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  • Author or Editor: Brent Pemberton x
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Rooted liners of pot rose (Rosa L.) cultivars Meiferjac, Meigagul, Meighivon, Meishulo, Ruijef, Ruidodo, and Ruirosora were used to study the influence of cultivar and seasonal growing environment on growth and postharvest performance. Single-shoot plants were grown in controlled environment chambers simulating summer (30 °C day/21 °C night cycle with a 14-hour photoperiod) and winter (21 °C day/16 °C night cycle with a 10-hour photoperiod) greenhouse growing conditions. At flower developmental stage 2 (showing color, calyx reflexing, no petals reflexed), the plants were placed in a continuously lighted simulated interior evaluation room at 21 ± 1 °C under 15 μmol·m-2·s-1 photosynthetic photon flux from cool-white fluorescent lamps for postharvest evaluations. Plants had quicker flowering, smaller flower diameter, more compact growth, and smaller leaf area when grown under the summer environment compared to the winter environment. Most cultivars exhibited greater flower longevity on summer-grown plants when compared to winter-grown ones. `Ruirosora' did not exhibit this difference due to exceptional longevity on winter-grown plants. Also, the use of single-shoot plants was shown to be a potentially useful way to increase replication in small growing environments such as growth chambers.

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Five cultivars of bare-root rose plants were exposed to increasing periods of drying and after rehydration were grown in containers until flowering in a plastic-covered greenhouse. At the start of the experiment, moisture content of well-hydrated roses was between 51% and 56%. Five or 7 h of drying resulted in moisture contents below 43% for four of the cultivars and caused up to 80% mortality, increased time to flower, and decreased the number of flowering shoots. ‘First Prize’ was most tolerant of drying conditions and all plants survived, whereas ‘Mister Lincoln’ plants were most susceptible and had poor regrowth performance. Whole-plant moisture of ‘Mister Lincoln’ was similar to that in the stem or shank, which means that aboveground components instead of the entire plant can be used for moisture determination.

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Forty-five rose genotypes including modem cultivars and rose species were evaluated in a field trial for resistance to black spot caused by Marssonina rosae. The trial was designed as a randomized block with four replications at two sites. The plots were planted at College Station (East Central Texas) and Overton (Northeast Texas). Ratings were done for the percentage of leatlets with black spot lesions and for leaf defoliation. These ratings were taken four times during the growing season from May to October 1993. Preliminary results indicate a high degree of resistance in the ten species studied, Modem cultivars were equally divided into moderate resistance, low resistance, and susceptible with only four showing high resistance. Disease pressure was higher and occurred earlier in the season at the Overton site. Disease pressure was highest at both sites in late spring and again in fall. Pressure was lowest in August after a prolonged period without rain. Introduction during the growing season of a previously unseen race of the pathogen was observed by the performance of the cultivar Sunbright.

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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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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%.

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Marigolds (Tagetes sp.) are ornamental plants with fine-textured, dark green foliage, and yellow, orange, or bicolored flowers. The relative salt tolerance of eight marigolds [‘Discovery Orange’, ‘Discovery Yellow’, ‘Taishan Gold’, ‘Taishan Orange’, and ‘Taishan Yellow’ african marigold (Tagetes erecta); ‘Hot Pak Gold’, ‘Hot Pak Orange’, and ‘Hot Pak Yellow’ french marigold (Tagetes patula)] was evaluated in a greenhouse experiment. Plants were irrigated weekly with nutrient solution at an electrical conductivity (EC) of 1.2 dS·m−1 (control) or saline solutions at an EC of 3.0 or 6.0 dS·m−1 (EC 3 or EC 6). Marigold plants began to show foliar salt damage (leaf burn and necrosis) at 6 weeks after the initiation of treatment. At harvest (9 weeks after the initiation of treatment), ‘Discovery Orange’, ‘Discovery Yellow’, ‘Taishan Gold’, and ‘Taishan Yellow’ plants exhibited severe foliar salt damage with visual scores less than 2 (on a scale of 0 to 5, with 0 = dead and 5 = excellent with no foliar salt damage) in EC 6. In the same treatment, ‘Hot Pak Gold’ and ‘Taishan Orange’ plants all died and only one of nine ‘Hot Pak Orange’ and ‘Hot Pak Yellow’ plants survived. In EC 3, all cultivars had slight or minimal foliar salt damage with visual scores ≈4 with the exception of Taishan Gold and Taishan Orange plants that showed moderate foliar damage with a visual score of 2.3 and 2.1, respectively. Treatment EC 3 reduced the flower number of ‘Discovery Orange’, ‘Discovery Yellow’, ‘Hot Pak Gold’, and ‘Hot Pak Yellow’ by 52%, 28%, 50%, and 30%, respectively, whereas EC 6 decreased the flower number of ‘Discovery Orange’ and ‘Discovery Yellow’ by 48% and 52%, respectively. In addition, both EC 3 and EC 6 did not reduce total dry weight (DW) of any cultivars, except Hot Pak Yellow and Taishan Yellow. In conclusion, all marigold cultivars are moderately sensitive to salt. ‘Discovery Orange’, ‘Taishan Yellow’, ‘Discovery Yellow’, and ‘Taishan Gold’ were more tolerant than ‘Hot Pak Gold’, ‘Hot Pak Orange’, ‘Hot Pak Yellow’, and ‘Taishan Orange’.

