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Mustafa Ozgen, Senay Ozgen, and Jiwan P. Palta

Recent studies from our laboratory have demonstrated that lysophoshatidylethanolamine (LPE) is able to accelerate fruit ripening while at the same time promoting shelf life. LPE is a natural lipid and is commercially extracted from egg yolks and soybeans. We studied the influence of LPE on the pattern of anthocyanin accumulation and storage quality of cranberry fruit (Vaccinium macrocarpon Ait. cultivar Stevens). For this purpose 2 x 2-m plots were established in cranberry beds at two separate locations near Wisconsin Rapids. Experiments were conducted in 1997 and 1998 seasons. Plots were sprayed with LPE (extracted from egg yolk and soybean) 3 to 4 weeks before harvest. Spray solution included 200 ppm LPE, 3% ethanol, and 0.1% detergents (either Tergitol or Sylguard). Fruit samples were taken from a part in the plot periodically to determine the changes in the fruit. The rest of the plots were commercially wet harvested with a machine and stored in cold storage. Marketable fruit were counted at various times of cold storage to determine effect of LPE on shelf life of cranberries. In general, application of LPE from both sources resulted in 20% to 35 % increase in fruit anthocyanin contents. Also LPE treatment resulted in 10% to 20% increase in marketable fruit in cold storage. A postharvest dip of cranberry fruit with 50 ppm LPE solution for 15 min also resulted in about a 20% to 30% increase in marketable berries during cold storage. The results of this study shows that pre- and postharvest applications of LPE can add value to cranberry crop including better and more uniform colored fruit, enhance self life, and earlier harvest.

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Senay Ozgen, Mustafa Ozgen, and Jiwan P. Palta

Several recent studies, including from our laboratory, have provided evidence that by improving tuber calcium level, we can improve tuber quality such as low internal defects and better storability. The purpose of this study was to be determine the influence of supplemental calcium fertilization on tuber size and tuber number. For this purpose, plantlets of Solanum tuberosum cv. Russet Burbank raised in tissue culture were planted in 20-L pots filled with sandy loam soil with pH of 6.9 and soil calcium level of 350 ppm. All treatments received same total amount of nitrogen (at the rate of 280 kg·ha–1). Five treatments were evaluated: i) nonsplit nitrogen (from ammonium nitrate), ii) split nitrogen (from ammonium nitrate), iii) split nitrogen + gypsum, iv) split nitrogen (from liquid nitrogen) + calcium chloride, and v) split nitrogen (from calcium nitrate). The total calcium was applied at the rate of 168 kg·ha–1. Gypsum application was made at 4 weeks after planting, and other sources of calcium were applied on a split schedule (equally split at 4, 6, 8 weeks after planting). Four months after planting, tubers were harvested and evaluated. In general, all calcium treatments had lower tuber number and greater tuber size compared to the nonsplit nitrogen control. The percentage of total A-grade tubers as well as the percentage yield from A-grade tubers was increased by all calcium applications. These results suggest that calcium content I the soil can influence both potato tuber number and tuber size.

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Mustafa Özgen, Sookhee Park, and Jiwan P. Palta

Mitigation of ethylene promoted leaf senescence by lysophosphatidylethanolamine (LPE) was studied. Micropropagated `Russet Burbank' potato (Solanum tuberosum L.,) plantlets were grown on MS media in sterile culture tubes. After 2 weeks of growth, tubes were sealed and ethylene gas was applied to obtain 5 nL·L–1 final concentration in the culture tubes. Observations and measurements were taken two weeks after ethylene injection. Potato plantlets treated with ethylene showed severe leaf senescence symptoms such as epinasty, lack of growth, yellowing and axillary shoot formation. These observations indicate that apical dominance has been lost with ethylene treatment. The same experiment was repeated with different concentrations of LPE in the MS medium. Inclusion of 50 or 100 mg·L–1 of LPE in the medium mitigated the damage normally caused by applied ethylene. Leaves of plantlets exposed simultaneously to LPE and ethylene had significantly higher chlorophyll content and more healthy leaves compared to plantlets grown on medium lacking LPE. Results of this study suggest that LPE may have the potential to retard ethylene-promoted leaf senescence and may mitigate ethylene induced loss in apical dominance of micropropagated potato plantlets.

