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- Author or Editor: William R. Miller x
Interactions of ethephon and irradiance reduction were investigated in terms of flower bud blasting in Easter lily (Lilium longiflorum Thunb. `Nellie White'). Silver thiosulfate (STS) was investigated as an inhibitor of ethylene-induced bud abortion. Fourteen days of 92% irradiance reduction significantly increased bud abortion when plants were exposed to 2.1 mm ethephon. Bud abortion was 39% and 60% for plants grown in ambient and reduced irradiance, respectively. Silver thiosulfate was applied to plants 2 or 3 weeks after the date of the first visible bud, followed by ethephon treatment 2 days later. Bud abortion was significantly reduced by 1 or 2 mm STS, without phytotoxicity. Pretreatment with 1 or 2 mm STS as early as 4 weeks before ethephon exposure significantly reduced ethephon-induced bud abortion. Silver thiosulfate application could inexpensively reduce flower bud abortion during latter stages of greenhouse forcing of Easter lilies.
Fruits of rabbiteye blueberries (Vaccinium ashei Read cvs. Climax and Woodard) harvested by hand in 1984 and machine in 1985 were stored in air, 100% N2, and in 10%, 15%, or 20% CO2 with 5% O2. Storage of either blueberry cultivars in high-CO2 atmospheres resulted in greater percentages of marketable and firm fruit, and better sensory ratings, than did storage in air. Fruit of ‘Climax’ lost less weight, were firmer, and developed less decay after 21 or 42 days of storage than ‘Woodard’ fruit. Fruit quality characteristics of hand-harvested ‘Climax’ stored for 42 days and machine-harvested ‘Climax’ stored for 21 days in 20% CO2 with 5% O2 were similar to those of freshly harvested fruit.
A reputation for coarse root systems with dominant taproots, and for slow shoot development among seedlings, limits use of hickory species (Carya Nutt.) that could increase diversity in managed landscapes. We examined effects of root pruning and application of auxin on root and shoot development of seedlings of several species of hickory. Our hypothesis was that pruning the radicle shortly after seed germination and subsequent treatment with auxin would increase root branching without curtailing development of the shoot. Germinated seeds of Carya aquatica (F. Michx.) Nutt., Carya cordiformis (Wangenh.) K. Koch, Carya laciniosa (F. Michx.) Loudon, Carya ovata (Mill.) K. Koch, and Carya tomentosa (Lam.) Nutt. were treated by removing two-thirds of the length of the radicle with and without immediate application of 3000 mg·L−1 indole-3-butyric acid (IBA) via Hormex rooting powder #3 to the remaining one-third of radicle. Neither treatment altered stem height, stem caliper, or root dry weight. After 75 days, root-pruned seedlings of Carya ovata without auxin had 42% fewer fibrous first-order lateral roots than did unpruned controls. Root pruning plus auxin led to a 79% increase in the number of fibrous first-order lateral roots of C. laciniosa and an ≈50% increase in the shoot dry weight of C. aquatica. Both root pruning and root pruning plus auxin evoked formation of taproot branches for all species. Because species differed in responses of root and shoot systems to root pruning with and without auxin, the practice should be implemented cautiously based on the species.
`Marsh' white grapefruit (Citrus paradisi Macf.) harvested from exterior canopy positions were less tolerant of 0.5 or 1.0 kGy irradiation than were interior fruit. Irradiation at 0.0, 0.5, or 1.0 kGy resulted in 0.0%, 24.3%, and 37.5% surface pitting of fruit, respectively. Pitting was reduced 30% by temperature conditioning with vapor heat at 38 or 42 °C for 2 hours. Exterior canopy fruit had ≈2-fold more pitting, had greater weight loss, and were firmer than interior canopy fruit. Fruit weight loss increased and firmness decreased as conditioning temperature and irradiation dose increased. Total soluble solids, titratable acidity, and flavor decreased with increasing irradiation dose. The peel of exterior canopy grapefruit was damaged more by irradiation than was that of interior fruit, but irradiation damage was reduced by temperature conditioning.
