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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).

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Laurie S. Weiss, John B. Bamberg, and Jiwan P. Palta

Solanum acaule (acl) and Solanum commersonii (cmm) represent the extremes of frost tolerance and cold acclimation ability among potato species. We have combined these species with cultivated S. tuberosum (tbr) to develop a potato with desired tuber traits and a high degree of frost tolerance. For this purpose diploid cmm was made 4x and crossed with naturally 4x acl. The F1 and F2 appear to exhibit hybrid vigor for vine growth for flowering, but none had frost tolerance greater than the parents. The F1 and F2 were crossed with S. tuberosum ssp. andigena and Katahdin via 2n eggs resulting in 6x 3-way hybrids. These hybrids were evaluated both in the field and laboratory for frost tolerance and acclimation ability. Results showed an increase of 1°C of frost tolerance and 2°C increase in cold acclimation capacity in the hybrids as compared to the sensitive tbr parents. Some of the 6x (3-way) hybrids produced significant tubers but yield and earliness needs much improvement. These results demonstrate that it should be possible to move both non acclimated freezing tolerance and cold acclimation ability from wild to cultivated species and offer exciting opportunities to enhance potato production in frost prone areas in the world.

Supported by USDA/NRI grant 91-3700-6636 to J.P.P. and J.B.B..

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J. Angel Saavedra, Elden J. Stang, and Jiwan P. Palta

Uniconazole (UCZ) can control tree size by suppressing tree growth. Growth control of one year-old `Haralred' on MAC 9 `MARK' (dwarf) and EMLA 7 (semidwarf) rootstock was evaluated in the greenhouse. Uniconazole (65 or 130 mg/L) was sprayed 0, 1, 2 or 3 times at 3 week intervals. Total shoot growth was inhibited 31% and 24% on `MARK' and EMLA 7 rootstock, respectively, with 130 mg/L. Rootstock and scion diameter and number of leaves per tree were not affected by UCZ. Total leaf area on `MARK' rootstock increased when UCZ was applied once at 65 or 130 mg/L. On EMLA 7 two 130 mg/L sprays resulted in 22% less total leaf area compared to the control. UCZ applied three times reduced specific leaf weight on EMLA 7 trees 12% compared to the control. Branch angle was increased proportional to UCZ applications on semidwarf rootstock from 40° to 47°, and decreased on dwarf rootstock from 47° to 39°. Stomatal conductance increased 43% on `MARK' with 130 mg/L UCZ applied two times. Net photosynthesis of attached leaves did not differ. All UCZ treatments produced 18 to 56% fewer total flower clusters per tree than the control. UCZ appeared to delay bloom significantly.

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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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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, Jiwan P. Palta, Christopher C. Gunter, and Keith A. Kelling

Three Ca sources and two application schedules were compared for their effectiveness for increasing tissue Ca concentrations in 170 to 284 g field-grown tubers of `Atlantic' potato (Solanum tuberosum L.). Additional observations were made of internal physiological defects. Paired measures of tissue (periderm and nonperiderm) Ca concentration and internal quality (±hollow heart, ±internal brown spot) were made on individual tubers produced in plots fertilized with N at 224 kg·ha-1 and Ca at either 0 or 168 kg·ha-1, supplied from either gypsum, calcium nitrate or NHIB (9N-0P-0K-11Ca, a commercial formulation of urea and CaCl2). Application of N and Ca at emergence and hilling (nonsplit) was compared to application at emergence, hilling, and 4 and 8 weeks after hilling (split). Tuber yield and grade were unaffected by treatments. Split Ca application (from either calcium nitrate or NHIB) increased mean tuber nonperiderm tissue Ca concentrations and the percentage of tubers with an elevated Ca concentration in both years compared with non-Ca-supplemented controls. Split Ca application also resulted in greater increases in Ca in nonperiderm tissue than nonsplit Ca application in 1994. Although the correlation coefficient between Ca level in periderm and nonperiderm tissue of >400 individual tubers was highly significant in both study years, linear regression analyses suggested the Ca level in the two tissues were poorly related. Split application was associated with a 37% reduction in the incidence of internal tuber defects, relative to nonsplit application in 1994. Calcium application did not affect tuber internal quality based on means analysis, but chi-square analysis suggested that Ca concentration and internal quality of individual tubers may be related. The incidence of internal defects was 16.4% in tubers with nonperiderm tissue Ca >100 μg·g-1 dry weight compared to 10.6% in tubers with nonperiderm tissue Ca >100 μg·g-1 dry weight. These data suggest that 1) it is feasible to increase tuber Ca levels by field applications of moderate amounts of Ca, 2) tuber quality is impacted by N and Ca application schedule, and 3) Ca concentrations in tuber periderm and nonperiderm tissues may be controlled independently.

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Juan M. Quintana, Helen C. Harrison, James Nienhuis, and Jiwan P. Palta

We have previously observed significant variation for pod Ca concentration among snap bean genotypes. In the present experiment, we compare pod Ca concentration between snap bean and dry bean genotypes. Eight snap bean cultivars and eight dry bean cultivars were chosen to be evaluated for pod Ca concentration in summers of 1995 and 1996 at Hancock, Wis. The experimental design consisted in randomized complete blocks with three replications in 1995 and six in 1996. Snap and dry beans were planted in June and hand-harvested in August for both experiments. Soil analysis showed 430 ppm of Ca in soil at time of planting. No additional Ca was applied. Plots consisted of 10 plants each. Harvesting was made by collecting a pooled sample of medium size pods from the 10 plants. Ca determinations were made using an atomic absorption spectrophotometer. Data was presented as mg of Ca per gram of dry weight, pooled from both years, and analyzed using SAS. Results reflected significant differences between genotypes. Checkmate (5.5) showed the highest pod calcium concentrations and Labrador (3.9) the lowest among snap beans. G0122 (5.1) resulted in the highest and Porrillo (3.6) the lowest within dry beans Results were consistent across years. Snap beans (4.6) presented significantly higher pod calcium concentration than dry beans (4.2). Apparently, snap bean genotypes have the ability to absorb calcium from the soil more efficiently than dry bean genotypes, and this phenomenon is not significantly influenced by environmental factors.

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Juan M. Quintana, Helen C. Harrison, James Nienhuis, Jiwan P. Palta, and Michael A. Grusak

To assess nutritional potential, pod yield, and Ca concentration of pods and foliage were determined for a snap bean population, which included sixty S1 families plus four commercial varieties. The experimental design was an 8 × 8 double lattice, repeated at two locations (Arlington and Hancock, Wis.). Snap beans were planted in June 1993 and machine harvested in August 1993. Calcium analyses were made using an atomic absorption spectrophotometer. Significant differences were detected in pod Ca concentration and yield among the S1 families. Pod size and Ca concentration were inversely correlated (R 2 = 0.88). Distinct differences between the locations were not observed, and higher Ca genotypes remained high regardless of location or pod size. Low correlation (R 2 = 0.21) between pod and leaf Ca concentration was found. Pods of certain genotypes appeared to have the ability to import Ca more efficiently than others, but this factor was not related to yield.