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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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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.

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

The objective of this study was to determine effects of bulb size on production time and factors influencing crop quality in pineapple lily (Eucomis sp.) cultivars developed originally for cut flower production. The percentage of bulbs producing an inflorescence increased as bulb size increased. One hundred percent of bulbs >18 cm circumference flowered in three of the four cultivars whereas ‘Tugela Jade’ exhibited 88% flowering. The number of flowers per inflorescence increased as bulb size increased. Scape length increased as bulb size increased in ‘Reuben’. Inflorescence length increased as bulb size increased in ‘Reuben’, ‘Tugela Jade’, and ‘Tugela Gem’. Days to anthesis from planting decreased as bulb size increased in ‘Reuben’ and ‘Tugela Jade’. For all cultivars, the largest bulbs produced the greatest number of leaves per plant and the highest quality inflorescences, largely attributable to the larger number of flowers produced per inflorescence compared with smaller bulbs.

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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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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.

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William B. Miller, Anil P. Ranwala, Garry Legnani, Merel Langens-Gerrits, Geert-Jan de Klerk, Johannes Eckelmann, and Michael Ernst

Ornamental geophytes comprise a large and diverse group of plants characterized by underground storage organs that serve the obvious function of reserve storage and subsequent supply during early stages of shoot growth. Relative to many agronomic and horticultural crops, the fundamental physiological bases of carbon metabolism, partitioning, and utilization in geophytes are unclear. One reason is diversity in organ morphology (bulb, corm, tuber, root, rhizome, etc.), storage carbohydrate (starch, fructan, glucomannan, etc.), and growth habit (e.g., synanthous vs. hysteranthous flowering). Knowledge of factors that control accumulation and mobilization of carbohydrate reserves may lead to manipulations that considerably improve the quality and culture of these crops. We are utilizing a variety of techniques and experimental systems to study selected internal and external controls or influences on geophyte carbohydrate metabolism and partitioning. Specific examples to be discussed include bulb storage temperature effects on starch and fructan metabolism in Tulipa, effects of carbon source and dormancy breaking treatments on starch and glucomannan metabolism in in vitro-grown Lilium bulblets, photoperiod control of fructan accumulation in Dahlia seedlings, and biochemical and molecular features of soluble and wall-bound invertases in developing Lilium longiflorum flower buds.

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William B. Miller, Neil S. Mattson, Xiaorong Xie, Danghui Xu, Christopher J. Currey, Kasey L. Clemens, Roberto G. Lopez, Michael Olrich, and Erik S. Runkle

Ethephon [(2-chloroethyl) phosphonic acid] is a plant growth regulator that releases ethylene on application and can abort flowers, stimulate branching, and inhibit stem elongation. Although ethephon is used as a foliar spray during the commercial production of many ornamental crops, its effectiveness as a drench has not been widely investigated. We performed experiments to quantify the effects of an ethephon drench on growth and flowering of a range of bedding plant and Narcissus cultivars and to assess the effect of lime on ethylene release from a peat substrate. A substrate drench of 0, 100, 250, or 500 mg·L−1 ethephon was applied to 12 potted Narcissus cultivars at one location, and up to 200 mg·L−1 was applied to 24 cultivars of bedding plants at three locations. Compared with untreated controls, ethephon generally reduced plant height at flowering and the effect increased with increased concentration. For example, Narcissus treated with a 250 mg·L−1 ethephon drench had stems that were 20% to 40% shorter at the end of flowering than control plants. However, ethephon drenches generally caused a 2- to 3-day flowering delay, and two cultivars had a phytotoxic response. Among the bedding plants studied, a 100-mg·L−1 ethephon drench suppressed plant height at flowering by greater than 30% in Catharanthus, Celosia, Dianthus, and Verbena, but by only 10% to 15% in Lobelia, Lycopersicon, and Tagetes. The drenches also delayed flowering in 10 of the 16 crops measured and decreased dry mass accumulation in all of the crops measured. Ethephon release from peat substrate became maximal ≈120 h after application and was dramatically increased by incorporation of dolomitic lime up to a rate of 9.5 kg lime per m3 of peat. Collectively, these studies show that ethephon substrate drenches inhibit stem elongation in a broad range of floriculture crops, but can also delay flowering and reduce biomass accumulation.