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Karim M. Farag, Jiwan P. Palta, and Elden J. Stang

The application of ethanol for enhancing effectiveness of ethephon under field conditions on cranberry (Vaccinium macrocarpon Ait.) fruit was tested during three seasons (1986 to 1988). The formulation containing ethephon plus the surfactant Tergitol (0.3% or 0.5%, v/v) and ethanol (2.5%, 5%, or 10%) consistently increased anthocyanin content in the fruit by 28% to 54% over the control. In general, fruit size was not affected by the ethephon treatment containing ethanol and Tergitol. The application of ethephon plus surfactant did not increase the anthocyanin content in the fruit. The presence of ethanol in the ethephon and surfactant mixture, however, consistently enhanced the fruit anthocyanin content by 21% to 40% as compared to ethephon plus surfactant. No adverse effect of various treatments on vine growth or appearance was noticed over the three seasons. Chemical name used: (2-chloroethyl) phosphonic acid (ethephon).

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Rita A. Teutonico, Jiwan P. Palta, and Tom C. Osborn

Identification of the genes involved in freezing tolerance in oilseed Erussica could lead to genetic improvement of winter survival of this crop and other species, as well as provide greater understanding of the basis of cold stress tolerance in plants. We developed a genetic linkage map for B. rapa using restriction fragment length polymorphisms (RFLPs) and identified molecular markers which are linked to genes controlling vernalization requirement and freezing tolerance. We mapped the location of a group of cold-regulated (`cor') genes from Arabidopsis thaliana in this population and determined their association with freezing tolerance and vernalization requirement. We developed genetically fixed, recombinant inbred lines of B. rapa to assay the physiological processes involved in these cold responses. Specifically, we measured the differences in lipid composition of the plasma membranes of acclimated and nonacclimated plants of a subset of this population. We will determine if the genes involved in the physiological responses to cold temperature are also associated with the acquisition of freezing tolerance.

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Yu-Kuang Chen, John B. Bamberg, and Jiwan P. Palta

Tetraploid somatic hybrids between S. tuberosum (tbr) and S. commersonii (cmm) have been produced to incorporate desirable traits such as cold hardiness from cmm into cultivated potatoes. While nonacclimated freezing tolerance (NA) of these somatic hybrids were as low as tbr fusion parent, their acclimation capacity (ACC) approximated that of the parental mean. In order to further explore the potential of using these somatic hybrids in breeding programs and to examine the segregation of genes conferring NA and ACC in somatic hybrids, progenies have been developed from either selfing somatic hybrids or crossing them with a tuberosum breeding line, Wis 231. In total, 48 selfed and 6 backcross progenies were characterized for the expression of NA and ACC. The NA derived from cmm was still poorly recovered in both sets of progenies. However, ACC did show some variation ranging from the level of sensitive fusion parent to that of the selfed parent, HA 26-5. None of the progeny had ACC as high as their cmm parent. Our results suggest that the expression of NA was suppressed by the cold sensitive genome of tbr. Thus, ACC is the form of cold tolerance from cmm, which appears to be most easily accessed though these somatic hybrids.

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Matthew D. Kleinhenz, Christopher C. Gunter, and Jiwan P. Palta

A direct comparison was made of several commercially available calcium sources applied on two different schedules for their effectiveness in increasing tuber medullary and periderm tissue calcium concentrations in 170–284-g tubers of the cultivar Atlantic grown on a Plainfield sandy loam. Plots (6 x 3 m) were arranged in a CR design in 1993 and a RCBD in 1994 (eight replications). Paired measurements of tuber Ca concentration and internal quality (±hollow heart, ±internal brown spot) were made on individual tubers produced in plots with no additional or additional Ca (168 kg Ca/ha) supplied from either gypsum, liquid calcium nitrate, or NHIB. Two Ca and N application schedules were compared: 1) application at emergence and hilling (non-split), 2) application at emergence, hilling, and 4 and 8 weeks after hilling (split). All plots received 224 kg H/ha balanced with ammonium nitrate. In general, tuber yield and grade were unaffected by treatments in 1993 and 1994, but overall percent A-grade was lowest and percent B-grade highest in 1993 compared with 1994 data. In 1993, all treatments receiving Ca had greater mean tuber medullary and periderm tissue Ca concentration values and a greater percentage of tubers with an elevated Ca concentration compared with non-Ca-supplemented controls. The overall incidence of tuber internal defects was 5% in 1993. All split schedule treatments receiving Ca showed 0% internal defects. In contrast, nearly 8% of the tubers from control plots showed some defect. The medullary tissue Ca concentration of 65% of the tubers having either defect was below the median value of Ca concentration for the entire experiment in 1993. Similar evaluations are underway for the 1994 crop. These data suggest that tuber calcium concentration may be related to the incidence of these internal defects.

