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Xiaoya Cai, Terri Starman, Genhua Niu and Charles Hall

irrigating plants based on water requirements, water use could be reduced, and plants may be acclimated for drought tolerance in the landscape ( Kozlowski and Pallardy, 2002 ). Roses ( Rosa hybrida L.) are some of the most popular garden plants in the world

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Malgorzata Serek

The postharvest quality of miniature pot roses is limited by bud abscission and premature flower senescence. Rosa hybrida `Victory Parade' plants were treated with ethephon to study their sensitivity to ethylene and with silver thiosulfate (STS) to investigate its inhibitory effects on ethylene action. Bud abscission and flower senescence were promoted by spraying plants with ethephon, and the longevity of individual flowers and whole plants was reduced. All STS concentrations (0.4, 0.8, 1.2, 1.6 mM improved postharvest keeping quality. Bud abscission and flower senescence were decreased and the longevity of flowers and whole plants was improved by applying STS. Chemical name used: 2-chloroethylphosphonic acid (ethephon).

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Margaret J McMahon and John W. Kelly

The growth of Rosa × hybrida and Exacum affine under different spectral filters was evaluated. Three filters that altered light quality were developed. One, a red textile dye, filtered out much of the blue/green portion of the light spectrum but did not change far-red to red (FR/R) light ratio. Another, a blue textile dye, raised FR/R by filtering out a portion of red light. The third, a salt (copper sulfate) lowered FR/R by filtering out a greater portion of far-red than red light. Two controls were used that did not alter light quality. The filters were installed in specally built growth chambers. Photosynthetic Photon Flux Density (PPFD) was adjusted to equal values in each chamber.

Plants of both species were significantly shorter and had higher leaf chlorophyll, when grown under the low FR/R filter.

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David G. Clark and John W. Kelly

Rosa × hybrida `Meijikatar' plants were fertilized on weekdays with Hoagland's solution at 100, 200, or 300 mg·liter-1 nitrogen. Prior to simulated shipping, plants were treated with benzyladenine at 0, 25, 50, or 100 mg a.i.·liter-1. Plants were subsequently paper sleeved and stored in cardboard boxes in darkness at 16 C for 5 days.

On the day of harvest, plant height and number of flowers per plant were not affected by production nitrogen level. After removal from simulated shipping, total chlorophyll was increased in the lower leaves of plants grown at higher nitrogen rates and treated with higher rates of benzyladenine. Three and five days after removal from simulated shipping, the least percent leaf chlorosis was observed on plants treated with higher rates of cytokinin, but there was no effect of production nitrogen regime.

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David G. Clark and John W. Kelly

Rosa × hybrida `Meijikatar' plants were fertilized on weekdays with Hoagland's solution at 100, 200, or 300 mg·liter-1 nitrogen. Prior to simulated shipping, plants were treated with benzyladenine at 0, 25, 50, or 100 mg a.i.·liter-1. Plants were subsequently paper sleeved and stored in cardboard boxes in darkness at 16 C for 5 days.

On the day of harvest, plant height and number of flowers per plant were not affected by production nitrogen level. After removal from simulated shipping, total chlorophyll was increased in the lower leaves of plants grown at higher nitrogen rates and treated with higher rates of benzyladenine. Three and five days after removal from simulated shipping, the least percent leaf chlorosis was observed on plants treated with higher rates of cytokinin, but there was no effect of production nitrogen regime.

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Virginia S. Story, Douglas A. Hopper and Troy T. Meinke

Two-year-old Rosa hybrida L. `Royalty', `Emblem', and `Samantha' plants were pinched 20 Oct. and 28 Dec. 1992 for Christmas and Valentine's Day crops. At 10 and 25 days after pinch, and at flowering, 5 shoots from each bench location were destructively sampled for leaf (node) number, stem diameter, stem length, and fresh and dry weights of stem, leaves, and flower bud. Time to visible bud, to color, and to flower from pinch were also recorded.

Results were tabulated; an analysis of variance showed that the three rose cultivars produced flowers which were not significantly different within crops but were different between seasonal crops. The Christmas `Royalty' crop produced more flowers (but also more blind shoots) than did the Valentine's Day crop. Days to flower, stem diameters, and stem lengths were similar within and between crops for all cultivars. Total fresh and dry weights for all three cultivars tended to be greater for the Valentine's Day crop than for the Christmas crop. The seasonal photosynthetic photon flux (PPF) variation may account for these differences.

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Douglas A. Hopper, P. Allen Hammer and James R. Wilson

