For a number of geophytic crops, pre-plant plant growth regulator (PGR) dips or soaks are an effective method of height control. Previous research has shown that a given PGR solution may be used to dip numerous bulbs without losing efficacy. What has been unknown is whether PGR solutions maintain efficacy over multiple-week (seasonal) time scales, especially if they have previously been used to treat bulbs. To address this question, 30 mg·L−1 flurprimidol solutions were prepared 3 weeks apart and used to dip narcissus and hyacinth bulbs and then held for 4 weeks at 17 °C in darkness. These solutions (now 7 and 4 weeks old) and a freshly prepared solution were used to dip bulbs of eight hyacinth and five narcissus cultivars. After appropriate cooling, bulbs were forced in a greenhouse. Results indicate no difference in growth reduction among the 0-, 4-, or 7-week-old solutions demonstrating no loss of PGR activity over a 7-week period. In two other experiments, 2.5, 5, and 10 mg·L−1 flurprimidol solutions were exposed to 0 to 8 days of full sun (late June) and then used to dip Lilium ‘Tresor’ bulbs for 1 minute. Growth of the plants indicated loss of growth regulation activity (taller plants) as the duration of exposure to sunlight increased, suggesting substantial photolysis of the active ingredient. Together, the results suggest that flurprimidol solutions can be held in darkness at 17 °C and used for at least 7 weeks without loss of efficacy.
William B. Miller
William B. Miller
Experiments conducted over 3 years have indicated the efficacy of preplant paclobutrazol or flurprimidol corm soaks for leaf and scape growth control in potted freesia (Freesia hybrida). A range of cultivars subjected to 30- to 60-min soaks in 60 to 120 mg·L−1 paclobutrazol and 10- to 30-min soaks in 10 to 30 mg·L−1 flurprimidol resulted in significant and commercially relevant height control without reducing the number of flowering scapes. Cultivars varied in their response to the plant growth regulators (PGRs), suggesting that individual grower trials will be necessary to develop an optimum treatment for each location.
Chris Watkins* and William B. Miller
The discovery and subsequent commercialization of 1-MCP has resulted in intense research interest around the world. A web site (http://www.hort.cornell.edu/mcp/) has been developed which provides a summary of the effects of 1-MCP on climacteric (18 species) and non-climacteric (6) fruits, vegetables (13), fresh cut produce (5), cut flowers and pot plants (more than 50 species has been created. The site is updated on a regular basis. For edible crops, most citations are available for apple (32 citations) and banana (21 citations). The ornamental literature is much less concentrated, and most crops are represented by a single citation. For all commodities, the majority of research has been focused on quality responses of the various products to 1-MCP, although increasingly 1-MCP is being used to investigate physiological and biochemical events associated with development, ripening and/or senescence.
Della Carbonaro and William B. Miller
Success in the production of seasonal flowering plants requires adequate knowledge of plant growth patterns and rates. In Easter lilies, pedicel growth is one the components of final plant height. Flower bud growth rates are important from the standpoint of timing of anthesis. To learn more about the localization of growth in Easter lily flower buds and pedicels, we conducted a time course experiment. Buds and pedicels were marked at 1.2 mm intervals using an inked bolt. Distances between ink marks were determined at 3 day intervals. Results indicate that 30 mm flower buds elongate almost exclusively from basal regions of the bud. The basal 1.2 mm segment elongated 16 mm in 20 days, while the apical 1.2 mm segment elongated 0.75 mm in the same period. Larger buds (initially 90 mm) gave similar results, although bud tip growth rate increased to some degree just prior to flowering. Pedicel elongation occurred almost exclusively at the apical end of the pedicel, adjacent to the region of greatest bud growth.
William B. Miller and Shi Niu
Sucrose is the major form of translocated carbohydrate in most plants. While enzymes of sucrose degradation have been well studied in many agronomic crop sinks, little is known about the physiology of sucrose breakdown in most floral tissues. Invertase and sucrose synthase are accepted as the key enzymes responsible for sucrose breakdown. As the first step in studying sucrose breakdown in Lilium longiflorum, we characterized floral bud invertase enzymes. Three soluble invertases were present in developing buds, and were resolved by DEAE-Sephacel chromatography (Invertases I, II, and III, in order of elution). After further purification, each enzyme was characterized. Each was an acid invertase (pH optima of 4.0 to 5.0). each had Km values for sucrose of 5.0 to 7.0 mM. To determine if the enzymes had tissue-specific localization, anthers were dissected from tepal, pistil, and filament tissues. Invertase I was localized primarily in anthers, with invertases II and III being present in much smaller amounts. Invertases II and III were the major forms in the other floral tissues with essentially no invertase I detectable.