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Björn H. Karlsson, Jiwan P. Palta, and Peter M. Crump

Our previous research has provided evidence that in-season calcium applications can increase tuber calcium and improve tuber quality with reduced internal defects. To determine if increasing the tuber calcium concentration also mitigates tuber bruise incidence, five commercially relevant potato (Solanum tuberosum L.) cultivars (`Russet Burbank', `Atlantic', `Snowden', `Superior', and `Dark Red Norland') were grown during three seasons, 1999–2001. Three split applications of a calcium/nitrogen water soluble blend totaling 168 kg·ha–1calcium were made starting at hilling. All plots, including controls, received an equal amount of total nitrogen in a season. Tubers were allowed to be bruised during normal machine harvest standard to commercial production in Wisconsin. Over 100 tubers from each replication (5–10 replications/treatment) were cut and examined for the incidences of bruise and internal brown spot. Paired samples of medullary tissue were taken for measuring calcium concentration. As expected, tuber tissue calcium concentration increased significantly, in all cultivars and in all years, with in-season calcium application. Bruise incidence varied among cultivars and seasons. Although tuber calcium concentration varied among seasons, `Atlantic' and 'Snowden' consistently had the lowest calcium concentration, whereas `Superior' and `Dark Red Norland' consistently had the highest calcium concentration. Meta-analysis of pooled data for three years showed that blackspot bruise incidence was significantly reduced with calcium application in `Atlantic', `Burbank', and `Snowden'. On the other hand, `Dark Red Norland' and `Superior' had low incidence of bruise and were unaffected by calcium applications. Regression analyses of pooled data from all cultivars for three years revealed a significant quadratic relationship between blackspot bruise and tuber tissue calcium as well as between blackspot bruise and internal brown spot. A linear to plateau plot of medullary calcium concentration versus blackspot bruise incidence revealed that bruise incidence is minimized between 200 and 250 μg/kg (dry wt)–1 tuber calcium concentration. To our knowledge, ours is the first study providing evidence for reducing bruise by improving tuber calcium. Variations in the bruise incidences among cultivars generally followed tuber calcium concentration suggesting a genetic control. Given the role of calcium in improved membrane health and enhanced wall structure, and as a modulator of physiological responses, it is not surprising that internal brown spot and bruise incidences are reduced by in-season application to calcium-deficient cultivars.

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Beth Ann A. Workmaster, Michael Wisniewski, and Jiwan P. Palta

Infrared video thermography has recently been used to visualize ice nucleation and propagation in plants. At the UW–Madison Biotron facility, we studied the formation of ice in various parts of fruit-bearing cranberry (Vaccinium macrocarpon Ait.) uprights. The fruits were at the blush to red stages of ripening. Samples were nucleated at –1 or –2°C with ice-nucleating-active bacteria (Pseudomonas syringae). Following nucleation, samples were cooled to –6°C in ≈1 hour. The following observations were made: 1) When nucleated at a cut end, ice propagated rapidly throughout the stem and into the leaves at a tissue temperature of about –4°C. However, ice did not propagate from the stem through the pedicel to reach the fruit. During the 1 hour after ice propagation in the stem, the fruit remained supercooled. 2) Within the duration of the experiment, leaves could not be nucleated from the upper surface. Ice from the lower leaf surface did nucleate the leaf, and ice propagated from the leaf to the stem and other leaves readily. 3) Both red and blush berries could only be nucleated at the calyx end of the fruit. 4) Red berries supercooled to colder temperatures and for longer durations than the blush berries. 5) In support of our previous studies, red berries were able to tolerate some ice in their tissue. These observations suggest that: 1) The upper leaf surface and the fruit surface (other than the calyx end) are barriers to ice propagation in the cranberry plant; and 2) at later stages of fruit ripening the pedicel becomes an ice nucleation barrier from the stem to the fruit. This may contribute to the ability of the cranberry fruit to supercool.

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Beth Ann A. Workmaster, Jiwan P. Palta, and Michael Wisniewski

Infrared video thermography was used to study formation of ice in leaves, stems, and fruit of cranberry (Vaccinium macrocarpon Ait. `Stevens'). Ice formed on the plant surface at -1 or -2 °C by freezing of a droplet of water containing ice nucleation-active bacteria (Pseudomonas syringae van Hall). Samples were then cooled to a minimum of -8 °C. Observations on the initiation and propagation of ice were recorded. Leaves froze only when ice was present on the abaxial surface. Once initiated, ice propagated to the stem and then readily to other leaves. In both unripe and ripe fruit, ice propagation from the stem to the fruit via the pedicel was not observed. Fruit remained supercooled for up to 1 hour after ice was present in the stem. Fruit could only be nucleated when ice was present at the calyx (distal) end. Red (ripe) berries supercooled to colder temperatures and for longer durations than blush (unripe) berries before an apparent intrinsic nucleation event occurred. These observations provide evidence that leaves are nucleated by ice penetration via stomata. The ability of fruit to supercool appears to be related to the presence of barriers to extrinsic ice propagation at both the pedicel and fruit surface. Stomata at the calyx end of the fruit in the remnant nectary area may provide avenues for extrinsic ice nucleation.

