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P. Perkins-Veazie and J.K. Collins

Application of modified-atmosphere storage (MA) (high carbon dioxide and/or low oxygen) extends the shelf life of several fruits. This study was done to determine the effects of MA on quality and flavor of blackberries. `Navaho' and `Arapaho' blackberries were harvested in 1998 and 1999, precooled overnight at 2 °C, and placed in 0.5-L treatment jars. Treatments of 15% CO2/10% O2 or of air (0.03% CO2/21% O2) were applied at 2 °C for 3, 7, or 14 days. After treatment application, jars were held at 2 °C for an additional 11, 7, or 0 days, respectively. Seven and 14 days of application of CO2 reduced the incidence of decayed and leaky berries by 10% to 20% for both `Arapaho' and `Navaho', but firm berries decreased 10% after 14 days of treatment. Titratable acidity was slightly lower, and pH higher, in control fruit but soluble solids content was not affected by treatment. Anthocyanin content was not affected by treatment in `Arapaho' berries but was lower in `Navaho' berries after 7 and 14 days of treatment. Samples taken for taste tests after 3 and 7 days of treatment had no off-odors or off-flavors. `Arapaho' and `Navaho' blackberries benefitted from high CO2 storage, with a minimum of 7 days of treatment application needed to increase marketable berries by 10%.

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H. John Elgar, Douglas M. Burmeister, and Christopher B. Watkins

`Braeburn' apple (Malus ×domestica Borkh.) fruit can be susceptible to the development of an internal disorder called “`Braeburn' browning disorder” (BBD). Factors associated with development of this disorder were investigated. Susceptibility to injury was greater in fruit exposed to 2 or 5 kPa CO2 than to 0 kPa CO2 during storage. Susceptibility also increased with decreasing O2 partial pressure in the range of 5 to 1 kPa in the storage atmosphere. However, fruit stored in 1 kPa O2 remained firmer than those stored at higher partial pressures, regardless of CO2 level. BBD appeared to develop during the first 2 weeks of storage, and delays in air at 0 °C prior to controlled-atmosphere (CA) storage decreased incidence and severity of the disorder. The incidence of BBD was also reduced when the time to establish CA conditions was prolonged. We recommend that `Braeburn' apples be stored under CA conditions of ≤1.0 kPa CO2 and 3.0 kPa O2. Delayed application of CA for 2 weeks after fruit enter the coldstorage may also reduce development of BBD.

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R.M. Wheeler, C.L. Mackowiak, N.C. Yorio, L.M. Ruffe, and G.W. Stutte

Radish (Raphanus sativus cv. Giant White Globe) and lettuce (Lactuca sativa cv. Waldmann's Green) plants were grown for 25 days in growth chambers at 23 °C, ≈300 μmol·m-2·s-1 PPF, and 18/6 photoperiod, and four CO2 concentrations: 400, 1000, 5000, and 10,000 μmol·mol-1. Average total dry mass (g/plant) at the 400, 1000, 5000 and 10,000 μmol·mol-1 treatments were 6.4, 7.2, 5.9, and 5.0 for radish and 4.2, 6.2, 6.6, and 4.0 for lettuce. Each species showed an expected increase in yield as CO2 was elevated from 400 to 1000 μmol·mol-1, but super-elevating the CO2 to 10,000 μmol·mol-1 resulted in suboptimal growth. In addition, many radish leaves showed necrotic lesions at 10,000 μmol·mol-1 by 17 days and at 5000 μmol·mol-1 by 20 days. These results are consistent with preliminary tests in which radish cvs. Cherry Belle, Giant White Globe, and Early Scarlet Globe were grown for 16 days at 400, 1000, 5000, and 10,000 μmol·mol-1. In that study, `Giant White Globe' produced the greatest total dry mass at 1000 (3.0 g/plant) and 5000 μmol·mol-1 (3.0 g/plant), and the least at 10,000 μmol·mol-1 (2.2 g/plant). `Early Scarlet Globe' followed a similar trend, but `Cherry Belle' showed little difference among CO2 treatments. Results suggest that super-elevated CO2 can depress growth of some species, and that sensitivities can vary among genotypes.

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Barbara L. Goulart, Philip E. Hammer, Kathleen B. Evensen, Wojciech Janisiewicz, and Fumiomi Takeda

The effects of preharvest applications of pyrrolnitrin (a biologically derived fungicide) on postharvest longevity of `Bristol' black raspberry (Rubus occidentals L.) and `Heritage' red raspberry [R. idaeus L. var. strigosus (Michx.) Maxim] were evaluated at two storage temperatures. Preharvest fungicide treatments were 200 mg pyrrolnitrin/liter, a standard fungicide treatment (captan + benomyl or iprodione) or a distilled water control applied 1 day before first harvest. Black raspberries were stored at 18 or 0 ± lC in air or 20% CO2. Red raspberries were stored at the same temperatures in air only. Pyrrolnitrin-treated berries often had less gray mold (Botrytis cinerea Pers. ex Fr.) in storage than the control but more than berries treated with the standard fungicides. Storage in a modified atmosphere of 20% CO2 greatly improved postharvest quality of black raspberries at both storage temperatures by reducing gray mold development. The combination of standard fungicide or pyrrolnitrin, high CO2, and low temperature resulted in more than 2 weeks of storage with less than 5% disease on black raspberries; however, discoloration limited marketability after≈ 8 days under these conditions. Chemical names used: 3-chloro-4-(2'-nitro-3'-chlorophenyl) -pyrrole (pyrrolnitrin); N-trichloromethylthio-4-cyclohexene-l12-dicarboximide (captan); methyl 1-(butylcarbamoyl) -2-benzimidazolecarbamate) (benomyl); 3-(3,5 -dichlorophenyl) -N-(l-methylethyl -2,4-dioxo-l-imi-dazolidinecarboxamide (Rovral, iprodione).