The feasibility of utilizing different patterns of air temperature changes over the light and dark periods was investigated to provide a basis for greenhouse energy conservation. ‘Grand Rapids’ lettuce was grown hydroponically in microprocessor controlled growth chambers, under a light level of 325 µmol s-1m-2 PPF. Air temperatures were: a) increased from 15° to 35°C (late-peak), b) decreased from 35° to 15° (early-peak), and c) increased to 35°, then back to 25° (mid-peak) during the 16-hr light period. The late and mid-peak patterns had a gradual decrease in night air temperature, whereas the early peak pattern had a gradual increase in night air temperature. Each of these patterns averaged 25° during the light period, and 20° during the dark period. “Early-peak” plants grew poorly, whereas plants grown under the mid- and late-peak regimes grew well. Early morning diffusive resistance was similar for early- and mid-peak plants. Transpiration rates followed the air temperature changes.
The fungicides thiabendazole (TBZ) or imazalil were applied at 1 g·liter-1 at 24 or 53C to `Marsh' and `Redblush' grapefruit (Citrus paradis i Macf.) to reduce fruit susceptibility to chilling injury (CI) and decay. There was more CI and decay on `Marsh' grapefruit than on `Redblush'. CI was found to be lower in grapefruit that had been dipped at 53C than at 24C. CI was higher after water dips without fungicide. Imazalil was found to be more effective in reducing CI than TBZ. Fungicides reduced decay at both temperatures, and imazalil was better than TBZ. Results of this study confirm the benefits of high-temperature fungicide treatments for maintaining grapefruit quality and indicate some benefits of high-temperature fungicide treatments for reducing CI.
Individually plastic-film-wrapped or waxed ‘Marsh’ grapefruit (Citrus paradisi Macf.) were conditioned (34.5°C, 3 days) at low (30% ± 5% RH) or high (95% ± 5% RH) humidity before cold storage (10° ± 1°; 90% ± 5% RH). Predisposition to storage decay by conditioning was investigated by examining fruit inoculated with penicillium spores either before or after conditioning. Penicillium rot in fruit that was inoculated after conditioning was reduced in plastic-film-wrapped fruit (37%) relative to waxed fruit (74%) only after 2 weeks at 10° ± 1° + 1 week at 21° ± 1° storage. Of the fruit inoculated prior to conditioning, the incidence of decay was lower in fruit conditioned at high RH than in fruit not conditioned or conditioned at low RH. No coating effect of wax or plastic-film was observed. Fruit quality tended to be adversely affected by conditioning, but this effect became less obvious with storage. Fruit coated with plastic film had a better general appearance than waxed grapefruit.
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.
Boltonia asteroides L. `Snowbank' (Snowbank boltonia), Eupatorium rugosum L. (eastern white snakeroot), and Rudbeckia triloba L. (three-lobed coneflower) were subjected to drought for 2, 4, and 6 days during the fall and spring. Leaf gas exchange, leaf water potential, growth, and carbohydrate partitioning were measured during drought and throughout the following growing season. Leaf gas exchange of B. asteroides was not affected by drought treatment in the fall, not until day 6 of spring drought, and there were no long-term effects on growth. Transpiration and stomatal conductance of R. triloba decreased when substrate moisture decreased to 21% after drought treatment during both seasons. Assimilation of drought-treated R. triloba decreased when substrate moisture content decreased to 12% during spring but was not affected by drought in the fall. There was a decrease in the root-to-shoot ratio of R. triloba that had been treated for 4 days, which was attributed to an increase in the shoot dry weight (DW) of treated plants. Reductions in spring growth of E. rugosum were observed only after fall drought of 6 days, and there were no differences in final DWs of plants subjected to any of the drought durations. Spring drought had no effect on growth index or DW of any of the perennials. Boltonia asteroides and R. triloba had increases in low-molecular-weight sugars on day 4 of drought, but E. rugosum did not have an increase in sugars of low molecular weight until day 6 of drought. Differences in drought response of B. asteroides, E. rugosum, and R. triloba were attributed to differences in water use rates.
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.