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Beth Ann A. Workmaster and Jiwan P. Palta

Little is known about the growth and development of the cranberry plant (Vaccinium macrocarpon Ait.) in response to air and soil temperatures in the spring. During this period, marked changes in cranberry bud hardiness are known to occur (from –20 to 0 °C), with the greatest changes occuring before bud elongation. The ability to predict changes in bud phenology and hardiness in relation to thermal time would be useful to growers in making frost management decisions. To establish a working growth model, canopy air and soil temperatures were continuously recorded in 1996, 1997, and 1998 in a cranberry bed (cv. Stevens) in central Wisconsin. In spring, samples of uprights were randomly collected from several locations within the bed and sorted according to a nine stage bud classification from tight bud to bloom. Controlled freezing tests were performed on uprights from the most advanced stages present that constituted 10% or more of a sample on a given date. Heat units were calculated from hourly canopy air temperatures. Despite the varied weather conditions over the3 years, a distinct relationship existed between the accumulation of heat units and the advancement of the crop. Spring 1998 was very early and resulted in the accumulation of more heat units before initial and advanced bud swell was observed compared to the other 2 years. Initial evaluation suggests that soil temperatures between 5 to 10 °C and photoperiod may play a role in modulating the effect of air temperatures. Further refinement of this model and the predictive value for frost hardiness changes will be discussed.

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Karim M. Farag and Jiwan P. Palta

We have demonstrated that postharvest treatment of McIntosh apple fruits with Lysophosphatidylethanolamine (LPE) delays the loss of firmness. In the present study, McIntosh apples were preharvest treated by hand spray to the run off point. Fruits were sprayed on August 28, 1991 and harvested two weeks later. One half of the tree was sprayed with LPE (100 ppm) and the other half was the control. Three trees were used in this study. Periodical samples for starch test, internal CO2 and ethylene, total soluble solids and evolved CO2 and ethylene were taken to monitor the progress of ripening. At harvest, on average, LPE treated apples abscised 26% while the control trees abscised 55%. LPE treated apples colored earlier and had more uniform and intense color than the control. In a related study, we have found the LPE can delay senescence of tomato leaf and fruit tissues. The delay of the abscission of apples by LPE, found in the present study, might be due to the effect of LPE on delaying senescence of cells in abscission zone of apple fruit pedicle. These results suggest that LPE has the potential to substitute for the use of NAA on apples before harvest and at the same time LPE can improve color uniformity and density of McIntosh apples.

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Zienab F.R. Ahmed and Jiwan P. Palta

Banana is one of the most consumed tropical fruits around the world. It is marketed nearly all year-around and has a relatively short shelf life. Fruits are harvested mature green and treated with ethylene to stimulate ripening before distribution and sale. The fruits generally ripen within 4–5 days after ethylene treatment and sold primarily at yellow stage of ripening. After turning yellow the fruit becomes unsuitable for marketing in 1–3 days. Thus 1–2 days of improvement in the fruit shelf life could enhance the market value of banana. Previous studies conducted in our laboratory have demonstrated that both pre- and postharvest application of lysophosphatidylethanolamine (LPE) can retard aging and improve shelf life of various fruits. The objective of this study was to investigate the possibility of improving shelf life of banana fruit by a postharvest dip in LPE. For this purpose, whole fruits obtained from the market at ripeness stage of 2.5 (about 75% green) were dipped in solution of 500 ppm LPE for 30 minutes and observed for a period of five days at room temperature. Each treatment was applied to 50 uniform fruits. From each hand bought, an equal number of fruits were separated for LPE and control treatments to reduce the variability. Five days after dip treatment, the fruit treated with LPE were firmer and thicker as compared with the control. Starch breakdown was also delayed in the LPE-treated fruits. LPE treatment slowed the development of brown spots on the peel tissue. Both peel and pulp tissue of LPE-treated fruits had lower ion leakage compared with the control. Fruit peel slices treated with LPE for 3 hours also showed a decrease in ion leakage and respiration rate at 24 hours after treatment. Results of the present study indicate that a postharvest dip treatment with LPE may improve shelf life of banana fruit by 1–2 days. These results suggest that LPE may improve shelf life by maintaining membrane integrity, reducing respiration, and slowing the breakdown of starch and cell walls during ripening and senescence of banana fruit tissue.

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Christopher C. Gunter and Jiwan P. Palta

Tuber tissue calcium has been linked to several potato quality characteristics, including internal defects and the susceptibility of tubers to decay by soft rotting Erwinia species. We were particularly interested in studying the relationship between supplemental calcium fertilization during the seed tuber production cycle to raise the seed piece calcium concentration and the impact on crop performance the following season. The role of seed tuber tissue calcium level on seed piece decay, growth, development, and performance of the plant was evaluated for cultivars Russet Burbank, Dark Red Norland, Atlantic, Superior, and Snowden. This study was performed over four growing seasons. Seed tubers were raised with varying calcium and the following season, individual tubers (over 3,000 total for 4 years of study) were sampled for calcium and hand planted in the field. They were evaluated for seed piece decay and total tuber yield during the growing season. Seed tubers raised with supplemental calcium resulted in significantly higher mean calcium content than the control tubers. In general, calcium-raised seed tubers tended to produce a more vigorous main sprout and higher tuber yield. We also found that there are significant differences among these cultivars for the characteristics measured. Consistently, in all three years, `Atlantic' responded to test conditions with the lowest decay values, and `Dark Red Norland' consistently showed the highest decay values. This suggests that there may be a genetic component involved in these two responses and these genotypic differences could be exploited to improve cultivated potatoes.

