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Xiaoya Cai, Terri Starman, Genhua Niu, Charles Hall, and Leonardo Lombardini

A greenhouse study was conducted to evaluate the response of four garden roses (Rosa ×hybrid L.), ‘RADrazz’, ‘Belinda’s Dream’, ‘Old Blush’, and ‘Marie Pavie’, to drought stress. Plants grown in containers were subjected to two watering treatments, well-irrigated [water as needed: ≈35% substrate moisture content (SMC) at re-watering] and cyclic drought stress (withholding irrigation until plants exhibit incipient wilting: ≈10% SMC, then re-watering to field capacity for subsequent dry down). Shoot growth and flower number were reduced in the drought treatment compared with the well-irrigated plants in all cultivars with least reduction in ‘RADrazz’. Drought stress reduced root growth in ‘Belinda’s Dream’ and ‘Marie Pavie’, whereas there was no difference in root growth in ‘RADrazz’ and ‘Old Blush’. Decreased SMC induced reduction in net photosynthetic rate (Pn), stomatal conductance (g S), transpiration rate (E), and midday leaf water potential (ψ). Leaf water use efficiency (WUE) increased as SMC decreased in all cultivars. However, the relationship between these physiological parameters and SMC differed among the cultivars. At SMC between 10% and 20%, ‘RADrazz’ had higher Pn, g S, E, and WUE compared with the other three cultivars. Therefore, ‘RADrazz’ was the most drought-tolerant during container production among the cultivars investigated. With lower gas exchange rates and greater reduction in flower number at low SMC, ‘Marie Pavie’ was less drought-tolerant compared with the other three cultivars.

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Terri Woods Starman, Teresa A. Cerny, and Amy J. MacKenzie

The productivity and profitability of annual and perennial field-grown specialty cut-flower species were evaluated for the southeastern United States. Data were collected on 20 annuals and 20 perennials in 1992 and on 19 annuals and 19 perennials (10 in their second year of production) in 1993. Productivity and profitability were based on yield and stem length measurements. Yield was expressed as total number of stems harvested. Income per 30-cm center was predicted from the number of stems ≥41 cm long that were harvested. Some species had high yields but stem lengths were too short for most market outlets. Among those species that combined high yield with long stems and resulted in high profitability without major pest or postharvest problems were the perennials Achillea filipendulina Lam., Echinacea purpurea (L.) Moench, Liatris spicata (L.) Willd., and Platycodon grandiflorus Jacq. A. DC. and the annuals Antirrhinum majus L., Cosmos bipinnatus Cav., Scabiosa atropurpurea L., and Zinnia elegans Jacq. Low overhead of field production coupled with productive species could prove to be profitable.

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Linda F. Meer, James E. Faust, and Terri Woods Starman

An experiment was conducted to determine the effect of plant growth regulator, application concentration, and time of application on five cultivars of Kalanchoe (Stromboli, Majestic, Heirloom, Keepsake, and Revelry). Kalanchoe cuttings were propagated in 5.2-cm-diameter containers under a short-day photo-period, then placed into a greenhouse maintained at 20C. Spray applications of paclobutrazol (25 or 50 ppm) and uniconazole (1 or 5 ppm) were made prior to visible flower bud (VB), after VB, or before and after VB. Across all cultivars and spray application dates, paclobutrazol applied at 25 and 50 ppm reduced total plant height by 20% and 29%, respectively, while uniconazole applied at 1 and 5 ppm reduced total plant height by 16% and 24%, respectively. Plant height was reduced by 13% with the pre-VB application, 23% with the post-VB application, and 32% with the pre- and post-VB applications. In general, the greater the treatment effectiveness at reducing plant height, the greater the increase in time to flower. For example, a post-VB Bonzi (50 ppm) application caused a 6-day delay in time to first open flower. With the appropriate plant growth regulator application, all five Kalanchoe cultivars tested could be used for commercial production in 5.2-cm-diameter pots.

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Amy J. MacKenzie, Terri W. Starman, and Mark T. Windham

Trichoderma harzianum is a well-documented biocontrol agent that has been shown to enhance rooting of chrysanthemum `White Marble'. The objective of this research was to determine if T. harzianum would enhance rooting of hard-to-root chrysanthemum cuttings. Two hard-to-root cultivars (`Dark Bronze Charm' and `Golden Bounty') and two easy-to-root cultivars (`Davis' and `White Marble') were propagated in a 1:1 peat-perlite medium amended with T. harzianum at a rate of 0, 5, or 25g/kg medium. Measurements were taken 7, 14, and 21 days after insertion of the cuttings into the medium. Interactions occurred between rate of amendment and day of measurement for some variables measured. However, overall there was increased root fresh and dry weight of all cultivars when T. harzionum rates were 5 or 25 g/kg medium. Increased root fresh and dry weight occurred on days 14 and 21 for most cultivars. Root fresh and dry weight increased with increasing rate of amendment on day 14 but there was no difference between the 5 and 25 g/kg rates on day 21. Shoot fresh weight was increased with 5 or 25 g/kg each measurement day for all cultivar except `White Marble' and shoot length was increased with 25g/kg for all cultivars.

