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Gene A. Giacomelli and William J. Roberts

The diversity of coverings for the greenhouse and other plant production structures has increased dramatically during the past 4 decades. This has resulted from the availability of new types of covering materials and enhancements of previously existing materials, as well as the demands for technological improvements within the expanding controlled environment agricultural industry. The types of coverings currently available are dominated by plastics. These range from traditional glass to the recent advent of polymer plastics, such as thin films or multilayer rigid thermoset plastic panels. Available enhancements such as ultraviolet radiation (UV) degradation inhibitors, infrared radiation (IR) absorbency, and anti-condensation drip surfaces, as well as their physical and spectral properties are discussed. The selection of specific covering alternatives has implications for the greenhouse superstructure and its enclosed crop production system.

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William R. Graves, Robert J. Joly, and Michael N. Dana

Honey locust (Gleditsia triacanthos var. inermis Wind.) and tree-of-heaven Ailanthus altissima (Mill.) Swingle] sometimes are exposed to high root-zone temperatures in urban microclimates. The objective of this study was to test the hypothesis that seedlings of these species differ in how elevated root-zone temperature affects growth, leaf water relations, and root hydraulic properties. Shoot extension, leaf area, root: shoot ratio, and root and shoot dry weights were less for tree-of-heaven grown with the root zone at 34C than for those with root zones at 24C. Tree-of-heaven with roots at 34C had a lower mean transpiration rate (E) than those grown at 24C, but leaf water potential (ψ1) was similar at both temperatures. In contrast, shoot extension of seedlings of honey locust grown with roots at 34C was greater than honey locust at 24C, E was similar at both temperatures, and ψ1 was reduced at 34C. Hydraulic properties of root systems grown at both temperatures were determined during exposure to pressure in solution held at 24 or 34C. For each species at both solution temperatures, water flux through root systems (Jv) grown at 34C was less than for roots grown at 24C. Roots of tree-of-heaven grown at 34C had lower hydraulic conductivity coefficients (Lp) than those grown at 24C, but Lp of roots of honey locust grown at the two temperatures was similar.

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Kanogwan Kerdnaimongkol, Anju Bhatia, Robert J. Joly, and William R. Woodson

Diurnal variation in the chilling sensitivity of `Rutgers' tomato (Lycopersicon esculentum Mill.) seedlings was examined. Chilling sensitivity was highest in seedlings chilled at the end of the dark period, and these seedlings became more resistant to chilling injury on exposure to the light. The development of chilling tolerance in tomato seedlings was a response to light and not under the control of a circadian rhythm. The recovery of leaf gas exchange following chilling was faster in seedlings chilled at the end of the light period. Diurnal variation in chilling sensitivity was associated with changes in catalase and superoxide dismutase activities. An increase in catalase and superoxide dismutase activities was observed at the end of the light period. Catalase activity was significantly higher in all stages of chilling following the light period compared to those chilled after the end of the dark period. Forty-eight hours of 14 °C acclimation or pretreatment with hydrogen peroxide conferred increased chilling tolerance to tomato seedlings. Hydrogen peroxide-treated seedlings showed little evidence of a diurnal variation in chilling sensitivity. These results support a role for light and oxidative stress in conferring increased chilling tolerance to tomato seedlings.

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Robert Brown, Laurence Sistrunk, William Aldred, and J. Benton Storey

`Stuart' pecans were harvested as soon as shucks would split in the fall of 1989 and 45 kg inshell samples were placed in 30 × 30 × 105 cm drying bins. The nuts were dried at air volumes of either 0, 1.27, 1.56, 1.84, or 2.12 m3/min down to 4% moisture. Air temperature in the drying bins was maintained at uniform 35°C with the exception of the 0 air volume treatment which was allowed to dry at room temperature. Four random samples of each treatment were held in frozen storage awaiting fatty acid analysis. Palmitic, stearic, oleic, linoleic, and linolinic fatty acids were separated in a 183 cm × 3 mm packed column using a 10% Silar 10C phase on a Gas Chrom QII, 100/120. The samples dried with a air volume of 1.27 m3/min retained a significantly higher oleic acid content than the 0 and 2.12 m3/min drying volumes. The 1.27 m3/min volume retained 64.55 % oleic acid compared with 61.37'% for the 0 velocity sample and 59.61% for 2.12 m3/min treatment. The more desirable oleic/linoleic ratio of 2.24 was found in the 1.27 m3/min sample compared to a 1.78 ratio in the 2.12 m3/min sample. Increased volume of air in the drying bins was thus deleterious to these samples because of the loss of monounsaturated fatty acid.

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Kanogwan Kerdnaimongkol, Anju Bhatia, Robert J. Joly, and William R. Woodson

Diurnal variation in the chilling sensitivity of tomato seedlings was examined. Sensitivity to chilling in tomato seedlings is a response to light and not under the control of a circadian rhythm. Chilling sensitivity is highest in seedlings chilled at the end of the dark period, and these seedlings become more resistant to chilling injury upon exposure to the light. Diurnal variation in chilling sensitivity was associated with changes in catalase and superoxide dismutase activities. The results show an increase in catalase and superoxide dismutase activities at the end of the light period. The recovery of the net photosynthesis rate following chilling was faster in seedlings chilled at the end of the light period. It is suggested that an increase in catalase and superoxide dismutase activities at the end of light period before the chilling plays a role in the resistance to chilling stress in tomato seedlings. Forty-eight hours of 14°C acclimation or hydrogen peroxide pretreatment conferred chilling tolerance to tomato seedlings and were correlated with elevated catalase activity. Acclimated seedlings still exhibited diurnal variation in chilling sensitivity while hydrogen peroxide treated seedlings showed little evidence of a diurnal variation in chilling sensitivity. Transgenic tomato plants expressing an antisense catalase gene were generated. A several-fold decrease in total catalase has been detected in the leaf extracts of transformants. Preliminary analysis of these plants indicated that modification of reactive oxygen species scavenging in plant system can lead to change in oxidative stress tolerance.