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Mustafa Özgen, Karim M. Farag, Senay Ozgen, and Jiwan P. Palta

Highly colored cranberries are desired for both fresh and juice markets. Berries accumulate more color when allowed to stay on the vines longer. However, early fall frosts often force growers to harvest before the fruit has reached its optimal color. This is especially true for the berries under the canopy. No product is currently available for grower to accelerate the color development in cranberries. Result from recent studies suggests that a natural lipid, lysophosphatidylethanolamine (LPE), can accelerate color production in fruit and, at the same time, promote shelf life. LPE is a natural lipid and is commercially derived from egg and soy lecithin. The influence of LPE on anthocyanin accumulation and storage quality of cranberry fruit (Vaccinium macrocarpon Ait. `Stevens') was studied. Cranberry plants were sprayed with LPE at about 4 weeks before commercial harvest at multiple locations. Experiments were conducted in 1997, 1998 and 1999. Fruit samples were taken at 2 and 4 weeks after spray application to determine the changes in the fruit color. Plots were wet harvested using a standard commercial method and stored in a commercial cold storage facility. Marketable fruit were evaluated at 1 and 2 months after cold storage to determine effect of LPE on shelf life of cranberries. In general, a preharvest application of LPE resulted in a 9% to 27% increase in fruit anthocyanin concentration compared to the control. LPE treatments also resulted in 8% to 12% increase in marketable fruit compared to the control following cold storage. Influence of LPE on fruit quality was more apparent after 1 month of storage. These results are consistent with the observed effects of LPE on tomatoes. Interestingly ethanol application also enhanced storage quality. Our results suggest that a preharvest application of LPE may have the potential to enhance color and prolong shelf life of cranberry fruit.

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James S. Busse, Senay Ozgen, and Jiwan P. Palta

Shoot tip necrosis has been attributed to calcium deficiency in in vitro cultures, resulting in death of the stem tip, the loss of apical dominance, and axillary branch development. Using an in vitro shoot culture system with Solanum tuberosum L. cv. Dark Red Norland, we studied the development of injury symptoms at the microscopic and tissue levels at a range of media calcium concentrations varying from 6.8 to 3000 μm. Light and electron microscopic studies revealed that the primary injury due to calcium deficiency was the death and collapse of expanding pith cells below the shoot apex. The structure and organization of the shoot apical meristem was the same when plants were cultured on sufficient or suboptimal media calcium concentrations. However, the apical meristem senesced following subapical shoot tissue collapse. Death of the shoot apical meristem was a secondary effect of calcium deficiency, resulting in loss of apical dominance. Studies with 45Ca indicated that calcium was distributed in a gradient along the shoot, with highest concentration at the base and the lowest at the apex. Shoot tip necrosis developed after 20 days of culture on the suboptimal calcium concentration medium. The development of these symptoms and axillary shoot growth was associated with the lack of calcium accumulation in the shoots. Our results provide evidence that a primary injury of calcium deficiency is localized in the expanding pith cells below the shoot apical meristem and this injury results in the collapse of subapical cells. Death of the shoot apical meristem is a secondary injury resulting from calcium deficiency.

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Senay Ozgen, James S. Busse, and Jiwan P. Palta

The important roles of calcium on plant growth and development including cell division and cell elongation is well documented. The purpose of the present study was to determine the impact of root zone calcium on the growth and health of potato apical meristem and on the maintenance of apical dominance. For this purpose, single-node potato cuttings (Solanum tuberosum L. cv. Dark Red Norland) were grown in sterilized modified Murashige and Skoog (MS) media containing varying concentrations of calcium (1 to 3000 μM). After 13 to 30 d of growth, plantlets were harvested and data for height of the main shoot and for the number of axillary shoots produced were recorded. Plantlets were ashed and tissue calcium concentration was determined. Shoot height was retarded with decreasing concentration of calcium in the media. Calcium deficiency induced shoot tip injury and loss of apical dominance. Tip injury was followed by the development of axillary shoots. The number of axillary shoots increased from one to 21 as calcium concentration in the media decreased from 3000 to 1 μM. At calcium concentration of 1500 μM or higher, there was a single main shoot with no axillary shoots. Addition of ethylene glycol tetra acetic acid (EGTA), a calcium chelator, to the media with 2720 μM calcium (sufficient calcium) resulted in the development of shoot injury and in the formation of axillary shoots. Calcium deficiency injury symptoms were prevented by the addition of a calcium analog, strontium, to MS media deficient in calcium. Strontium has been reported to strongly bind to plant cell walls and the inclusion of strontium prevented injury in shoots of plants grown on calcium-deficient media. These results suggest that strontium is able to mimic the role of calcium in the maintenance of cell wall integrity and supports previous studies that showed that calcium deficiency results from cell wall collapse of the subapical cells.