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Rebecca G. Bichsel, Terri W. Starman, and Yin-Tung Wang

Experiments were conducted to determine how nitrogen (N), phosphorus (P), and potassium (K) rate and fertilizer termination time affect the growth and flowering of a Dendrobium nobile Lindl. hybrid, Dendrobium cv Red Emperor ‘Prince’. Nitrogen, P, and K were tested in separate experiments as a factorial combination of five rates and three termination dates (1 Sept., 1 Oct., and 1 Nov. 2005). Nitrogen and K rates were 0, 50, 100, 200, and 400 mg·L−1. Phosphorus rates were 0, 25, 50, 100, and 200 mg·L−1. Levels of the nutrients not being tested were held constant. For all nutrients, ending fertilization on 1 Sept. resulted in greater or similar pseudobulb thickness compared with ending fertilization on 1 Oct. or 1 Nov. Pseudobulbs grew taller as the N rate increased, peaking at 100 and 200 mg·L−1. There were interactions between the N rate and fertilizer termination time on all reproductive characteristics. For all fertilizer termination times, flower number increased once N was applied. When ended on 1 Nov., 200 and 400 mg·L−1 N caused a delay to reach anthesis. All P rates resulted in taller plants with equally more nodes when compared with 0 mg·L−1. As the K rate increased from 0 to 100 mg·L−1, plant height increased, with no further increase at higher rates. The number of leaves remaining increased as N and K rates increased up to 200 mg·L−1. Total flower number and flowering node number increased as the K rate increased to 100 mg·L−1 (terminated on 1 Sept.) or 50 mg·L−1 (terminated on 1 Oct. or 1 Nov.). In the fourth experiment, only N was ended at four termination times, whereas all other nutrients continued to be supplied until flowering. Control plants received all fertilizer elements until flowering. The duration of N application did not affect vegetative or flowering characteristics. No aerial shoots were observed as a result of prolonged application of N at all rates. In summary, 100 mg·L−1 N, 25 mg·L−1 P, and 100 mg·L−1 K are recommended for optimal vegetative growth and reproductive development of Dendrobium cv Red Emperor ‘Prince’.

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Terri W. Starman, Shannon E. Beach, and Kristen L. Eixmann

Twenty-one cultivars from nine species of vegetative annuals were grown under optimum greenhouse production practices until maturity. At harvest, they were subjected to 0, 1, or 2 days of simulated shipping. After shipping, plants were rated for quality, and flower abscission was counted postship and weekly for 3 weeks in a simulated retail environment. There were few decreases in flower number and quality directly postship, but decline symptoms became evident as time lapsed in the postharvest environment. Flower abscission resulting from increased shipping duration occurred on ‘Sun Chimes Coral’ diascia (Diascia ×hybrida) and ‘Aromatica White’ nemesia (Nemesia ×hybrida). During the postharvest evaluation, ‘Dreamtime Copper’ bracteantha (Bracteantha bracteata), ‘Superbells Trailing Blue’ calibrachoa (Calibrachoa hybrid), ‘Aromatica White’ nemesia, and ‘Candy Floss Blue’ sutera (Sutera cordata) were the only cultivars to abscise all flowers (<0.4 flowers) by the end of the first week. Five cultivars still had flowers at termination of the experiment. Of these five, four were bracteantha cultivars including ‘Florabella White’, ‘Florabella Gold’, ‘Dreamtime Cream’, and ‘Sundaze Golden Yellow’, and ‘Cascadias Pink’ petunia. After 2 weeks postharvest, 12 of the 21 cultivars that were shipped 1 or 2 days did not have a high enough quality rating (<3.0 points) to be considered marketable. Each species in this study had one or two postharvest decline symptoms common to all cultivars of that species. However, cultivars within species also varied in their postharvest decline symptoms and longevity. More optimum environmental conditions, better care, and faster turnover in the retail market are needed to improve shelf life of vegetative annuals sold in containers.

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Terri W. Starman, Melissa C. Robinson, and Kristen L. Eixmann