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Sami Bahri, William Aldred, Robert Brown, Laurence Sistrunk, J. Benton Storey, and Tommy Thompson

Previous work in this lab has shown that drying temperatures above 35°C will cause excessive loss of the kernel's natural light color and less oleic (18:1) oxidation to linoleic (18:2) fatty acid. The former is undesirable because of poor consumer appeal and the latter is desirable because of superiority of oleic acid in reducing low density lipoprotein in the blood plasma of consumers and a longer shelf life. The drying temperature of 35°C and an air volume of 45 CFM was superior in 1989 to 75 CFM at the same temperature and an air dried control. Lower air volumes in 1990 proved to be no better than 45 CFM at 35°C The best compromise drying regime was determined to be 45 CFM at 35°C.

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Robert A. Saftner, J. George Buta, William S. Conway, and Carl E. Sams

The effects of organosilicone and more conventional hydrocarbon surfactants on postharvest radiolabeled calcium (Ca) and on Ca solution infiltration into `Golden Delicious' apples were examined to provide a direct and more efficient pressure infiltration technique to increase fruit Ca concentration. Both radiolabeled Ca infiltration and the proportional increase in fruit Ca estimated by fruit weight gain from Ca solutions of known concentration were significantly enhanced by a range of surfactants having differing chemical structures. Two organosilicone surfactants, Silwet L-77 and Silwet L-7604, known for their greater capacity to lower the surface tension of solutions than conventional hydrocarbon surfactants, were the best among the surfactants tested at augmenting Ca infiltration. Applications of surfactants to fruit were as effective or more effective when used as a pretreatment rather than by mixing with Ca solutions. The applied atmospheric pressure necessary to infiltrate Ca to levels considered sufficient to maintain fruit firmness and resist decay during storage could be lowered in fruit treated with organosilicone surfactants. Postharvest surfactant and Ca treatments may offer a practical means of increasing the Ca concentration of apple fruit.

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Robert J. Porting, Carl E. Sams, William S. Conway, Jimmie L. Collins, and Marjorie P. Penfield

`Golden Delicious' and `Red Rome' apples were pressure infiltrated (69 kPa for 2 or 4 min) at harvest with 0, 1, 2, 3 or 4%, and 0, 2, 4, 6 or 8% CaCl2 solutions (w/v), respectively, and placed in 0°C storage. Juice was extracted from the apples after 0, 2, 4 or 6 months in storage. Sensory evaluation of the juice was conducted to determine if CaCl2 concentration affected color, off-flavors, suspended particles or overall acceptability of the juice. Juice color was judged lighter with increased CaCl2 in both cultivars. Detection of off-flavors decreased as CaCl2 was increased in juice from `Red Rome'; whereas, off-flavors increased as CaCl2 was increased in `Golden Delicious' juice. CaCl2 treatments decreased suspended particles in both cultivars. As CaCl2 was increased overall acceptability of juice from `Red Rome' increased, while acceptability of juice from `Golden Delicious' decreased.

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Robert J. Porting, Carl E. Sams, William S. Conway, Jimmie L. Collins, and Marjorie P. Penfield

`Golden Delicious' and `Red Rome' apples were pressure infiltrated (69 kPa for 2 or 4 min) at harvest with 0, 1, 2, 3 or 4%, and 0, 2, 4, 6 or 8% CaCl2 solutions (w/v), respectively, and placed in 0°C storage. Juice was extracted from the apples after 0, 2, 4 or 6 months in storage. Sensory evaluation of the juice was conducted to determine if CaCl2 concentration affected color, off-flavors, suspended particles or overall acceptability of the juice. Juice color was judged lighter with increased CaCl2 in both cultivars. Detection of off-flavors decreased as CaCl2 was increased in juice from `Red Rome'; whereas, off-flavors increased as CaCl2 was increased in `Golden Delicious' juice. CaCl2 treatments decreased suspended particles in both cultivars. As CaCl2 was increased overall acceptability of juice from `Red Rome' increased, while acceptability of juice from `Golden Delicious' decreased.

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Steven J. Guldan, Charles A. Martin, William C. Lindemann, Jose Cueto-Wong, and Robert L. Steiner

Hairy vetch (Vicia villosa Roth.), barrel medic (Medicago truncatula Gaerth.), and black lentil (Lens culinaris Medik.) were interseeded into `New Mexico 6-4' chile pepper (Capsicum annuum L.) when plants were 8 to 12 inches tall or 12 to 16 inches tall in 1993 and 1994. Hairy vetch overwintered well both years, whereas barrel medic and black lentil did not. Spring aboveground dry mass yields of hairy vetch averaged 2.11 and 2.57 tons per acre in 1994 and 1995, respectively, while N accumulation averaged 138 and 145 pounds per acre in 1994 and 1995, respectively. Forage sorghum [Sorghum bicolor (L.) Moench] dry mass yield and N accumulation were significantly higher following hairy vetch than following the other legumes or no-legume control. There was no significant difference between forage sorghum yields following barrel medic, black lentil, or the no-legume control. Fertilizer replacement values (FRV) for the legumes were calculated from regression equations for forage sorghum dry mass yield as a function of N fertilizer rate. FRV for hairy vetch were at least 7-times higher than for either barrel medic or black lentil. Hairy vetch interseeded into chile pepper and managed as a winter annual can significantly increase the yield of a following crop compared to a nonfertilized control.