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K. Tano, L.Z. Lee, F. Castaigne, and J. Arul

Use of modified atmosphere (MA) as an adjunct to low temperature can be effective method for prolonging the shelflife of fresh fruits and vegetables. However, if storage temperature fluctuates, anoxic conditions can result and, consequently, the fresh produce quality can deteriorate rapidly. The objective of this investigation was to evaluate the effects of temperature fluctuation on the atmosphere inside the package and on the quality of packaged produce. Mushrooms (A. bisporus, U3 Sylvan 381) were packaged in rigid containers (4 liters) fitted with diffusion windows to obtain an atmosphere of 5% O2 and 10% CO2 at 4C. Temperature fluctuation had a major impact to the atmosphere inside package. During the first fluctuation sequence, O2 level depleted to 1.5% and CO2 increased to 18%. When the temperature returned to 4C during the next sequence, CO2 level fell back to 10%, but O2 level remained at 1.5%. The quality of mushrooms stored under temperature-fluctuating conditions was severely affected, as indicted by the extent of browning, loss of texture, and level of ethanol in the tissue compared to mushrooms stored at constant temperature. It was clear from this experiment that under temperature fluctuation, even it occurs once, can seriously compromise the benefits of MA packaging and safety of the packaged product. It is thus necessary that MA packaging compensate for the additional permeability required that is caused by storage temperature fluctuations.

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Mark H. Brand

Although it is commonly recommended that shoot tip cultures be initiated from actively growing shoots, it has been demonstrated that shoot tips collected during the period of rapid shoot extension fail to produce shoot proliferating cultures. Shoot tips of Halesia Carolina and Malus `Golden Delicious' were collected at 2 week intervals from budbreak to summer dormancy and placed on medium containing 0, 4.5, 11.0, 22.5 and 44.5 uM benzyladenine (BA) to determine if elevated BA concentrations could overcome seasonal patterns of shoot proliferation potential (SPP). Both species reached maximum SPP 4 weeks post-budbreak (PBB), and exhibited a second window of high SPP during weeks 10 and 12. Elevated BA concentrations failed to overcome poor SPP exhibited by shoot tips harvested 6 to 8 weeks PBB. Shoot tips collected at 10 to 12 weeks PBB responded more favorably to higher exogenous BA concentrations than shoot tips collected at 2, 4, 6, or 8 weeks PBB. It appears as though seasonal fluctuations in SPP involve other endogenous factors in addition to cytokinins.

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Christopher Lindsey, Gate Kline, and Mark Zampardo

An interactive computer-based system was designed to improve student plant identification skills and knowledge of ornamental, cultural, and usage information in a woody landscape plant materials course. The program is written for use under ToolBook, a Microsoft Windows based program, and incorporates 256-color high-resolution images and text into a single interactive computer program. Features include: a slideshow that allows students to select which genera and plant characteristics are to be viewed and in what order with the option of an interactive quiz, seeing the names immediately, or after a delay; side by side comparison of any image or text selection; and encyclopedic entries, all with a user-defined path and pace of study.

The system is being used to study how students learn the information presented to them via computer technology and which program features are most useful for improving identification skills and knowledge of other plant features. The computer tracks and logs all activity by students on the system for analysis.

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Kitren G. Weis, Stephen M. Southwick, and George C. Martin

Gibberellic acid reduces return bloom in many fruit tree species. Reducing bloom may cut costs of hand thinning apricot, peach and plum fruit. Sprays of 250 ppm GA, during floral bud evocation (June 1993) resulted in bud death and abscission as determined by light microscopy sections in `Patterson' apricot (Prunus armeniaca L). GA treatment in May did not cause observable effects. August treatments, immediately prior to floral initiation, did not impede differentiation. Treatment of `Elegant Lady' peach (Prunus persica [L.] Batsch.) buds with 75-250 ppm GA, in late June, 1993 (evocation phase) did not have any discernable effects in that season with respect to abscission or differentiation. Treated peach buds differentiated simultaneously with untreated buds in early August. The patterns of response to GA treatment imply `windows of opportunity' with respect to effectiveness of GA treatments. The specific response suggests that apricot buds possess differing levels of sensitivity to GA treatment and probably reflect distinct phases in transition to flowering. In August buds were already `determined' and were in a potentially floral state that was irreversible.

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Donald T. Krizek, Steven J. Britz, and Roman M. Mirecki

The influence of ambient UV radiation on growth and flavonoid concentration of Lactuca sativa L. (`New Red Fire' lettuce) was examined. Plants were grown outdoors for 31 days from seed in window boxes covered with one of three different UV filters—UV transparent tefzel (10%T, 245 nm), UV-B-absorbing polyester (10%T, 319 nm), or UV-Aand UV-B-absorbing Llumar (10%T, 399 nm). Plants were grown in plastic pots filled with vermiculite and subirrigated with nutrient solution. Lettuce plants grown in the absence of solar UV-A and UV-B radiation showed a significant increase in leaf number and biomass of tops and roots as compared to those grown under ambient UV-A and UV-B. They also had a lower concentration of flavonoids and other UV-absorbing substances at 270, 300, and 330 nm (on both an area and on a dry-weight basis). These findings should be of interest to researchers involved in protected cultivation because the transmission of UV-B radiation is greatly attenuated by standard greenhouse glass. Our results also have implications for human nutrition, since bioflavonoids are important as antioxidants.

