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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.

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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.

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Polyxeni M. Filios and William B. Miller

We conducted a series of studies to determine the efficacy of a sprayable formulation of 1-methylcyclopropene (1-MCP; AFxRD-038) to inhibit ethylene-mediated flower abscission in Impatiens walleriana. Exposing Impatiens plants to 1.0 μL·L−1 ethylene for 18 hours caused complete abscission of open flowers and most buds. Sprays of the novel 1-MCP formulation at concentrations >2.5 mg·L−1 protected plants from ethylene. At 5 and 10 mg·L−1, the efficacy of 1-MCP increased as spray volume increased from 102 mL·m−2 to 306 mL·m−2. 1-MCP was rainfast with no decrease in efficacy resulting from heavy overhead irrigation within 1–2 minutes of application. Prepared 1-MCP solutions (10 mg·L−1) remained effective up to 2 weeks after mixing if held in airtight containers. The sprayable 1-MCP formulation provided protection against exogenous ethylene for a maximum of 4 days and reduced stress-related abscission from 3 days of darkness (in the absence of exogenous ethylene) at 20 °C or 40 hours darkness at 28 °C.

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Joseph P. Albano, William B. Miller, and Mary C. Halbrooks

A specific physiological disorder, bronze speckle (J.P.A.'s nomenclature), was consistently induced in `First Lady' and `Voyager' marigold with Fe-DTPA concentrations greater than 0.018 mm Fe-DTPA (1 ppm) applied to a soilless medium. The disorder was characterized by specific symptomology distinguished visually by speckled patterns of chlorosis and necrosis, and downward curling and cupping of leaves. The percentage of total leaf dry weight affected with symptoms generally increased with increasing Fe-DTPA treatments. Symptomatic leaf tissue had a greater Fe concentration than corresponding asymptomatic leaf tissue. Leaf Mn concentrations in symptomatic and asymptomatic tissue were similar. In `First Lady', older leaf tissue accumulated more total Fe and was associated with more severe symptoms than younger tissue. Media leachate Fe concentrations increased over 6 weeks and were larger at greater Fe-DTPA treatments. Adjustment of nutrient solution pH to 4.0, 5.25, or 6.5 did not alter media pH, nor did it prevent disorder symptoms. Application of Fe-DTPA containing nutrient solution to a soilless medium resulted in leachate Fe levels 3 times greater than for FeSO4 treatments. Chemical names used: ferric diethylenetriaminepentaacetic acid, monosodium salt (Fe-DTPA).

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Anil P. Ranwala, Garry Legnani, Mary Reitmeier, Barbara B. Stewart, and William B. Miller

We evaluated preplant bulb dips in three commercial plant growth retardants [ancymidol (A-Rest), paclobutrazol (Bonzi), and uniconazole (Sumagic)] for height control in seven oriental hybrid lily (Lilium) cultivars (Aubade, Berlin, Casa Blanca, Muscadet, Sissi, Star Gazer, and Tom Pouce), and seven LA-hybrid lily [hybrids resulting from crosses between easter lily (Lilium longiflorum) and Asiatic hybrids] cultivars (Aladdin's Dazzle, Best Seller, Cebeco Dazzle, Royal Dream, Royal Parade, Royal Perfume, and Salmon Classic) grown in containers. A 1-min dip into a range of concentrations of each product was used to determine the optimum concentrations for height control. The results indicate that bulb dips, especially with uniconazole and paclobutrazol, can be a highly effective means of height control in hybrid lilies. Cultivars varied in their response to growth retardant treatments. In general, LA-hybrid lilies were much more responsive to the growth retardant treatments than oriental hybrids and required lower rates for comparable height control. Delays in flowering, increased bud abortion and leaf yellowing were observed only with high concentrations of uniconazole or paclobutrazol where the height reduction was also too excessive for a commercially acceptable crop.

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Christopher B. Cerveny, William B. Miller, Thomas Björkman, and Neil S. Mattson

The published literature is inconsistent with recommendations for hydrating Ranunculus asiaticus (L.) dried tuberous roots, a common practice in commercial production systems for this ornamental geophyte. Imbibition rate increased with hydration temperature but to lower equilibrium moisture content than when hydrated at cooler temperatures. In the greenhouse, survival was predicted to be greatest when tubers were hydrated at 20 °C. Plant height, visual quality, and foliar dry weight followed a similar trend 4 weeks after planting. These results demonstrate that a hydration temperature between 15 and 25 °C is required to obtain good quality when growing R. asiaticus from its dried tuberous roots.

