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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, 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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Sandra E. Vega-Semorile, John B. Bamberg, and Jiwan P. Palta

Frost damage to the foliage is a common problem where potatoes are grown, and results in significant reductions in tuber yield. Frost injury also limits the cultivation of high-yielding S. tuberosum cultivars in the mountain regions of Central and South America, where potato is a staple crop. Recent studies have shown that some wild potato species possess a high degree of non-acclimated frost tolerance (growing in normal conditions) as well as high cold acclimation capacity (able to increase frost tolerance upon exposure to cold). Natural frosts affecting potatoes are of two types: a) late spring or early fall frost, where the minimum temperature during the frost episode can be very low; b) frost during the growing season, where the minimum temperature during the frost episode is not as low. It is expected that potato species able to acclimate rapidly would survive better from the latter type of frosts, whereas species having higher acclimation capacity might have a great chance to survive better from the former type of frosts. The objective of this study was to find out if there is genetic variability for the speed of acclimation among different tuber-bearing wild potato species. The species used were: S. acaule, S. commersonii, S. megistacrolobum, S. multidissectum, S. polytrichon, S. sanctae-rosae, and S. toralapanum. Relative freezing tolerance of these species was measured during cold acclimation. Preliminary results suggest that there are differences in the speed of acclimation among these species. We found that these species can be divided into four groups: i) non-acclimators; ii) rapid acclimators, with low to medium acclimation capacity; iii) slow acclimators, with low to medium acclimation capacity; iv) slow acclimators, with high acclimation capacity. We plan to use this information in our breeding program aimed at improving the freezing tolerance of potatoes.

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Sandra E. Vega, Jiwan P. Palta, and John B. Bamberg

Two major components of frost resistance are freezing tolerance in the nonacclimated state (growing in normal condition) and capacity to cold acclimate (increase in freezing tolerance upon exposure to chilling temperatures). In addition to these two major components, numerous factors contribute to frost survival. Although the rate of cold acclimation and deacclimation have been recognized as important factors contributing to frost survival, very little information about them is available. Our objective was to determine if there is variability in the rate of cold acclimation and deacclimation among tuber-bearing wild potato species: S. acaule Bitter, S. commersonii Dunal, S. megistacrolobum Bitter, S. multidissectum Hawkes, S. polytrichon Rydb., S. sanctae-rosae Hawkes, and S. megistacrolobum subsp. toralapanum (Cárdenas & Hawkes) Giannattasio&Spooner. Relative freezing tolerance of these species was measured after 0, 3, 6, 9 and 12 days of cold acclimation and after 12 and 24 hours deacclimation. Our results showed there were differences in the rates of cold acclimation and deacclimation among these species. With respect to the rate of acclimation we found these species can be divided into four groups: (i) early; (ii) late acclimators; (iii) progressive acclimators, and (iv) nonacclimators. Likewise, a wide range of cold deacclimation behavior was found. Some species showed as low a loss of 20% of their freezing tolerance, others showed as much as >60% loss after 12 hours of deacclimation. Significant deacclimation was observed in all cold acclimating species after 1 day. These results demonstrate that the rates of cold acclimation and deacclimation were not necessarily related to the cold acclimation capacity of a species. Rapid acclimation in response to low temperatures preceding a frost episode and slow deacclimation in response to unseasonably warm daytime temperatures could be advantageous for plants to survive frost events. Thus, in addition to nonacclimated freezing tolerance and acclimation capacity, it would be very desirable to be able to select for rapid acclimation and slow deacclimation abilities. Results demonstrate that variability for these two traits exists in Solanum L. (potato) species.

