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Sorkel Kadir

High temperature adversely affects photosynthetic rates and thylakoid activities in many species, but photosynthesis response to heat stress is not well defined in grapes (Vitis L.). Genotypes within species respond differently to high temperatures, indicating a genetic variability for the trait. The objective of this study was to determine the physiological responses of two grape species to high temperature, at the whole-plant level and at the cellular level. Gas exchange, relative chlorophyll content, and chlorophyll fluorescence of intact leaves and thermostability of extracted thylakoids of the American (V. aestivalis Michx.) `Cynthiana' and European (V. vinifera L.) `Semillon', `Pinot Noir', `Chardonnay', and `Cabernet Sauvignon' wine grapes were evaluated. One-year-old vines were placed in controlled environmental chamber held at 20/15, 30/25, or 40/35 °C day/night for 4 weeks. Net CO2 assimilation (A) rate, stomatal conductance (gs), transpiration (E) rate, chlorophyll content, and chlorophyll fluorescence of intact leaves were measured at weekly intervals. Chlorophyll fluorescence of thylakoids extracted from V. aestivalis `Cynthiana' and V. vinifera `Pinot Noir' subjected to temperatures ranging from 20 to 50 °C was measured. Optimal temperatures for photosynthesis were 20/15 °C for `Cynthiana' and `Semillon' and 30/25 °C for the other three V. vinifera cultivars. The A, gs, E, chlorophyll content, and chlorophyll fluorescence values at 40/35 °C were lower in `Cynthiana' than `Pinot Noir'. In general, reduction of A coincided with decline in gs in `Cynthiana', whereas no strong relationship between A and gs was observed in V. vinifera cultivars. Variable chlorophyll fluorescence (Fv) and the quantum efficiency of photosystem II (Fv/Fm) of intact leaves for all the cultivars decreased at 40/35 °C, with severe decline in `Cynthiana' and `Cabernet Sauvignon,' moderate decline in `Semillon' and `Chardonnay', and slight decline in `Pinot Noir'. A distinct effect of high temperature on Fv and Fv/Fm of `Cynthiana' was exerted after 2 weeks of exposure. Prolonged-exposure to 40/35 °C led to 78% decrease in Fv/Fm in `Cynthiana', compared with 8% decrease in `Pinot Noir'. In general, Fv and Fv/Fm of extracted thylakoids declined as temperature increased, with more decline in `Cynthiana' than in `Pinot Noir'. Based on A rates and Fv/Fm ratios, results showed that `Cynthiana' has lower optimal temperature for photosynthesis (20/15 °C) than `Pinot Noir' (30/25 °C). Chlorophyll fluorescence responses of intact leaves and extracted thylakoids to high temperatures indicate that `Pinot Noir' possess higher photosynthetic activity than `Cynthiana'. Results of this work could be used in selection programs for the development of heat resistant cultivars in the warmest regions.

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Sorkel Kadir* and Edward Carey

High tunnel strawberry (Fragaria × ananassa) production experiment was conducted in south central Kansas, which consisted of two cultivars and four tunnels. The same experimental design was conducted under field conditions. The objectives of this study were to compare strawberry production and quality under high tunnels to those grown in the field and to assess the potential for high tunnels for early-season strawberry production. Plug plants of `Sweet Charlie' and `Chandler' were planted October 18. Plants were spaced at 12” × 12 “in double rows on raised beds covered with black plastic mulch. Protected plants under high tunnels had 100% winter survival rate compared to 60% of the field plants. Yield and berry quality of the high tunnel plants were by far better than those of field grown plants. Plant growth under high tunnels was about three to four fold higher than the unprotected field plants. `Sweet Charlie' flowered in early February and produced berries one week earlier than `Chandler'. Both cultivars were harvest from early April through late May at weekly interval. `Sweet Charlie' in early April produced an average berry weight of 14 g, soluble solids of 8 °Brix, and the largest average berry weight was 15 g. `Chandler' harvested late April produced larger berries than `Sweet Charlie' with the largest average berry weight of 35 g compared to 31 g for `Sweet Charlie'. In mid May, `Chandler' produced 72% higher yield than `Sweet Charlie'. High tunnel not only produced higher yield and better quality berries than field strawberries but it has a potential to produce early crop and extend the season production of strawberry in Kansas.

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Sorkel Kadir and Robert Wample

Evaluation of thermostability of photosynthetic apparatus of intact leaves and isolated thylakoids of five cultivars of wine grapes (Vitis vinifera) was conducted. Four- week- old plants of Semillon, Chenin Blnac, Pinot Noir, Chardonnay, and White Riesling, were placed into a control environment chamber held at 20/15° 30/25°, and 40/35 °C day/night temperature for 14 days. Induced (F0), variable (Fv), and maximum fluorescence (Fm) and the quantum yield of net photosynthesis (Fv/Fm) were measured after 1-14 days exposure. All fluorescence parameters were not affected by 20/15° and 30/25°C. However, high temperature (40/35°C) increased F0 and decreased Fm, Fv, and Fv/Fm. These changes were severe in Semillon and Chenin Blanc, moderate in Chardonnay and White Riesling and scarce in Pinot Noir. Average high temperature data that are experienced in Yakima Valley area will be presented. Isolated thylakoid membranes from the cultivars were heated at 20-40°C. and uncoupled electron transport was determined. Thylakoid stability to heating varied similarly to whole-plant response to high temperature.