William B. Miller and Erin Finan
Ethanol was demonstrated to reduce unwanted floral scape and leaf elongation of `Ziva' paperwhite narcissus (Narcissus tazetta) when plants were grown with traditional pebble culture. Root-zone ethanol concentrations of 1% to 5% (v/v) were effective in reducing height without visible phytotoxicity to the roots. Various ethanol sources, including gin, vodka, whiskey, schnapps, rum, and tequila, were equally effective in reducing growth when supplied at 4%; peppermint schnapps caused somewhat more growth inhibition, providing a safe, effective, and organic method for amateurs to control height of this popular flowering bulb. Beer and wine (white or red) were unsuitable for this use at 4% alcohol concentration.
Ricardo Campos and William B. Miller
The relationship between the activity of soluble acid invertase and metabolism of soluble carbohydrates was investigated in snapdragon flowers. Flowers were harvested at three different developmental stages, and at four different dates. Soluble carbohydrates were extracted and analyzed by HPLC; invertase activity was determined in crude enzyme extracts. Sucrose concentration slowly increased throughout flower development from a closed bud to a fully open flower. Fructose and glucose concentration were relatively lower at the bud stage, increased during petal elongation, then slightly decreased at flower maturity. Mannitol concentration showed little change during flower development. An unknown compound increased in concentration during petal elongation and decreased at maturity. For all harvest dates, the specific activity of acid invertase increased with flower development. These results show a positive correlation of invertase activity and hexose sugars accumulation. It is possible that at maturity sugars are metabolized at a faster rate than produced, causing a slight decline in hexose sugars.
Garry Legnani and William B. Miller
Experiments were conducted to evaluate effects of photoperiod on growth and dry-weight partitioning in Dahlia sp. `Sunny Rose' during both seedling (plug) production and subsequent production in 10-cm pots. Plugs were grown under short days [9-hour natural photosynthetic photon flux (PPF)] or long days (same 9-hour PPF plus a 4-hour night interruption with incandescent light). Total plant dry weight was unaffected by photoperiod; however, long days (LD) inhibited tuberous root development and increased shoot dry weight, fibrous root dry weight, leaf area, shoot length, and number of leaf pairs. Long days reduced plug production time by ≈1 week compared with short days (SD). Following transplanting to 10-cm pots, shoot growth and foliar development were superior under LD. There was no effect of photoperiod on foliar N concentration. The superior growth of LD plugs following transplanting can be attributed to the plant being in a physiological state conducive to shoot expansion instead of storage.
Judy Lee and William B. Miller
We determined the effects of preplant storage temperature and duration and greenhouse growing temperature on the growth and flowering of four cultivars of potted Ornithogalum representing Ornithogalum dubium (three cultivars) and Ornithogalum thyrsoides (one cultivar) originating from Israeli breeding. Bulbs were stored at five temperatures for 1 to 4 weeks before planting. Within the range of 9 to 27 °C, lower preplant storage temperature resulted in earlier flowering and taller plants, and for one cultivar, increased bulb respiration measured after storage. When bulbs were stored at 9 °C for 3 weeks, plants flowered at least 12 days earlier compared with controls stored at 27 °C. At 9 °C, as preplant bulb storage duration increased from 0 to 4 weeks, plants flowered more quickly and were taller. Within the range of 13 to 21 °C, 17 to 18 °C forcing temperatures gave the best combination of forcing time and plant quality.
Christopher B. Cerveny and William B. Miller
Ethylene effects were investigated on two tulip (Tulipa gesneriana L.) cultivars, Markant and Carreria. Pre-cooled bulbs were treated with ethylene (flow-through) for 1 week at 0, 0.1, 1.0, or 10 μL·L−1 (± 10%) in a modified hydroponic system. After ethylene exposure, plants were either destructively harvested for root measurements or forced in a greenhouse for flower measurements. Ethylene exposure at concentrations as low as 1 μL·L−1 during the first week of growth reduced shoot and root elongation and subsequently increased flower bud abortion. At 10 μL·L−1, root growth was essentially eliminated. In a second experiment, bulbs were treated overnight with 1-methylcyclopropene (1-MCP) before a 7-day exposure to 1 μL·L−1 ethylene. 1-MCP pretreatment eliminated the harmful effects of ethylene on root and shoot growth. This study illustrates the effects of ethylene exposure during hydroponic tulip production and demonstrates a potential benefit to treating bulbs with 1-MCP before planting.