to 0.82. Light transmitted through photoselective filters reduced plant height effectively in all species tested. However, watermelon was the most responsive (50% height reduction) and chrysanthemum was the least responsive (20% height reduction) to filtered light. Tomato and peppers had an intermediate response. In watermelons, total shoot dry weight was reduced over 25% compared to the control plants, with a progressive decrease in shoot weight as the dye concentration increased. The specific stem dry weight was gradually reduced as the dye concentration increased. Specific leaf dry weight was slightly reduced under filters, suggesting that smaller plants as opposed to a reduction in dry matter production primarily caused total dry weight reduction. Light transmitted through filters reduced percentage dry matter accumulation into stems from 27% to 18% and increased dry matter accumulation into leaves from 73% to 82%. Photoselective filters are effective in controlling height similarly to chemical growth regulators. Considering the PAR reduction by increase in dye concentration, a dye concentration that gives a light reduction of 25% or 35% may be optimum for commercial development of photoselective films.

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G.A. Picchioni, M. Valenzuela-Vazquez and S. Armenta-Sanchez

Lupinus havardii Wats. (Big Bend bluebonnet) has received considerable attention as a new specialty cut flower crop. We studied the consequences of Ca fertigation on growth, water use, and mineral nutrient uptake of L. havardii (`Texas Sapphire') for 88 days in a greenhouse. Four Ca concentrations were included (as CaCl2) in the fertigation solution at concentrations of 0, 2.5, 5.0, or 10.0 mm. Calcium supply did not affect the number of racemes produced per plant or total dry matter accumulation per plant. However, root dry matter accumulation, root: shoot ratio, net root mineral nutrient accumulation (milligrams P, K, Ca, Mg, and Fe per plant; micrograms Mn, B, and Cu per plant), and the preferential allocation of mineral nutrients to roots were influenced quadratically by CaCl2 supply, increasing up to 5.0 mm CaCl2 and then decreasing at 10.0 mm CaCl2. Lack of root sink response by plants exposed to 10.0 mm CaCl2 was associated with lowest daily rate of pot evapotranspiration, probably resulting from osmotic or Cl toxicity stress. Increased root sink strength for dry matter and mineral nutrients in response to CaCl2 supply up to 5.0 mm Ca is consistent with calcicole-like behavior and the native distribution of L. havardii on xeric, calcareous soils, where root growth and expansion favoring water and mineral nutrient acquisition may be of significant adaptive value for survival. The Carelated increase in root growth was reflected in up to a 5% to 20% increase in fertilizer P and K recovery per plant. Results indicate that Ca fertilization may be an effective horticultural strategy in greenhouse production of L. havardii, particularly for matching the natural edaphic habitat of the species and thus increasing efficiency of water and mineral nutrient management.

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G.A. Picchioni and C.J. Graham

Asimina triloba (L.) Dunal (pawpaw), a deciduous tree indigenous to the eastern U.S., is being considered as a potential new fruit crop. The difficulty in establishing transplanted pawpaw seedlings has been identified as an important research need for successful cultivation of this species. We have addressed the possible benefits of soil-applied CaSO4 in establishing pawpaw seedlings on acidic, low-Ca orchard soil. Two-year-old seedling rootstocks were planted at a spacing of 1.5 m (within rows) × 5.5 m (between rows), and trickle-irrigated (with N, P, and K) for two growing seasons. Before planting, CaSO4 was applied at rates of 0, 11, and 22 t/ha and incorporated to a depth of 15 cm. Seedling trunk cross-sectional area (TCA) growth increased with increasing CaSO4 application. After the first season, increases in TCA averaged 27% and 44% greater with CaSO4 treatments (11 and 22 t/ha, respectively), as compared to the 0 t/ha treatment. This effect was accentuated by the end of the second season. Average qualitative ratings (based on seedling vigor and appearance) were also improved with CaSO4 treatment. These findings indicate that establishment of pawpaw seedling rootstocks may be improved with Ca fertilization in orchards of low-Ca status. Additional data, including seedling dry matter accumulation, will be presented.

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Albert Liptay, Peter Sikkema and William Fonteno

The theme of this review is modulation of extension growth in transplant production through restraint of watering of the seedlings. The purpose of the modulation is to produce transplants of 1) appropriate height for ease of field setting and 2) adequate stress tolerance to withstand outdoor environmental conditions. Physiological responses of the plant are discussed in relation to the degree of water deficit stress and are related to the degree of hardening or stress tolerance development in the transplants. Optimal stress tolerance or techniques for measuring same have not been fully defined in the literature. However, stress tolerance in seedlings is necessary to withstand environmental forces such as wind and sand-blasting after the seedlings are transplanted in the field. It is also imperative that the seedlings undertake a rapid and sustained rate of growth after outdoor transplanting. Water deficit stress applied to plants elicits many different physiological responses. For example, as leaf water potential begins to decrease, leaf enlargement is inhibited before photosynthesis or respiration is affected, with the result of a higher rate of dry matter accumulation per unit leaf area. The cause of the reduced leaf area may be a result of reduced K uptake by the roots with a concomitant reduction in cell expansion. Severe water deficits however, result in overstressed seedlings with stunted growth and poor establishment when transplanted into the field. In transplant production systems, appropriate levels of water deficit stress can be used as a management tool to produce seedlings conducive to the transplanting process.

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P.P. David, C.K. Bonsi, E. Bonsi, R.D. Pace, O. Clark and L.C. Garner Carva

The effects of sequential foliage topping on two sweetpotato [Ipomoea batatas (L) Lam cvs Georgia Jet, TU-82-18921 cultivars were investigated in a field trial. Three initial foliage cuttings (15 cm cutting from the growing tip) were initialed at 45.60 and 75 days after planting (DAP). Each initial cutting date was followed by zero, one or two cuttings at biweekly intervals.

Total storage root yields were not affected by cutting treatments regardless of the cultivar investigated. Both cultivars differed in their response in dry matter accumulation, while Georgia Jet was not affected by cutting treatments, TU-82-1892 accumulated less dry matter when foliage tips were removed twice during the growth cycle (75.90 DAP) compared to all other cutting treatments.

The amount of foliage tips removed from each cultivar differed significantly over all treatment levels with Georgia Jet producing more foliage tips than TU-82-1892. However. production of foliage tips for both cultivars was greatest when foliage cutting was delayed until 75 DAP.

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R.M. Mirabello, A.E. Einert and G.L. Klingaman

The objective of this study was to examine the influence of mulch material and fertilizer application method on nutrient availability in a landscape situation. Beds containing four mulch materials (pine bark, cypress pulp, pine straw, and cottonseed hulls) and three fertilizer application methods (granule, liquid, and time release) were established. Fertilizer placement included application either above or below the mulch horizon. Beds with and without mulch cover and no fertilization were established as controls. Marigolds, Tagetes erecta `Hybrid Gold', were planted within the beds. Plants in unmulched or fertilized control beds had greater dry weights than plants in beds with mulch alone. Only plants grown in the cottonseed hull control demonstrated a slight improvement and cottonseed hulls demonstrated the best plant performance overall. The greater nitrogen content of cottonseed hulls may influence less immobilization of nitrogen in the soil solution during decomposition and reduce competition for nutrients between microorganisms and plants. Fertilization improved plant growth in all treatments except pine bark. Beds using pine bark showed significant reduction in plant dry matter accumulation. Potential toxicity or changes in soil chemistry by pine bark may have influenced these results and will be examined in further experiments. Fertilizer placement had no effect on plant growth.