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Said Ennahli and Sorkel Kadir

Variability due to soil types, topography, and climate within a vineyard influences grapevine physiological parameters and fruit quality. Technical feasibility of using precision Geographic Information System (GIS) as a viticulture tool to improve vineyard management and increase wine quality will be investigated. The study was conducted in an experimental vineyard where rows consist of plots with 24 cultivars and selections randomly planted and managed similarly. Monitored vineyard parameters collected by Global Positioning System (GPS) location include soil characteristics, soil moisture, vine growth, crop load, and fruit characteristics. Geospatial maps are used to differentiate yield between the cultivars and selections as high, medium, or low. Production was determined from each variety/selection within the vineyard. Yield parameters were number of clusters, cluster weight, and weight of 50 berries; fruit composition (such as pH), titratable acidity, soluble solids concentration, and anthocyanins were measured. Maps for each factor will be derived via GIS tools and spatial analysis will be conducted to assess which spatial variability factor has more effect on grapevine physiology, yield, and fruit quality. This type of analysis can be used by grape growers to achieve specific wine characteristics in a large or small vineyard by controlling all sources of variability, leading to the ability to perform precision viticulture in the future, with low cost.

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Said Ennahli and Sorkel Kadir

Partial root-zone drying (PRD) irrigation management has been developed for grapevines as an efficient method to control excessive growth, improve fruit quality, and save water without compromising yield. PRD is based on knowledge of the mechanisms that control transpiration and requires slow dehydration of half of the plant root system, whereas the other half is irrigated. A study was conducted in the field to evaluate the effect of PRD on physiological characteristics, growth, yield, and fruit quality of three grape cultivars. The wetting and drying cycle of the PRD-vine root system is alternated on a 10–14 day schedule. Significant reduction in vigor was observed in treated plants compared with control plants. Root biomass was not affected, but fine roots significantly increased in PRD-treated plants, compared with that of the control. This contributed to the ability of PRD-treated plants to maintain leaf water potential similar to that of the control. Stomatal conductance of PRD plants was significantly reduced when compared with that of the control plants. Abscisic acid (ABA) concentration in leaves of PRD vines increased significantly when compared to the control vines. PRD treatment significantly increased yield and fruit quality when compared with the control treatment. PRD significantly increased water use efficiency (pruning weight per unit of water applied). This study shows that PRD stimulated ABA production in the drying roots, which caused reduction in stomatal conductance and transpiration rate, leading to a substantial reduction in vegetative growth without compromising yield and fruit quality.

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Sorkel Kadir and Kassim Al-Khatib

Soil residual herbicides registered for use on grapes can be applied from fall to spring, before weed emergence. However, ample early-spring moisture and warm weather may enhance weed emergence before herbicide application in the spring and prevent timely application. Therefore, fall application of herbicides can be beneficial if herbicides would provide adequate weed control in the following spring. Warm and wet winters may enhance herbicide degradation and shorten herbicide residual activity that result in poor weed control the following spring. Fall and spring application of oryzalin or norflurazon applied alone or in combination with diuron, simazine, or oxyfluorfen were evaluated for weed control in commercial vineyards at Oskaloosa and Eudora in northeast Kansas in 2003 and 2004. Weeds were not controlled adequately with oryzalin or norflurazon applied alone. At the end of the growing season, however, weed control was greater with spring than fall application. In addition, weed control with norflurazon was slightly greater than oryzalin. Norflurazon or oryzalin applied in combination with simazine, diuron, or oxyfluorfen controlled more weeds than norflurazon or oryzalin applied alone. The greatest control was with norflurazon or oryzalin applied with oxyfluorfen. In general, all herbicide combinations applied in the spring and fall provided similar weed control 4 months after spring application. However, at the end of the growing season, weed control was 10% to 20% greater when herbicides applied in the spring than fall. This study showed that acceptable weed control can be achieved when norflurazon or oryzalin is applied with oxyfluorfen and diuron in the fall.

