The effect of exogenous ethylene was investigated on single-stemmed plants of Rosa L. `RUIdodo', `RUIrosora', `RUIjef', `MEIferjac', `MEIshulo', `MEIghivon' and `MEIgagul' grown in controlled environment growth chambers simulating summer-like and winter-like conditions. When the flower on each plant reached developmental stage 2 (showing color, calyx reflexing, no petals reflexed), the plants were placed for 18 h in plexiglass chambers with ethylene at 0, 0.1, 0.5, 1.0 and 5.0 μL·L-1 under a simulated interior environment at 21 °C with 14 μmol·m-2·s-1 fluorescent light. Under the same interior environment, the plants were kept for postharvest evaluation. Response to ethylene of all cultivars was not affected by the difference in growing conditions. As shown previously by other authors, however, the ethylene reduced flower longevity. Treatment with 0.1 μL·L-1 of ethylene reduced flower longevity by 1 day in comparison to the control (0 μL·L-1). The ethylene concentrations of 1.0 μL·L-1 and 5.0 μL·L-1 reduced flower longevity by 3 days. Regardless of ethylene concentration or growing conditions, `RUIjef' and `MEIferjac' exhibited the longest flower longevity and `MEIghivon' and `MEIgagul' the shortest flower longevity. All cultivars, except `RUIrosora', exhibited the longest flower longevity under summer-like vs. winter-like conditions, with the difference ranging from 1.5 to 5 days. `RUIrosora' exhibited similar flower longevity regardless of growing conditions. Differences in flower longevity in response to seasonal growing conditions have been found by us and other authors, but the cultivars used in this study have not been previously studied. This difference in flower longevity as a response to growing conditions cannot be explained by differences in response to ethylene so that other factors must be involved.
Jose Antonio S. Grossi, H. Brent Pemberton, and William E. Roberson
H. Brent Pemberton and Harold F. Wilkins
Florida-produced ‘Prize’ azalea plants were shipped to Minnesota with apical floral buds whose individual flowers had styles which had commenced elongating. These plants were ready for rapid forcing if given the traditional 6 weeks at 9°C. However, a single 2000 ppm GA (Pro Gibb3) spray treatment resulted in plants which flowered more rapidly without a traditional cold treatment when forced in a glasshouse under natural daylength (ND) in Minnesota during the spring and summer. Length of the ND in these experiments was considered critical, as plants forced in the spring and summer under an 8-hr short day (SD) treatment did not flower in a uniform manner, or floral abortion occurred in GA treated, uncooled plants forced during the autumn. Under ND conditions, extended to 20-hr by high pressure sodium, cool-white fluorescent or incandescent lamps, plants flowered more rapidly than those plants cooled at 9° for 6 weeks and forced under ND. Uniformity of flowering was enhanced and GA treatment had no effect when 3 weeks of 9° cooling preceded supplemental lighting treatments during autumn forcing. During winter, 20-hr of high pressure sodium + GA treatment or a SD treatment of noncooled plants resulted in more rapid, but similarly uniform flowering, when compared to plants with 6 weeks of cold treatment. These data provide evidence indicating that ‘Prize’ azalea floral buds may not exhibit a physiological dormancy.
Mason Marshall, Terri Starman, H. Brent Pemberton, and Calvin Trostle
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.
Brent K. Harbaugh, Mark S. Roh, Roger H. Lawson, and Brent Pemberton
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.
H. Brent Pemberton, Kevin Ong, Mark Windham, Jennifer Olson, and David H. Byrne
Rose rosette disease (RRD) is incited by a negative-sense RNA virus (genus Emaravirus), which is vectored by a wind-transported eriophyid mite (Phyllocoptes fructiphilus). Symptoms include witches broom/rosette-type growth, excessive prickles (thorns), discolored and distorted growth, and, unlike most other rose diseases, usually results in plant death. RRD is endemic to North America and was first described in Manitoba, Wyoming, and California in the 1940s. It has spread east with the aid of a naturalized rose species host and has become epidemic from the Great Plains to the East Coast of North America on garden roses in home and commercial landscapes where losses have been high. The disease was suggested to be incited by a virus from the beginning, but only recently has this been confirmed and the virus identified. The presence of the vector mite on roses has been associated with RRD since the first symptoms were described. However, more recently, the mite was demonstrated to be the vector of the disease and confirmed to transmit the virus itself. As a result of the RRD epidemic in North America and its effects on the national production and consumer markets for roses, a research team comprising five major universities (Texas, Florida, Tennessee, Oklahoma, and Delaware), a dozen growers and nurseries (all regions), six rose breeding programs (California, Wisconsin, Texas, and Pennsylvania), the major rose testing programs (Earth-Kind and AGRS), the major rose organization (American Rose Society), and the major trade organization AmericanHort has formed. This research project has been funded by the Specialty Crops Research Initiative through the U.S. Department of Agriculture (USDA) with the short-term objective of improving and disseminating best management practices (BMPs) and the long-term goal of identifying additional sources of resistance and developing the genetic tools to quickly transfer resistance into the elite commercial rose germplasm.
