Many plants have mechanisms of physical or chemical resistance that protect them from herbivores in their environment. Vertebrates such as meadow voles (Microtus pennsylvanicus) cause significant damage to ornamental plantings and home gardens. Our goal was to identify flowering bulbs that could be used to design more herbivore-resistant home landscapes. Single-choice feeding trials with captive prairie voles (Microtus ochrogaster) were used to assess the relative resistance of 30 bulb varieties to deter rodents from consuming fresh plant material and freeze-dried, powdered bulb mixed with a preferred food (applesauce). Each fresh bulb and dried-bulb/applesauce mix was offered twice to 12 to 15 pairs of adult prairie voles. Bulb varieties that resulted in the lowest mean consumption were assumed to be the most resistant to feeding activity. With fresh bulbs, only tulips (Tulipa spp.) exhibited no resistance to prairie vole feeding. Dried-bulb/applesauce mixes containing hyacinth (Hyacinth spp.), crocus (Crocus spp.), corn leaf iris (Iris bucharica), dutch and dwarf iris (Iris reticulata), onion (Allium spp.), and squill (Scilla siberica) were also readily consumed, and thus, these bulbs could be damaged at sites with high rodent activity. Daffodil (Narcissus spp.), painted arum (Arum italicum), camass (Camassia leichtlinii), glory-of-the-snow (Chinodoxa forbesii), autumn crocus (Colchicum spp.), crown imperial (Fritillaria imperialis), persian fritillaria (Fritillaria persica), snowdrop (Galanthus nivalis), and grape hyacinth (Muscari armeniacum) bulbs were resistant to prairie vole feeding in both forms (fresh bulbs and dried-bulb/applesauce mixes). Consequently, all of the specialty flower bulbs tested, except tulip, exhibited some resistance to prairie vole feeding in their fresh form, and could be suitable for designing herbivore-resistant landscapes.
Paul D. Curtis, Gwen B. Curtis, and William B. Miller
Susan E. Trusty, William B. Miller, and Dale Smith
In order to more fully understand flower growth and development, we are interested in carbohydrate partitioning and metabolism in floricultural crops. In recent work with Chrysanthemum, we noted the occurrence of several early-eluting carbohydrate peaks (as detected by HPLC with a resin-based column in the calcium form). These peaks were present in flowers and stems, and in lesser amounts in leaves. Acid hydrolysis of the unknowns liberated large amounts of fructose and much smaller amounts of glucose, indicating that these peaks are fructans, or medium chain-length fructose polymers. Fructans represented 10% and 25% of the carbohydrate in a 12:5:3 methanol: chloroform: water extract of leaves and stems, respectively. Flower petals were extracted with 95%. ethanol, then with water. Fructans accounted for more than 40'% of the water soluble carbohydrate in flower bud tissue. It is likely that fructans serve as a major reserve carbohydrate in Chrysanthemum. Additional studies are underway to better characterize flower petal fructans, and to understand their role in flower development.
Kelly J. Prevete, R. Thomas Fernandez, and William B. Miller
Drought stress durations of 2, 4, and 6 days were imposed on Boltonia asteroides `Snowbank', Eupatorium rugosum, and Rudbeckia triloba to determine the effects on carbohydrate partitioning in the plant. Drought stress was imposed on 19 Sept. 1997 on 1.9-L containerized plants. Plants were planted in the field the day following release from stress. Crown and leaf samples of the three species were collected 21, 23, 25 Sept. 1997 and 30 Jan. and 4 May 1998 and were analyzed for low molecular weight sugars and fructans. The species differed in the time it took for longer chain fructans to break down to shorter chain fructans and low molecular weight sugars (glucose, fructose). The drought tolerant Boltonia and Rudbeckia had shifts from longer chain to shorter chain fructans by day 4 of stress. Boltonia had a change in carbohydrate partitioning in the leaf tissue, while Rudbeckia had a change in crown tissue carbohydrate partitioning. Eupatorium did not have a shift in longer chain fructans to shorter chain fructans in crown tissue until day six of stress. The slower shift from longer chain fructans to shorter chain fructans by Eupatorium, compared to Boltonia and Rudbeckia, could explain the lack of drought tolerance of Eupatorium. The shift from high molecular weight sugars to low molecular weight sugars suggests that the higher molecular weight sugars broke down to lower molecular weight sugars in response to drought stress.