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Amanda L. Broome and Ellen B. Peffley

This research evaluated, for the NASA ALS program, the effect of spacing and harvest intervals on edible biomass of green salad onions grown at two CO2 levels. Shoot biomass of Japanese bunching onion (Allium fistulosum), bulbing onion (A. cepa), and chives (A. schoenoprasum) grown at 10-, 15-, and 20-mm spacings harvested at 7- and 14-day intervals, seven and four harvests, respectively, over 70 days were compared. Onions were grown hydroponically in growth chambers, 16-hour light/8-hour dark, 24/20 °C, 75/99% at ∼450 and 1200 ppm CO2. The design was a completely randomized block with repeated measures; subsamples were plants completely surrounded by neighboring plants. Weekly shoot removal began 28 days after planting (dap); destructive harvest was 70 dap. Length and diameter of longest leaf, weight, and number of leaves/tillers were taken at each harvest; bulb caliper and weight were taken 70 dap. Bunching and bulbing onion leaves were longest at 28 dap and decreased over time; chives were slow to establish but 70 dap had longest leaves. Leaf diameter of all species increased as spacing increased. At 56 through 70 dap chives at all three spacings produced more leaves. Mean weight of shoots differed significantly at 20-mm spacing: chives the least, bulbing onion the most. Bulb weight for bulbing onion and chives increased with increased spacing; bulbing onion weighed significantly more at 15- and 20-mm spacings compared to the other species and spacings. Chives grown at 20-mm spacing had tillering clumps of rhizomes. Total edible biomass weight (bulb, pseudostem, and shoots) of bulbing onion grown at 10-mm spacing exhibited similar ontogeny to chives grown at 10- and 15-mm spacings; bulbing onion grown at 20-mm spacing had the most edible biomass. On average, biomass was greatest in plants grown at 1200 ppm CO2.

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Wenwei Jia, L.A. Weston, and J. Buxton

Tomato and pepper seedlings were grown in six controlled environmental chambers with three different temperature levels (high:24/16°C, medium:20/12°C, and low:16/8°C) and two CO2 levels (1500 ppm and ambient) after cotyledons had unfolded. After 4 weeks, seedlings were planted into 15 cm pots. After 4 weeks, another set were transplanted to the field on 5/13 and arranged with 4 replications in a randomized complete block design. Only temperature treatment had a significant influence on the number of flowers developed in greenhouse experiments. However, for field transplanted seedlings, CO2 enrichment had a significant effect on flower formation and increased total flower numbers and fruit numbers in the early growth stages in field. Temperature also influenced seedling height. In other experiments, cold treatments were given to tomato and pepper seedlings. Seedlings were treated with 13°C temperatures for 0, 1 or 2 weeks after cotyledons unfolded. Results indicate that tomato seedlings with either 1 or 2 weeks of cold treatment had greater dry weight and leaf numbers and larger and more mature flower buds than those given no cold treatment. Pepper seedlings receiving 2 weeks of cold treatment showed similar increases compared to those receiving 0 or 1 weeks of cold treatment. The earliest flower initials were observed microscopically when tomato had only one visible leaf and pepper had 8 or 9 visible leaves. These results indicate that cold treatments should be started as soon as the cotyledons have unfolded to hasten flower formation.

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Antonio Figueira, Anna Whipkey, and Jules Janick

Cacao (Theobroma cacao) has long been considered a recalcitrant species in regard to microproagation. Although axillary shoots from cotyledonary nodes will proliferate and grow in vitro provided either cotyledons or roots are attached, excised shoots fail to grow in spite of conventional medium and hormonal modifications. Charcoal supplemented medium and rapid medium change are only marginally effective in inducing shoot elongation. The recalcitrance of cacao appear to be due to the presence of gums which are produced from stem tissues in response to wounding. However, growth of axillary cotyledonary shoots as well as mature shoots was obtained under conditions of high CO2 (20,000 ppm) and high light (quantum flux of 200 μmol m-2s-1) with or without sugar. Under these conditions leaves develop and shoots elongate which can be subdivided and subcultured. Shoots root under these conditions in vitro. We hypothesize that growth of cacao shoots in response to high CO2 is due to translocation of metabolizes from photosynthesizing leaves and stems.