This paper details the development and verification of ROSESIM, a computer simulation model of the growth of `Royalty' roses (Rosa hybrida L.) based on experimentally observed growth responses from pinch until flowering under 15 combinations of constant photosynthetic photon flux (PPF), day temperature (DT), and night temperature (NT). Selected according to a rotatable central composite design, these treatment combinations represent commercial greenhouse conditions during the winter and spring in the midwestern United States; each selected condition was maintained in an environmental growth chamber having 12-hour photoperiods. ROSESIM incorporates regression models of four flower development characteristics (days from pinch to visible bud, first color, sepal reflex, and flowering) that are full quadratic polynomials in PPF, DT, and NT. ROSESIM also incorporates mathematical models of nine plant growth characteristics (stem length and the following fresh and dry weights: stem, leaf, flower, and total) based on data recorded every 10 days and at flowering. At each design point, a cubic regression in time (days from pinch) estimated the plant growth characteristics on intermediate days; then difference equations were developed to predict the resulting daily growth increments as third-degree polynomial functions of days from pinch, PPF, DT, and NT. ROSESIM was verified by plotting against time each simulated plant growth characteristic and the associated experimental observations for the eight factorial design points defining the region of interest. Moreover, one-way analysis of variance procedures were applied to the differences between ROSESIM predictions and the corresponding observed means for all 15 treatment combinations. At 20 days from pinch, significant differences (P < 0.05) were observed for all nine plant growth characteristics. At 30 and 40 days from pinch, only flower fresh and dry weights yielded significant differences; at flowering, none of the 13 selected responses yielded significant differences. These graphical and statistical comparisons provide good evidence of ROSESIM's ability to predict the growth response of `Royalty' roses over a wide range of constant environmental conditions.

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Douglas A. Hopper and P. Allen Hammer

A central composite rotatable design was used to estimate quadratic equations describing the relationship of irradiance, as measured by photosynthetic photon flux (PPF), and day (DT) and night (NT) temperatures to the growth and development of Rosa hybrida L. in controlled environments. Plants were subjected to 15 treatment combinations of the PPF, DT, and NT according to the coding of the design matrix. Day and night length were each 12 hours. Environmental factor ranges were chosen to include conditions representative of winter and spring commercial greenhouse production environments in the Midwestern United States. After an initial hard pinch, 11 plant growth characteristics were measured every 10 days and at flowering. Four plant characteristics were recorded to describe flower bud development. Response surface equations were displayed as three-dimensional plots, with DT and NT as the base axes and the plant character on the z-axis while PPF was held constant. Response surfaces illustrated the plant response to interactions of DT and NT, while comparisons between plots at different PPF showed the overall effect of PPF. Canonical analysis of all regression models revealed the stationary point and general shape of the response surface. All stationary points of the significant models were located outside the original design space, and all but one surface was a saddle shape. Both the plots and analysis showed greater stem diameter, as well as higher fresh and dry weights of stems, leaves, and flower buds to occur at flowering under combinations of low DT (≤ 17C) and low NT (≤ 14C). However, low DT and NT delayed both visible bud formation and development to flowering. Increased PPF increased overall flower stem quality by increasing stem diameter and the fresh and dry weights of all plant parts at flowering, as well as decreased time until visible bud formation and flowering. These results summarize measured development at flowering when the environment was kept constant throughout the entire plant growth cycle.

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D.G. Clark and J.W. Kelly

Potted Rosa × hybrida `Meijikatar' plants were produced at 350, 700, and 1050 μl·liter-1 CO2. At a stage of development where half of the flowers showed color, plants were placed into simulated shipping incubators for 5 days at 4 or 16 C.

Increased CO2 levels resulted in shorter production time, increased root dry weight, increased plant height, and reduced total chlorophyll in the upper leaves of the plants. Upon removal from simulated shipping, the number of etiolated shoots per plant increased with increased CO2 concentration. After 5 days in a simulated interior environment, higher shipping temperatures induced more leaf chlorosis, but there were no differences in leaf chlorosis due to CO2 enrichment.

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Niels B. Bredmose

The cut rose, grown as a single-stemmed crop, resembles a potted plant and can be adapted to transportable bench systems. Potentially, this cultivation method could increase control of rose development, flexibility of production and produce, and automation of difficult or laborious cultural operations. Synchronous growth and flowering is considered important. The effects of increased quantum irradiation integral and plant density on shoot growth, fresh biomass production, and bloom quality were studied as single-stemmed rose plants (Rosa hybrida L.) `Kordapa' Lambada, `Tanettahn' Manhattan Blue, `Tanorelav' Red Velvet, and `Sweet Promise' Sonia grown under 20 hours photoperiods at 23 °C average air temperature. Plants were grown in rockwool cubes on ebb and flood benches irrigated with a complete nutrient solution, and were supplied with carbon dioxide at 1000 μmol·mol-1. Increased the daily quantum integral from 17.8 to 21.0 mol·m-2·d-1 increased fresh biomass efficiency, stem diameter, and specific fresh mass while number of nodes, number of five-leaflet-leaves, plastochron value, and stem length at anthesis decreased. Fresh mass at anthesis was not affected by the treatments. Increasing plant population density from 100 to 178 plants/m2 increased stem length at visible flower bud, and reduced both fresh biomass efficiency and specific fresh mass. These effects are suggested to be related to assimilate supply and translocation, and light perception of the roses. High quantum integral slightly reduced flower diameter but in general, quantum integral or plant density did not affect bloom quality or vase life. Use of preservative floral solution generally improved rose flower diameter and vase life. In Lambada increased light quantum integral prolonged vase life, but use of preservative solution did not. The cultivars Sonia and Red Velvet required 19 to 20 days from cutting/planting until onset of bud growth, 29 to 34 days until visible flower bud, and 39 to 49 days until anthesis. Red Velvet roses were ≈60 cm long at anthesis, and had larger stem diameter and growth rate, accumulated more fresh biomass, were most efficient producing fresh biomass, and had higher specific fresh mass among the cultivars. Light quantum integral is suggested to be used as a means to synchronize single-stemmed rose plant development.