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Sunflower ‘Sunfinity’ (Helianthus hybrida) can be produced as a potted plant if apical dominance is removed with a manual pinch to control plant height and promote branching and flower number. Chemical pinching agents such as dikegulac sodium could prove to be valuable tools to reduce the labor and costs associated with manual pinching. Our objective was to determine the time of seedling growth and concentration of dikegulac sodium foliar spray application that would result in morphology similar to manually pinched plants. Dikegulac sodium was applied to sunflower ‘Sunfinity’ seedlings at one of four concentrations increasing from 200 to 500 mg⋅L−1 at the time of growth when the first, second, or third node (N1, N2, or N3) was the apical node and axillary stems at those nodes were undeveloped. Applications of 400 mg⋅L−1 at N3 and 500 mg·L−1 at N2 removed apical dominance because of total senescence of the apical meristem and produced a well-branched plant similar to that subjected to manual pinching. Apical dominance was temporarily inhibited without senescence of the apical meristem when 400 mg⋅L−1 was applied at N2 and when 500 mg⋅L−1 was applied at N3, which, nevertheless, resulted in branching that formed a well-rounded canopy.

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Three lisianthus [Eustoma grandiflorum (Raf.) Shinn.] cultivars 0, 10, 17, 24, or 31 days from sowing were grown in 28C soil for 0, 7, 14, 21, or 28 days to determine the effects of high temperature during seedling growth on the development of rosetted plants. Increasing the duration of high-temperature exposure increased the percentage of rosetted plants for all cultivars. Such exposure for 28 days resulted in 96%, 93%, and 18% rosetted plants for cultivars Yodel White, Yodel Pink, and GCREC-Blue, respectively. Seedling age did not affect percentage of flowering `Yodel Pink' plants, but as seedling age increased to 31 days, the percentage of flowering plants increased with `GCREC-Blue' and decreased for `Yodel White'. In a second experiment, four lisianthus cultivars were grown at 22C for 3 weeks and then exposed for 28 days to soil at 22, 25, 28, or 31C. Increasing soil temperature resulted in more rosetted plants for all cultivars. With soil at 31C, 83%, 58%, 19%, and 2% of the seedlings rosetted for the cultivars USDA-Pink, Yodel White, Little Belle Blue, and GCREC-Blue, respectively.

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Case-cooled bulbs of Lilium longiflorum `Nellie White' were forced to flowering. When the tepals on the first primary flower bud split, plants were placed at 2 °C in the dark for 0, 4, or 21 days. After storage, plants were placed in a postharvest evaluation room with constant 21 °C and 18 μmol·m-2·-1 cool-white fluorescent light. Lower leaves, upper leaves, and tepals of the first primary flower from a concurrent set of plants were harvested for carbohydrate analysis using HPLC. Storage time did not affect carbohydrate levels in the lower leaf or tepal samples, but sucrose and starch levels decreased while glucose and fructose levels increased in the upper leaf tissue with increasing storage time. These changes were correlated with a decrease in postharvest longevity for the first four primary flowers. Longevity of the fifth primary flower and total postharvest life of the five primary flowers was unaffected by storage.

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Simulated shipping (storage) experiments were conducted to determine the effects of shipping temperature and duration on flower longevity and leaf abscission of pot rose Rosa L. `Meijikatar' (= Orange Sunblaze) and `Meirutral' (= Red Sunblaze). In addition, three flower stages (1 = tight bud, calyx not reflexing; 2 = showing color, calyx reflexing, no petals reflexed; 3 = full color, petals beginning to reflex, traditional bud stage) were selected immediately prior to storing plants at 4, 16, or 28 °C for 2, 4, or 6 days. The experiment was conducted during the summer and repeated during the winter. Evaluations were made in an interior environment at 21 °C for both experiments. `Meirutral' exhibited longer poststorage longevity and less leaf abscission than `Meijikatar' in both experiments. Flowers of both cultivars advanced by about one stage during storage at temperatures greater than 4 °C in summer, but developed more slowly in winter. Results from both experiments showed that plants stored at 4 °C had the longest poststorage floral longevity, the best flower quality, and the least leaf abscission, regardless of cultivar, storage duration, or flower stage at the beginning of storage. For plants stored at 16 °C, floral longevity decreased and leaf abscission increased when the duration was longer than 4 days. At 28 °C, flower longevity decreased and leaf abscission increased, especially at durations longer than 2 days. In the winter experiment, there was no leaf abscission on plants placed in the dark at 21 °C and watered during storage treatments lasting up to 6 days. In the summer experiment, the younger the flower, the more it was negatively affected by high storage temperature. Overall, poststorage floral longevity was longer in the summer than the winter experiment.

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