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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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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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Mustafa Ozgen, Jiwan P. Palta, and Stephen B. Ryu

Ethephon [2-(chloroethyl) phoshonic acid] is used widely to maximize the yield of ripe tomato fruits. However, ethephon causes rapid and extensive defoliation, overripening, and promotes sunscald damage to the fruit. Recent studies from our laboratory have provided evidence that lysophosphatidylethanolamine (LPE) can reduce leaf senescence. We investigated the potential use of LPE to reduce damaging effect of ethephon on tomato foliage and influence on the activity of phospholipase D (PLD). Disruption of membrane integrity has been suggested as a primary cause of senescence in plants. PLD is known to be a key enzyme, which initiates the selective degradation of membrane phospholipids in senescing tissues. Two-month-old tomato plants (`Mountain Spring') grown in greenhouse condition were sprayed with water, 200 ppm LPE, and 1000 ppm ethephon. In addition, LPE spray prior to ethephon or mixture with ethephon were also tested. Leaves were sampled after 0, 2, 5, 24, 72, and 168 h of spray application, for PLD activity measurements. Spray of LPE prior to ethephon spray or inclusion of LPE in the ethephon spray reduced foliar injury by ethephon. Activity of soluble PLD was increased dramatically in leaves sprayed with ethephon initially and than dropped by 7 days. We also found that LPE-treated leaves had lower PLD activity than the ethephon-treated leaves. Plants treated with LPE-ethephon mixture also showed significantly lower PLD activity. These results suggest that LPE treatments mitigate ethephon injury to tomato plants. Furthermore, it appears that this mitigation involves modulation of the activity of PLD.

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Sandra E Vega, Jiwan P. Palta, and John B. Bamberg

Frost injury limits the cultivation of potatoes in many regions around the world. We are currently studying the factors that contribute to frost survival in potato in an attempt to improve its frost tolerance. Wild potato species have been distinguished for their high degree of non-acclimated frost tolerance (growing under normal conditions) and their high cold acclimation capacity (able to increase frost tolerance upon exposure to cold). Cold acclimation can be reversed upon exposure to warm temperatures (deacclimation). The ability to gain freezing tolerance rapidly in response to low temperatures as well as not being able to deacclimate rapidly in response to warm daytime temperatures would be advantageous for a plant against spring or fall freezes. Last year we presented evidence for the variability in the speed of cold acclimation among 7 wild tuber-bearing potato species (S. acaule, S. commersonii, S. megistacrolobum, S. multidissectum, S. polytrichon, S. sanctae-rosae and S. toralapanum). The same set of species was used for the present study to find out if there is also variability for the speed of deacclimation. Relative freezing tolerance of these species was measured before and after cold acclimation as well as after one day of deacclimation (exposure to warm temperatures). Our results suggest that there are differences in the speed of deacclimation among these species. We found that while some species lost near a half of their hardiness, others lost only a third or less of their hardiness after one day of deacclimation.

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Beth Ann A. Workmaster, Jiwan P. Palta, and Jonathan D. Smith

In Wisconsin, the cranberry plant (Vaccinium macrocarpon Ait.) is protected from freezing temperatures by flooding and sprinkle irrigation. Due to the high value of the crop, growers typically overprotect by taking action at relatively warm temperatures. Our goal is to provide recommendations for improved frost protection strategies by studying seasonal hardiness changes in different parts of the cranberry plant (leaves, stems, buds, flowers, fruit). Stages of bud growth were defined and utilized in the hardiness determinations. Samples were collected from mid-April to mid-Oct. 1996 and cuttings were subjected to a series of freezing temperatures in a circulating glycol bath. Damage to plant parts was assessed by visual scoring and observation, ion leakage, and evaluation of the capability to regrow. The following results were obtained: 1) Overwintering structures, such as leaves, stems, and buds, can survive temperatures <–18°C in early spring, and then deacclimate to hardinesses between 0 and –2°C by late spring. 2) In the terminal bud floral meristems are much more sensitive to freeze–thaw stress than are the vegetative meristems. 3) Deacclimation of various plant parts occurred within 1 week, when minimum canopy temperatures were above 0°C, and when the most numerous bud stage collected stayed the same (bud swell). 4) Fruits >75% blush can survive temperatures of –5°C for short durations. By collecting environmental data from the same location we are attempting to relate plant development, frost hardiness, and canopy temperatures (heat units).