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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.

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Beth Ann A. Workmaster and Jiwan P. Palta

Recent work in our laboratory has shown that pre- and postharvest applications of lysophosphotidylethanolamine (LPE) retard senescence processes in several fruit and flower species (apple, tomato, carnation). Banana was selected to develop a rapid bioassay to test the effects of LPE and other substances on various processes associated with senescence. Excised peel pieces from fully yellow `Grand Nain' bananas (Musa AAA) were incubated in petri dishes containing LPE solution (0, 25, 50, and 100 ppm) for 4 days. Fresh weight and ethylene production was measured daily. At the end of the experiment, tissue density, ion leakage, and soluble protein leakage was measured. Ion and soluble protein leakage was significantly lowered with 100 LPE. The 100 ppm LPE also significantly inhibited ethylene production after only 2 hours of treatment and this low level was maintained during the experiment. Peel tissue from the 100 ppm LPE remained firm and intact while tissue from the other treatments expanded and lost integrity. By day 2, peel from the 0, 25, and 50 ppm LPE gained significantly in fresh weight, while tissue treated with 100 ppm initially lost and then only slightly gained in fresh weight. Our results suggest that LPE is able to protect membrane function in senescence. Furthermore, these results provide evidence that LPE may also be retarding senescence by modulating the ethylene pathway.

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Karim M. Farag and Jiwan P. Palta

A natural lipid, lysophosphatidylethanolamine (LPE), was used as a tomato fruit ripening agent. The effect of this compound on hastening the ripening and on the defoliation of the `Heinz 7155' processing tomato and the Glamour fresh-market tomato (Lycopersicon esculentum Mill.) was compared to the effect of ethephon. Vines were sprayed to runoff in the field with a hand sprayer and fruits were harvested 2 weeks or 20 days later in a single harvest operation. LPE (100 mg liter-1) accelerated ripening of both processing and fresh-market tomatoes without defoliation. LPE-treated tomatoes had a better shelf life than the control or ethephon-treated fruit, whether they were harvested at the breaker, pink, or red stage of maturity. The combination of LPE and ethephon (100 mg liter-1) enhanced tomato ripening without damaging the foliage, suggesting that LPE can mitigate the undesirable effects of ethephon on foliage and the fruit. The LPE-related lipid phosphatidyldimethylethanol-amine dipalmitoyl (PDED) also was able to enhance some aspects of keeping quality of tomato fruits, but was not able to enhance fruit ripening. Phosphatidylethanolamine was not as effective as LPE or PDED. It appears that the active molecule of this natural lipid is the lyso form. Our results provide evidence that LPE can enhance tomato fruit ripening and postharvest storage life of vine-ripe fruits and fruits picked at early ripeness stages.

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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 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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Beth Ann A. Workmaster and Jiwan P. Palta

`Stevens' cranberry (Vaccinium macrocarpon Ait.) terminal bud freezing stress resistance was assessed by nonlinear regression utilizing relative scoring of the post-thaw bud growth and development based on defined bud stages 2 weeks following controlled freezing tests. Bud stages tested were chosen based on a phenology profile from each sampling date throughout the spring season. Previous year (overwintering) leaf freezing stress resistance was evaluated after both 2 days (injury) and 2 weeks (survival). The Gompertz function with a bootstrapping method was used to estimate the tissues' relative freezing stress resistance as the LT50. Bud injury levels (LT50) were expressed as the temperatures at which the mean potential regrowth capability was impaired by 50%, as compared with the unfrozen controls. In leaves, the LT50 is the temperature at which 50% injury (2-day evaluation) or survival (2-week evaluation) was modeled to occur. Dramatic changes in terminal bud relative freezing stress resistance occurred both within and between the tight and swollen bud stages. These results clearly show that seasonal changes in freezing stress resistance do not necessarily parallel changes in crop phenology and bud development. These results indicate that some physiological, biochemical, or fine anatomical changes may explain the seasonal loss in hardiness within a visual bud stage. Previous year leaves may possess the ability to recover from freeze-induced injury, as leaf survival was found to be the most reliable indicator of cranberry leaf hardiness. Major shifts in phenology and bud and leaf hardiness coincided with the rise of minimum canopy-level air temperatures to above freezing. The nonlinear regression technique utilized made it possible to estimate LT50 with data points comprising half or more of the sigmoidal dose response curve. Our study provides precise and quantitative estimates of the cold hardiness changes in cranberry terminal buds and leaves in spring. From precise estimates we were able to define critical temperatures for the impairment of cranberry bud growth. This is the first systematic study of cranberry terminal bud cold hardiness and spring bud development in relation to changes in the soil and air temperatures under natural conditions. Our study shows that regrowth assessment of the cranberry upright inherently describes the composite effects of freezing stress on plant health.

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

Pathogenic bacteria (Erwinia spp.) can have a significant impact on stand establishment and sprout health. These bacteria cause soft rot of the seed piece, which is common in wet spring conditions resulting in great economic loss. Recent studies have demonstrated that the incidence and severity of soft rot can be significantly reduced by increasing tuber calcium. We investigated the influence of seed piece calcium on tuber production. Field growing potato plants were treated with supplemental calcium during tuber bulking (calcium at 168 kg·ha–1 from calcium nitrate or N-Hib) to increase the seed tuber medullary calcium levels. All three cultivars (`Superior', `Atlantic', `Dark Red Norland') responded to supplemental calcium application with increases in mean calcium contents, even though soil tests showed high native calcium levels (1000 kg·ha–1). Seed tubers were sampled for calcium by removing a longitudinal slice from the center of each tuber and planting one of the resulting halves for seed piece decay evaluation and the other for yield evaluation. Calcium nitrate-treated seed tubers produced higher yields compared to ammonium nitrate and N-Hib in `Atlantic' in `Dark Red Norland'. This trend did not hold true for `Superior'. Our results suggest that a) it is possible to increase seed piece tuber calcium levels with supplemental calcium application even in soils testing high in calcium and b) improving the calcium concentration of the seed piece can increase tuber yield in some cultivars.