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Marc van Iersel and Jong-Goo Kang

Subirrigation is an economically attractive irrigation method for producing bedding plants. Because excess fertilizer salts are not leached from the growing medium, salts can accumulate in the growing medium. Fertilizer guidelines developed for overhead irrigation may not be appropriate for subirrigation systems. Our objective was to quantify the effect of the fertilizer concentration (N at 0, 135, 285, and 440 mg·L–1) on whole-plant CO2 exchange and growth of subirrigated pansies. Whole plant CO2 exchange rate (net photosynthesis and dark respiration) was measured once every 10 min for 31 days. Whole-plant photosynthesis, dark respiration, and carbon use efficiency increased during the experiment. Fertilizer concentration started to affect the growth rate of the plants after approximately 7 days. Maximum photosynthesis and growth were achieved with N at about 280 mg·L–1 in the fertilizer solution [electrical conductivity = 2 dS·m–1]. Growth was reduced by ≈10% when the plants were fertilized with N at 135 and 440 mg·L–1 compared to 280 mg·L–1. Growth of plants watered without any fertilizer was greatly reduced, and plants showed symptoms of N and K deficiency. The size of the root system decreased and the shoot: root ratio increased with increasing fertilizer concentration, but the size of the root system was adequate in all treatments. These results indicate that subirrigated pansies can tolerate a wide range of fertilizer concentrations with relatively little effect on plant growth.

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Tracy A. Ohler and Cary A. Mitchell

The vigorous growth habit and tolerances to heat, water, and acid stresses suggest cowpea as a candidate species for Controlled Ecological Life-Support Systems (CELSS). The low fat, high protein, moderate carbohydrate content of the edible leaves and seeds complement cereal grains in the vegetarian diets planned for CELSS. Cowpea canopy densities of 3.6, 7.2, 10.7, and 14.3 plants·m-2 were grown under CO2 levels of 400 or 1200 μl·l-1. Plants were grown in a deep-batch recirculating hydroponic system. pH was maintained at 5.5 by a pH controller with an in-line electrode. The nutrient solution was replaced as needed and sampled weekly for analysis by inductively coupled plasmaatomic emission spectrometry. Fluorescent lights provided 674±147 μmol·m-2s-1 PAR for an 8-hour photoperiod. Day/night temperature was maintained at 27/25°C. CO2 draw-down within the growth chamber was measured to calculate net photosynthesis. Power consumption was metered and canopy quantum efficiency was calculated. Crop yield rate (g·m-2·d-1). harvest index (% edible biomass), and yield efficiency (edible g·m-2·d-1·(nonedible g)-1) were determined to evaluate the productivity of cowpea for a CELSS. This study was supported by NASA Grant NAGW-2329.

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Li-Song Chen, Brandon R. Smith, and Lailiang Cheng

Own-rooted 1-year-old `Concord' grapevines (Vitis labruscana Bailey) were fertigated twice weekly for 11 weeks with 1, 10, 20, 50, or 100 μm iron (Fe) from ferric ethylenediamine di (o-hydroxyphenylacetic) acid (Fe-EDDHA) in a complete nutrient solution. As Fe supply increased, leaf total Fe content did not show a significant change, whereas active Fe (extracted by 2,2′-dipyridyl) content increased curvilinearly. Chlorophyll (Chl) content increased as Fe supply increased, with a greater response at the lower Fe rates. Chl a: b ratio remained relatively constant over the range of Fe supply, except for a slight increase at the lowest Fe treatment. Both CO2 assimilation and stomatal conductance increased curvilinearly with increasing leaf active Fe, whereas intercellular CO2 concentrations decreased linearly. Activities of key enzymes in the Calvin cycle, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), NADP-glyceraldehyde-3-phosphate dehydrogenase (GAPDH), phosphoribulokinase (PRK), stromal fructose-1,6-bisphosphatase (FBPase), and a key enzyme in sucrose synthesis, cytosolic FBPase, all increased linearly with increasing leaf active Fe. No significant difference was found in the activities of ADP-glucose pyrophosphorylase (AGPase) and sucrose phosphate synthase (SPS) of leaves between the lowest and the highest Fe treatments, whereas slightly lower activities of AGPase and SPS were observed in the other three Fe treatments. Content of 3-phosphoglycerate (PGA) increased curvilinearly with increasing leaf active Fe, whereas glucose-6-phosphate (G6P), fructose-6-phosphate (F6P), and the ratio of G6P: F6P remained unchanged over the range of Fe supply. Concentrations of glucose, fructose, sucrose, starch, and total nonstructural carbohydrates (TNC) at both dusk and predawn increased with increasing leaf active Fe. Concentrations of starch and TNC at any given leaf active Fe content were higher at dusk than at predawn, but both glucose and fructose showed the opposite trend. No difference in sucrose concentration was found at dusk or predawn. The export of carbon from starch breakdown during the night, calculated as the difference between dusk and predawn measurements, increased as leaf active Fe content increased. The ratio of starch to sucrose at both dusk and predawn also increased with increasing leaf active Fe. In conclusion, Fe limitation reduces the activities of Rubisco and other photosynthetic enzymes, and hence CO2 assimilation capacity. Fe-deficient grapevines have lower concentrations of nonstructural carbohydrates in source leaves and, therefore, are source limited.