Anil P. Ranwala, Garry Legnani, and William B. Miller
Several experiments were conducted to find effective ways of utilizing gibberellin4+7 (GA4+7) and benzyladenine (BA) to prevent leaf chlorosis during greenhouse production of Easter lilies (Lilium longiflorum Thunb.) while minimizing the undesirable side effects on stem elongation. On an absolute concentration basis, GA4+7 was much more effective than BA in preventing leaf chlorosis. Excessive levels of GA4+7, however, tended to cause stem elongation. When applied at around the visible bud stage, if the foliage was well covered with the spray solution, 25 mg·L-1 of GA4+7 was adequate for maximum protection against leaf chlorosis. Increasing the GA4+7 concentration above 25 mg·L-1 gave no additional benefit on leaf chlorosis. Two possible modes of GA4+7 uptake during a foliar spray application (absorption through leaves and stems, and root uptake of the extra run-off) were studied in terms of their relative contribution to leaf chlorosis and stem elongation. Although both modes of uptake prevented leaf chlorosis, foliar uptake was much more effective than root uptake. However, GA4+7 taken up by the roots contributed mainly to stem elongation. When sprayed to leaves on only the lower half of the plant, a 10-mL spray of either 25 or 50 mg·L-1 of each GA4+7 and BA was enough for complete protection against leaf chlorosis. Increasing volumes had no additional benefit on leaf chlorosis, but increased the chances of unwanted stem elongation.
Yao-Chien Chang, Karen Grace-Martin, and William B. Miller
Upper leaf necrosis (ULN) on Lilium `Star Gazer' is a calcium deficiency disorder. In this study, we evaluated the efficacy of foliar Ca sprays and bulb Ca dipping on reducing ULN. Necrosis severity of a single leaf was determined by an index from 0 (healthy) to 5, based on symptom progression and necrosed leaf area. Single leaf severity was then summed for all leaves to yield a whole-plant severity rating. Single daily applications of 25 mm calcium chloride or calcium nitrate sprays for 14 days significantly suppressed the degree of symptom expression; whole-plant severity was reduced from 18 (severely necrosed) to below 3 (essentially unnoticeable). Five single applications at 3.5-day intervals were not effective, even at concentrations up to 150 mm. At concentrations of 100 and 150 mm, 14 daily sprays of calcium chloride or calcium nitrate were toxic and caused leaf tip yellowing; calcium chloride caused more severe phytotoxicity than did calcium nitrate. For effectiveness of foliar Ca sprays, it was necessary to have the Ca solution reach the enclosed, young, expanding leaves. Preplant bulb immersion in calcium chloride was not effective even at concentrations as high as 400 mm for up to 16 hours.
William B. Miller, P. Allen Hammer, and Terri I. Kirk
Commercial greenhouse operators are increasingly using “negative DIF” temperature regimes for crop height control. A negative DIF exists where the night temperature (NT) is greater than day temperature (DT). Large differences in DT-NT strongly suppress stem elongation in many crops, and have been used to reduce labor and material costs for chemical growth regulator applications on Easter lily. We have explored some of the biochemical effects of negative DIF temperature regimes. 'Nellie White Easter lilies were grown (1989 and 1991) at Purdue under a +10 or -10 DIF regime with temperatures adjusted so that daily averages were equal. Plants were harvested at visible bud (VB) and anthesis. Carbohydrates in stems, leaves and flowers were analyzed by HPLC With both temperature regimes, timing data indicated equal daily temperature averages were achieved. Negative DIF severely reduced stem length, and leaf and stem dry weight. Negative DIF reduced leaf and stem total soluble carbohydrate (TSC) content 39-46% at VB and anthesis, while flower TSC was reduced 10-13%. These results indicate negative DIFs have potentially detrimental biochemical effects on Easter lilies. Other techniques, such as early morning temperature drops, were not a part of this study, and their physiological effects should be evaluated as well.