Carlos E. Bogran, H. Brent Pemberton, Thomas Isakeit, and William R. Roberson
A strain of Rhizoctonia solani was isolated from wax begonia (Begonia Semperflorens-Cultorum hybrids) plants in garden evaluation trial plots. This strain was then used to test for disease tolerance in a controlled environment experiment. Inoculated plants of 12 cultivars were evaluated for disease development and the area under the disease progress curve was calculated. No plants were disease free, but `Stara White', `Stara Pink', and three colors from the Party series exhibited greater disease tolerance than `Ambassador Coral', `Ambassador Deep Rose', and two experimental varieties. `Stara White', `Party Pink Bronze Leaf', and `Party White Bronze Leaf' were more tolerant than `Cocktail Vodka', an industry standard. When the same cultivars were grown in field garden evaluation plots, `Cocktail Vodka', four colors from the Stara series, and three colors from the Party series exhibited superior garden performance and flowering ratings to `Ambassador Coral' and an experimental `Rose' cultivar. For most cultivars, garden performance was correlated to disease tolerance. However, `Cocktail Vodka' exhibited good garden performance despite having a high level of disease in the inoculation experiment, indicating that other factors may be involved in determining garden performance.
H. Brent Pemberton, Yin-Tung Wang, Garry V. McDonald, Anil P. Ranwala, and William B. Miller
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.
Lisa Chen Cushman, H. Brent Pemberton, J. Creighton Miller Jr., and John W. Kelly
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.
Shannon E. Beach, Terri W. Starman, Kristen L. Eixmann, H. Brent Pemberton, and Kevin M. Heinz
Twenty-one cultivars of vegetative annuals were treated with 0%, 50%, or 100% of the production fertilization rate of 300 mg·L−1 N starting 2 weeks before and continuing until harvest. At harvest, plant width, flower number, and quality rating were measured. The plants were then placed in a simulated interior environment where flower number was counted and quality rating was assigned to each plant weekly for 3 weeks. Overall, 14% of the cultivars maintained a marketable quality (i.e., quality rating of ≥3.0 of 5) for 3 weeks, 43% for 2 weeks, 38% for 1 week, and one cultivar did not maintain quality during the postharvest evaluation. Reduced end-of-production fertilization rate (EPFR) resulted in higher quality ratings for at least one additional week of simulated shelf life for three cultivars, including ‘Dreamtime Copper’ bracteantha (Bracteantha bracteata), ‘Vanilla Sachet’ nemesia (Nemesia ×hybrida), and ‘Bridal Showers’ sutera (Sutera hybrida). ‘Comet White’ and ‘Sunlight’ argyranthemum (Argyranthemum frutescens) retained flowers an additional 2 weeks and ‘Caritas Lavender’ angelonia (Angelonia angustifolia), ‘Dreamtime Copper’ bracteantha, ‘Liricashowers Deep Blue Imp.’ and ‘Starlette Trailing Purple’ calibrachoa (Calibrachoa hybrid), ‘Vanilla Sachet’ nemesia, ‘Cascadias Pink’ petunia (Petunia ×hybrida), and ‘Bridal Showers’ sutera retained flowers an additional 1 week when treated with 0% compared with 50% or 100% EPFR. Four cultivars had decreased plant width at harvest with 0% EPFR. These results indicate that reducing fertilization 2 weeks before harvest can prolong shelf life of some vegetative annuals. Differences in the length of shelf life and responses to reduced EPFR occurred among cultivars of all the affected species. Reduced EPFR did not increase the shelf life of two species, including diascia (Diascia ×hybrida) and lantana (Lantana camara).
Garry V. McDonald, H. Brent Pemberton, Marvin L. Baker, and Jo Mondier
Liners of Rosa `MEIrutral' (=Red Sunblaze) were potted in 11.5-cm pots using Fison's Sunshine Mix no. 2 amended with 0%, 10%, 20%, or 30% composted poultry litter (PL) by volume. Plants were grown for 3 weeks before cutting back to 5 cm for final forcing (short-cycle) and were fertilized with 200 mg N/liter from 20N–8.9P–16.6K on a three feed and one leach schedule for the duration of the experiment. By flowering, plants growing in the 30% PL media were dead or stunted. However, there was little difference in total number of flowers, days to flower, and root and shoot dry weight between the other treatments. Media pH rose from 6.6 to 7.4 and EC rose from 0.7 to 6 millimhos with increasing PL content. This result alone could explain the poor growth in the highest PL rate treatment. However, tissue N levels were supraoptimal for the 20% and 30% PL rates, and tissue P levels were excessive for all PL rates. If a high-quality source of composted PL is available, it could be used as a media component for potted rose production at rates <20%, but monitoring of pH and EC and modifying fertilization techniques may be necessary to ensure success.