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Shawn D. Lyons, William B. Miller, H. Christian Wien, and Neil S. Mattson

When grown in containers, pineapple lily (Eucomis sp.) can produce excessively long foliage and tall scapes, particularly in cultivars with tall pineapple lily (Eucomis comosa) parentage. Height control, through the use of plant growth regulators (PGRs), is necessary to improve crop quality of potted pineapple lily. In year 1 of these trials, bulbs of cultivars Reuben, Tugela Jade, and Tugela Gem were given substrate drenches of flurprimidol or paclobutrazol, each at 2, 4, or 6 mg per 6-inch pot. Drenches were applied at the “visible inflorescence” stage. As concentration increased, scapes were generally shorter in all cultivars for both PGRs, but there was no effect on foliage length or production time. At the rates tested, the reduction in scape length was insufficient to produce marketable plants of the three cultivars. In the second year, substrate drenches were applied at an earlier stage than in year 1, at “leaf whorl emergence,” when shoots were about 7 cm tall. The PGR treatments were notably more effective at controlling plant height in the second year. As concentration increased, scape and foliage length was reduced relative to the controls in all three cultivars for both PGRs. For all cultivars, inflorescence leaning and toppling were sharply reduced at all application rates compared with untreated controls. The reduction in plant height observed in year 2, particularly in plants treated with 4 or 6 mg/pot, resulted in plants with compact scapes and foliage proportional with their 6-inch containers.

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Ricardo Campos, Ma. Estela Peralta, Daniel W. Bearden, and William B. Miller

Soluble carbohydrate extracts from Antirrhinum majus L. leaves were fractionated by ion exchange chromatography. Putative mannitol was tentatively identified by retention behavior on two high performance liquid chromatography columns. Mannitol was confirmed using 1H and 13C nuclear magnetic resonance (NMR), and by gas chromatography (GC) and mass spectroscopy (MS). The melting point of authentic and putative mannitol, and a 1:1 mix was from 164 to 166°C. Using the EDTA-phloem exudate technique, mannitol was detected in phloem tissue associated with mature flowers, flower buds, and mature leaves, suggesting that mannitol is translocated in Antirrhinum.

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Mary Taylor Haque, Joseph P. Albano, William B. Miller, Ted Whitwell, and Kristy Thomason

Student Teaching and Research Initiative through Volunteer Employment (STRIVE) is an innovative new program developed collaboratively by faculty and students to offer students work experience opportunities in the Dept. of Horticulture while assisting with horticultural needs. The program promotes volunteerism and education while strengthening participating faculty, staff, and students in areas of research, teaching, or public service. STRIVE requires a voluntary commitment of 3 h/week in an area agreed on by participants and their supervisors. Participants are formally acknowledged by the department for their contributions after completing the semester-long program. Students participating thus far have assisted in teaching laboratories, program development, and greenhouse management.

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William B. Miller*, Martijn Verlouw, Susan S. Liou, Holly O. Cirri, Karen Snover-Clift, and Chris Watkins

Ethylene evolution is a consequence of Fusarium infection of tulip bulbs, yet little is known about the bulb-pathogen interactions involved in the induction or time course of ethylene synthesis. The resulting ethylene can affect adjacent, non-infected bulbs, and results in a variety of disorders, most notably flower abortion. Earlier work indicates that cultivars vary in their sensitivity to ethylene, but there are few data on ethylene production by cultivar. In this experiment, we assessed Fusarium-induced ethylene production in 36 tulip cultivars. Bulbs were wounded, inoculated with a liquid Fusarium suspension (isolated from infected bulbs) and held at 25 °C. Control bulbs were wounded, but not inoculated. Ethylene production was monitored by headspace analysis and gas chromatography. Ethylene increased rapidly after a lag phase of at least 8 days, but there were large differences in ethylene production among cultivars. Of the cultivars tested, `Furand' evolved more than 340 μL/kg/fwt/hr (≈250 μL/L/bulb/day) on the 11th day after infection, a rate ≈440-fold greater than in non-inoculated bulbs. Inoculated cultivars producing ethylene at rates exceeding 50 μLL/kg/hr included `Mary Belle', `Libretto', `Nashville', `Yonina', `Friso', and `Prominence'. About 25% of the cultivars produced ethylene at rates >10 μL/kg/hr, and ≈40% of cultivars produced less than this rate on day 11. High-ethylene producing tulips could be stored separately from other cultivars, or be given increased ventilation during storage or transportation. Knowledge of cultivar variation might also be useful in breeding programs. Further questions concerning the specific tissue responsible for ethylene synthesis (bulb, fungus, or both?) also arise.