N.K. Damayanthi Ranwala, Anil P. Ranwala, and William B. Miller
One of the problems associated with preplant bulb dips into plant growth regulator (PGR) solutions is the lack of knowledge of solution efficacy as an increasing number of bulbs are treated. We evaluated the effectiveness (“longevity”) of paclobutrazol (Bonzi) and uniconazole (Sumagic) solutions repeatedly used to dip hybrid lily (Lilium sp.) bulbs. Experiments were conducted over a 2-year period, using sequential 1-minute dips into paclobutrazol (100 or 200 mg·L–1) or uniconazole (2.5 mg·L–1). No difference in plant height occurred as the number of bulbs dipped into PGR solutions increased to at least 55 bulbs per liter. This was true whether bulbs were washed (with tap water to remove soil particles attached to the bulbs) or unwashed prior to the PGR dip. These findings have an important impact on cost effectiveness of bulb dips, as the more times the solution can be used, the lower the cost. Washed bulbs were taller than unwashed bulbs due to lower PGR liquid uptake in washed bulbs (about 1 mL less per bulb) compared to the unwashed bulbs. These results indicate that the hydration condition of bulbs prior to dipping can affect the amount of PGR liquid uptake and therefore final plant height.
Judy Lee, Miguel I. Gómez, and William B. Miller
Plant growth regulators (PGRs) are effective tools for controlling potted plant growth. In this article, the effects of flurprimidol, paclobutrazol, and ethephon media drenches on stem elongation of star of bethlehem (Ornithogalum thyrsoides and Ornithogalum dubium) were investigated. At the lowest paclobutrazol (0.5 mg/pot) and flurprimidol rates (0.05 mg/pot) tested, plant height was reduced 20% to 35% compared with controls in all tested cultivars. Ethephon applied as a media drench when plants reached visible bud (VB) stage had no effect on plant height or flowering. A consumer preference survey of ‘Fire Star’ star of bethlehem (O. dubium) plant height showed that about 60% of participants preferred PGR-regulated plants. With every level of preference increase for shorter plants (on a scale of 1 to 5), participants were willing to pay $0.48 more for the shorter plant.
William B. Miller, P. Allen Hammer, and Terri I. Kirk
Commercial greenhouse operators are increasingly using “negative DIF” temperature regimes to control crop height. A negative DIF exists when greenhouse night temperature is greater than the day temperature. Large negative differences in day and night temperatures strongly suppress stem elongation in many crops. We have explored the effects of negative DIF temperature regimes on leaf, flower, and stem carbohydrate levels in Lilium longiflorum Thunb. `Nellie White'. During two growing seasons, `Nellie White' plants were grown under positive or negative DIF regimes (±5 or 8C) under prevailing daylengths, with temperatures adjusted so that daily temperature averages were equal between regimes. Plants were harvested ≈10 days after visible bud stage and at anthesis. Carbohydrates in stems, leaves, and flowers were analyzed by high-performance liquid chromatography. Compared to plants grown under positive DIF, negative DIF plants showed significantly reduced stem length and leaf and stem dry weights. Negative DIF regimes reduced leaf and stem total soluble carbohydrate (TSC) content by 39% to 46% at visible bud and anthesis, while flower TSC content was reduced by 10% to 13%.
Jeff S. Kuehny, William B. Miller, and Dennis R. Decoteau
Rooted cuttings of Ligustrum japonicum Thunb., an episodically growing species, were grown hydroponically in a controlled-environment growth chamber to determine allocation of glucose, mannitol, total soluble sugars, and total protein in mature leaves, flush leaves, stems, and roots. During the 65 days of episodic growth, 43% of the total soluble sugars was glucose and 33% mannitol. Glucose concentrations of mature leaves decreased during the first root growth episode, increased in almost all plant tissue during a shoot growth episode and decreased in all plant tissue at initiation of a second root growth episode. Mannitol concentrations in the roots and stems decreased during episodes of root growth and increased during a shoot growth episode when leaf flush mannitol concentrations increased. Radiolabeled C applied to leaves before the initiation of the first period of shoot elongation was translocated to the roots. After shoot elongation, just before a root growth episode, most labeled C was translocated to new shoots and roots. Autoradiographs indicated that subsequent episodes of shoot growth were supported by photosynthate from the previous shoot flush. Protein concentrations decreased in all plant tissues during shoot growth but increased in roots and mature leaves during root growth. Concentrations of 15N in leaf and stem tissue indicated retranslocated N supported each episode of shoot growth. Changes in endogenous C and N concentrations and allocation patterns in ligustrum were linked to the control of episodic shoot and root growth.