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Sandra E. Vega and Jiwan P. Palta

Previous studies in our laboratory both in pine needles and potato leaves have shown evidence of an increase in 18: 2 (linoleate) in the purified plasma membrane fraction during cold acclimation. This increase was reversible on deacclimation, thereby suggesting a link between the accumulation of 18: 2 and acquisition of freezing tolerance. These studies suggest that the activity of specific desaturases may be modulated during cold acclimation. This study was aimed at studying the possible involvement of stearoyl-ACP desaturase (delta9) in potato cold acclimation response. Our approach was to study the induction of delta9 desaturase at the transcript level by using potato delta9 desaturase gene specific primers and reverse transcriptase. For this purpose, mRNA from S. tuberosum (cold sensitive, unable to acclimate) and S. commersonii (cold tolerant, able to cold acclimate) was extracted before and after acclimation. Sequence analysis confirmed that the amplified band was delta9 desaturase. Our results show that there is an increase in delta9 desaturase gene transcripts during cold acclimation and that this increase is associated with the cold acclimation response in potato. These results together with previous reports on the increase in 18: 2 in the plasma membrane during cold acclimation give more evidence toward the involvement of stearoyl-ACP desaturase (delta9) in the potato cold response.

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Ahmed A. Tawfik and Jiwan P. Palta

The optimum temperature regime for Solanum tuberosum cv. Russet Burbank is usually 20/15°C day/night. We studied the impact of heat stress (30/25°C, day/night) on the growth of this heat sensitive cultivar under controlled conditions (UW-Biotron). Plants were grown in sandy-loam soil which tested at 1500 Kg/ha Ca. Plants were at the maximum temperature for 6h during the middle of the day with a photoperiod of 14 hrs. All pots received identical amounts of total N (rate: 225 Kg N ha1.). The treatments were: (1) NSN: non-split N (N application 1/2 emergence, 1/2 two wks later): (2) SPN: split-N (1/2 emergence 1/6 at 2, 5 and 8 wks later); (3) SPN+Ca: Split-N+Ca (Ca at 2, 5 and 8 wks after emergence, total Ca from CaNO3 was 113 Kg ha1). Total leaf FWT and DWT was significantly reduced in NS treatment by heat stress at 13 wks as compared to optimum conditions. However, this was not reduced in SPN and SPN+Ca. Under heat stress: (a) SPN + Ca gave the highest leaf FWT and DWT, stomatal conductance, transpiration rate, and leaflet tissue Ca content; (b) Young expanding leaflets gave higher growth rate with SPN and SPN + Ca than NSN; (c) Ca content of mature leaflet decreased progressively in both NSN and SPN but not in SPN + Ca. Our results show that application of Ca and N during heat stress can mitigate stress effects and that maintenance of a certain level of calcium in leaf tissue is important under heat stress.

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Bjorn H. Karlsson and Jiwan P. Palta*

Supplemental calcium application has been shown in our previous work to improve tuber quality and reduce internal defects. We evaluated the response under field conditions of five commerically significant cultivars to a combination of calcium nitrate, calcium chloride and urea (168 kg·ha-1 per season) over three seasons. We were able to determine that the cultivar with the greatest response to supplemental calcium for reduced bruising, `Atlantic' had the lowest levels of tuber tissue calcium. Conversely, cultivars with least response to supplemental calcium, `Dark Red Norland' and `Superior', had the highest levels of tuber tissue calcium. `Snowden' was both intermediate in response to calcium and tuber tissue concentration. Based on data for 3 years, we determined that across cultivars the calcium concentration at which tubers no longer respond is ≈250 ppm and ranges for individual years from 195 to 242 ppm. These results suggest that seasonal variation for individual cultivars may affect the tuber need for calcium for reduced bruising. Although the exact mechanism is not known, we believe that calcium supplemented to bulking tubers may lead to improved cell membrane stability, increased wall structure or enhanced ability of tubers to repair following injury. The results of our study show that supplemental calcium fertilization has the ability to significantly reduce the incidence of tuber bruising for several cultivars.