Plant response to ethephon treatment was tested on 27 cultivars of vegetative annuals that have spreading and trailing growth habits. A control treatment was compared to 500 and 1000 mg·L-1 (ppm) foliar spray treatments of ethephon. Plant height and/or width index were significantly reduced for 81% of the cultivars tested. Responsive cultivars were alternanthera (Alternanthera dentata), brachyscome (Brachyscome iberidifolia) `Toucan Tango'; calibrachoa (Calibrachoa hybrids) `Colorburst Red', `Million Bells Cherry Pink', and `Trailing Pink'; diascia (Diascia × hybrida) `Sunchimes Rose' and `Red Ace'; double impatiens (Impatiens wallerana) `Tioga Red' and `Tioga White'; sweetpotato vine (Ipomoea batatas) `Sweet Caroline Bronze'; lantana (Lantana camara) `Patriot Cherry' and `Samantha'; nemesia (Nemesia × hybrida) `Aromatica Dark Lavender', `Blue Bird', and `Blueberry Sachet'; nolana (Nolana paradoxa) `Blue Eyes'; ivy geranium (Pelargonium hybrida) `King of Balcon'; petunia (Petunia × hybrida) `Cascadia Pink', `Mini Bright Pink', and `Supertunia Mini Purple'; bacopa (Sutera cordata) `Bridal Showers'; and vinca vine (Vinca minor) `Illumination'. Ethephon was not effective on monopsis (Monopsis unidentata) `Royal Flush', persicaria (Persicaria microcephala) `Red Dragon', or calibrachoa `Liricashower Rose'. Different cultivars of petunia showed varied responses to ethephon treatments as did trailing snapdragon (Antirrhinum majus) `Chandelier Yellow' and `Luminaire Yellow'. Flower number was reduced in 55% of the cultivars due to a delay in flowering. The experiment finds efficacy of ethephon for most cultivars treated at rates greater than or equal to that used commercially, however more research is needed to determine optimum concentrations for the specific cultivars. Chemical name used: ethephon [(2-chloroethyl) phosphonic acid].

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Terri Woods Starman, Teresa A. Cerny, and Tracy L. Grindstaff

Height control and flowering responses to uniconazole spray or drench treatments were measured for `Multibloom Scarlet' and `Red Elite' geranium (Pelargonium ×hortorum L.H. Bailey). Total plant height of both cultivars was reduced proportionately to the height of a 10-cm container when the uniconazole drench concentration was 0.025 mg a.i./pot. Used as a spray, uniconazole was not as effective in restricting total plant height of either cultivar. Foliage height was shortened more than inflorescence height. Inflorescence diameter was decreased with increasing uniconazole drench concentrations. Sprays did not affect inflorescence diameter of either cultivar. Uniconazole effect on days to flower varied with cultivar and application method. Chemical name used: (E)-(S)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-pent-1-ene-3-ol (uniconazole).

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Ockert Greyvenstein, Brent Pemberton, Terri Starman, Genhua Niu, and David Byrne

The decline in sales of garden roses can, in part, be attributed to the lack of well-adapted cultivars. Successful selection for any trait requires an accurate phenotyping protocol. Apart from field screening, a protocol for phenotyping high-temperature tolerance in garden roses is yet to be established. An experiment was conducted to determine the stage of development when flowers were most sensitive to high-temperature stress. Liners of Rosa L. ‘Belinda’s Dream (BD) and the Knock Out® rose ‘RADrazz’ (KO) were planted in a soilless medium and grown in a greenhouse. Established plants were pruned retaining several nodes with leaves on two main shoots and treatments started. The experiment was conducted in growth chambers held at either 24/17 °C (control) or 36/28 °C (stress) day/night temperatures. Six time and duration temperature treatments included 8 weeks of continuous control conditions, 8 weeks of continuous stress conditions, and four sequential 2-week high-temperature shock treatments. Continuously stressed plants flowered in the least amount of days but did not differ from the continuous control-treated plants based on nonlinear thermal unit accumulation until flowering. Both cultivars had a 70% reduction in flower dry weight under continuous stress conditions. Flowers were most sensitive to high-temperature stress at the visible bud stage, which corresponds to Weeks 5 to 6 and Weeks 7 to 8 for BD and Weeks 3 to 4 and Weeks 5 to 6 for KO, respectively. KO was more resistant to flower abscission than BD when treated at the visible bud stage, but no difference in flower dry weight reduction between BD and KO was found. The number of vegetative nodes to the flower was unaffected by treatment and differed between the cultivars.

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Ockert Greyvenstein, Terri Starman, Brent Pemberton, Genhua Niu, and David Byrne

The decline of garden rose sales over the past 20 years can be partially attributed to the lack of material adapted to a wide range of landscapes, which includes adaptation to high temperature stress. Current methods for evaluating high temperature susceptibility in garden roses are based on field observations, which are time consuming and subjected to ever-changing environmental conditions. A series of experiments were conducted to optimize protocols and compare the use of chlorophyll fluorescence (CFL) and cell membrane thermostability (MTS) by way of electrolyte leakage as methods to screen for high temperature susceptibility. Immature leaves proved better than mature leaves for both CFL and MTS measurements, using either detached leaf or whole plant stress assays. MTS measured on immature leaves stressed in a water bath at 50 °C for 45 minutes proved most consistent in separating rose clones based on high temperature susceptibility. Stressing actively growing plants with flower buds of 2 mm in diameter in a heat chamber at 44 °C for 3 hours resulted in increased flower abscission and leaf necrotic lesions on more susceptible clones when compared with those that were heat tolerant. Combining MTS measurements from immature leaves stressed in a water bath with the flower abscission and leaf necrosis responses 10 days after stress in a heat chamber could be the first step to screen and select against the more susceptible clones in a garden rose breeding program. Power analyses suggest that the proposed MTS protocol would be efficient in detecting differences between clones when the difference in electrolyte leakage is greater than 10%.