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Sorkel Kadir, Edward Carey, and Said Ennahli

Plant growth, yield, and fruit quality of two strawberries (Fragaria ×ananassa Duch.)—`Chandler' and `Sweet Charlie'—grown under high tunnels (HTs) were compared with that of field plants during 2002–03 and 2003–04 growing seasons. Plug plants were planted in mid-October 2002 and mid-September 2003 on raised beds covered with black polyethylene mulch. Microclimate of the HTs protected strawberry crowns from winter damage and advanced fruit production 5 weeks earlier than that of plants grown under field conditions. From December to February, average minimum and maximum crown temperatures under the HTs were 5 and 12 °C warmer than those of the field crowns, respectively. The earliest HT fruit were harvested on 7 Apr. 2003 and 11 Mar. 2004. Yield and fruit quality under the HTs were superior to that of field-grown plants. HT plants, especially `Sweet Charlie', bloomed earlier than did field plants, but `Chandler' produced higher yield than `Sweet Charlie' late in the season. Larger fruit with higher soluble solids concentration (SSC) were produced inside the HTs than outside. HT `Sweet Charlie' fruit were sweeter than `Chandler' fruit, but `Chandler' produced larger fruit. Larger leaf area, greater number of leaves and shoot biomass, more branch-crowns, and fewer runners were developed under HTs than field conditions. Total leaf area, leaf production, total shoot biomass, and number of branch-crowns of HT `Chandler' were greater than HT `Sweet Charlie'. Results of this study indicate that strawberry plants under HTs were not only precocious, but also produced higher yields and superior quality to that of field plants. HT conditions suppressed runner growth, but enhanced branch-crown development.

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Sorkel A. Kadir and Edward L. Proebsting

In Dec. 1990, sweet cherry (Prunus avium L.) selections varied in floral bud kill from 9% to 92% following exposure to severe cold. In the following winter, the hardiness of two hardy and two tender selections was analyzed by differential thermal analysis (DTA) to screen selections for hardiness. In a mild winter, when buds remained at their minimum hardiness level, the hardy selections consistently were > 2C hardier than the tender selections. About one-half of that hardiness difference was associated with differences in tissue water content, the other half with unknown factors. Buds of the tender selections began to develop earlier and bloomed earlier than the hardy selections. DTA analysis of floral bud populations separated selections that clearly differed in floral bud hardiness.

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Sorkel A. Kadir and Ed L. Proebsting

Differential thermal analysis (DTA) was used to measure deep supercooling in flower buds of Prunus dulcis Mill., P. armeniaca L., P. davidiana (Carr.) Franch, P. persica (L.) Batsch, three sweet cherry (P. avium L.) selections, and `Bing' cherries (P. avium L.) during Winter 1990-91 and 1991-92. Low temperatures in Dec. 1990 killed many flower buds. After the freeze, dead flower primordia continued to produce low-temperature exotherms (LTEs) at temperatures near those of living primordia for >2 weeks. In Feb. 1992, cherry buds that had been killed by cooling to -33C again produced LTEs when refrozen the next day. As buds swelled, the median LTE (LTE50) of dead buds increased relative to that of living buds, and the number of dead buds that produced LTEs decreased. LTE artifacts from dead flower priimordia must be recognized when DTA is used to estimate LTE50 of field-collected samples.

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Sorkel Kadir, Gaganpreet Sidhu, and Kassim Al-Khatib

Thermotolerance of photosynthesis and productivity in `Chandler' and `Sweet Charlie' strawberry plants (Fragaria ×ananassa Duch.) exposed to three temperature regimes was studied. Net CO2 assimilation rate (A), variable chlorophyll fluorescence (Fv), efficiency of photosystem II (Fv/Fm), relative chlorophyll content, plant growth, and fruit yield and quality were measured. High temperature (40 °C day/35 °C night) was more detrimental to photosynthesis and productivity than the moderate or low temperature (30/25 or 20/15 °C). Net CO2 assimilation rate in both cultivars was markedly reduced by 40/35 °C, although there was slight decline in `Sweet Charlie' at 30/25 °C. `Chandler' maintained significantly higher A rates than `Sweet Charlie' for at least three weeks of heat stress, indicating that `Chandler' might tolerate longer exposure to high temperature. In parallel to the decrease in A rate, intercellular CO2 concentration (Ci) and instantaneous water use efficiency (WUE) were significantly decreased at high temperature. `Chandler' leaves were cooler and transpired more than `Sweet Charlie' leaves, suggesting that each cultivar adopted different heat resistance mechanisms at 40/35 °C. There were changes in Fv and Fv/Fm with increasing temperature, indicating irreversible damage to photosystem II at 40/35 °C might have occurred. The trend of reduction in stomatal conductance (g S) in both cultivars at high temperature did not coincide with the reduction in A rates. Decline in A rates at high temperature was more related to changes in Fv/Fm than to g S activity. The optimal temperature for vegetative growth was 30/25 °C. Reduction in A rate at high temperature resulted in reduction in total leaf area (LA), shoot, root, and leaf biomasses. Strawberry roots were more responsive than shoot growth to temperatures above 20/15 °C. Fruit yield for `Chandler' was higher at 20/15 °C than at 30/25 °C, suggesting that `Chandler' might have a higher source-to-sink relationship at 20/15 °C than at 30/25 °C. Fruit skin color was temperature dependent only for `Chandler'. A quadratic relationship between flower development and duration of exposure to 30/25 °C for both cultivars was observed; more than two weeks of 30/25 °C can be detrimental to flower development. Regardless of the cultivar and duration of exposure, 40/35 °C was the temperature regime most detrimental to fruit set.