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Prem L. Bhalla and Katherine Tozer

Plants of genus Scaevola (family, Goodeniaceae), commonly known as “fan flowers,” are mostly endemic to Australia. Commercially popular species are Scaevola aemula, S. albida, S. striata, and S. phlebopetala. These plants are used as ground covers in Australia and as hanging baskets, window boxes, and garden bed plants in Europe and America. Two aspects of in vitro culture of Scaevola are reported here; micropropagation and direct shoot regeneration. A number of commercially available cultivars of S. aemula, S. phlebopetala, S. striata and wild-collected S. phlebopetala, S. glandulifera, S. hookeri, and S. ramonissima were used for micropropagation experiments. Micropropagation medium contained salts, vitamins, L-cysteine, sucrose, and agar. Tissue-cultured shoots were rooted in hormone-free medium. A high survival percentage (>95%) was obtained when plants were transferred to soil under glasshouse conditions. Results on in vitro shoot induction and regeneration response of leaf, stem, root, node, and flower explants of two horticulturally important species of the Australian fan flower, Scaevola aemula and Scaevola striata arealso presented. Of all the explants tested, node explants of these species were the first to respond in tissue culture. Maximum number of shoot induction and regeneration was achieved from node explants of Scaevola aemula and node and stem explants of Scaevola striata. More than 95% of the regenerated shoots were rooted on the medium supplemented with 4 mg/L of IBA. The significance of above findings in assisting breeding program for new horticultural desirable cultivars of Australian fan flowers will be discussed.

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D.M. Glenn, D.L. Peterson, and S.S. Miller

This study evaluated the total and marketable yield of three peach cultivars [Prunus persica (L.) Batsch. `Autumnglo', `Harvester', and `Redhaven'] when mechanical pruning and harvesting systems were used and trees were grown under three irrigation regimes. All cultivars were trunk-shaken using an experimental inertial shaker on an over-the-row (OTR) shake–catch harvester. `Autumnglo' also was hand-harvested at all irrigation regimes. Fruit damage was not significantly affected by irrigation. A significant source of fruit damage was pruning debris that remained in the canopy after hedging and became lodged in the fruit-conveying system, resulting in cultivar effects on fruit damage. Total yield of firm-ripe fruit was similar among cultivars in 1987 and 1988. However, `Autumnglo' trees had a higher percentage of marketable fruit than `Redhaven' or `Harvester' in 1987 and 1991. Mechanical harvesting appeared to accelerate the decline of `Autumnglo' as shown by tree deaths and greater symptom expression of Prunus necrotic ringspot virus. The potential for a single mechanical harvest of peaches is limited because of the difficulty in managing the ripening window, the high potential for fruit damage, and the possibility of accelerated tree decline for disease-susceptible cultivars.

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Mark Zampardo, Gary Kling, and Christopher Lindsey

An integrated teaching system was developed and tested on students enrolled in a woody landscape plants identification course. A Microsoft Windows-based system incorporates high-quality digital images and text in an interactive computer environment. The goal of the software program was to enhance retention of course material through the use of many images along with accompanying text and a variety of special features. In alternating 4-week periods, one-half of the students in class were randomly selected and given password access to the software. The other half served as a control group. All students continued to receive traditional lecture and laboratory presentations of the material, including weekly slide coverage of each plant. The exams incorporated material from lectures and labs and included slide images from which students were to identify the plant taxa. The study took into account time on the computer and test scores. Results showed that increased time on the computer was positively correlated with increased test scores. Student performance on the slide portions of the exams were consistently higher for computer users than control groups.

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Christopher Lindsey, Gary Kling, and Mark Zampardo

UIPLANTS is a program developed under Microsoft Windows to help students in woody plant materials courses. Its many options include an encyclopedic format that displays 256-color high-resolution images of plant identification characteristics and ornamental features coupled with text, side by side image comparisons, “book markers” to return to selected screens, and a slide show that runs a display of images in a user-defined format. The system is being used to study how students learn information presented to them through computers and which program features are most effective in improving plant knowledge. Through computer logging of all student activity within the program and surveys given to the test groups, some basic usage patterns were derived. Students using the program with no incentive tended to use the program in a more comprehensive manner, switching back and forth between the slide show and encyclopedic entries with equal time spent in each. The comparison and “bookmark” features were used but less frequently. Half of the students, given an extra credit incentive based on time, followed this same usage pattern, but the other half simply used the slide show with minimal student–computer interaction.

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J.-L. Arsenault, S. Poulcur, C. Messier, and R. Guay

WinRHlZO™ is a new root measuring system (1993) based on an optical scanner instead of a video camera. Scanners produce high-quality images, free of illumination problems, over large areas (typically 11 × 17 inches). They are also extremely easy to use, and do not need to be recalibrated each time the optical set up or the resolution is changed. Different lighting systems are also available. WinRHlZO™ is an interactive system; the user can see on screen with color codes what the system is measuring and can make corrections if needed. WinRHlZO™ has the capacity to detect overlapping root parts and to compensate for them in the final results. It measures total length, projected area, surface area, and root length for different width intervals chosen by the user. The results are shown in a printable histogram placed above the image. The system also counts root tips and branching points. It is possible to verify the width at different points along the root by clicking them in the image. WinRHlZO™ can analyze whole images or different parts of them. It runs on IBM-compatible software under Microsoft Windows 3.1 or NT, and on Macintosh computers.