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Mary W. George and Robert R. Tripepi

Plant Preservative Mixture™ (PPM), a relatively new, broad-spectrum preservative and biocide for use in plant tissue culture, was evaluated as an alternative to the use of conventional antibiotics and fungicides in plant tissue culture. Concentrations of 0.5 to 4.0 mL·L-1 were tested with leaf explants of chrysanthemum (Dendranthem×grandiflora Kitam), European birch (Betula pendula Roth), and rhododendron (Rhododendron catawbiense Michx.). PPM had little effect on the percentage of explants forming shoots and the number of shoots formed per explant in birch and rhododendron, but dramatically reduced both responses in chrysanthemum. Therefore, the effects of PPM must be evaluated for each species of interest prior to use.

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Randall P. Niedz

Controlling bacterial and fungal contamination in plant tissue cultures is a serious problem. Antibiotics are currently used but are not always effective, can alter plant growth, and are costly, and resistant strains can result with extensive use. Plant preservative mixture (PPM) contains a mixture of two isothiazolones—methylchloroisothiazolinone and methylisothiazolinone, which are a class of broad-spectrum, widely used industrial biocides. The isothiazolones used in PPM are reported by the manufacturer to be nonphytotoxic at concentrations suitable for the prophylactic control of microbial contaminants in plant tissue cultures. Our results indicate that PPM can be routinely added to tissue culture medium to control air- and waterborne bacterial and fungal contaminants effectively.

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Philip A. Stack and Francis A. Drummond

Orius is an effective predatory bug of western flower thrips on chrysanthemum. However, long days are required to prevent reproductive diapause in Orius, which is counter to the short-day flowering response in Dendranthema. Two cut flower cultivars (`Manatee Iceberg' and `Naples') and a pot cultivar (`Boaldi') were given short days, long days with broad spectrum light, and long days with supplemental blue light (430–480 nm) at critical threshold levels. Blue light at intensities of 2 to 5 μmol·m–2·s–1 had no effect on flower induction, size, or dry weight or leaf dry weight compared to the short-day control. Increasing intensity and blue light exposure reduced flowering in the cut mum cultivars. At 25C, 77% of Orius females were reproductive in blue light compared to 75% in broad spectrum and 46% in short days. Spectral quality had no effect on fecundity, survival, or insect development rate. At least 90% of Orius reproduced with blue light at 19, 22, 25, and 28C. These results indicate possibilities for providing favorable conditions for biocontrol of arthropod pests on short-day crops.

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A. Hagiladi and M. Raviv

Tissue culture plantlets of Saintpaulia ionantha and Peperomia grisco-argenta were grown for 120 days in growth boxes placed in a greenhouse. The filtercovered tops of the boxes were sloped facing south, the direction of the sun, while the walls were constructed of white styrofoam board Four types of light filters covered the frames. Two blue celluloid sheets were used to alter the sunlight spectrum: one filtered out the red (B + FR), and the other removed most of the red and far-red, FR (B - FR). Two polyethylene films were formulated as light filters and diffusers: one scattered all the transmitted light and decreased the R: FR ratio (W), while the other was neutral in respect to the sunlight spectrum and did not cause light scattering (A). Vegetative growth of Saintpaulia plants was enhanced under the light-diffusing filters, resulting in higher fresh weight and larger leaves. Saintpaulia plants flowered first under the W filter, then the A filter, and last under the B + FR filter; no flowering occurred in the absence of FR light (B - RR). There was no significant difference in the development of Peperomia plants grown under the different filters. The results are discussed in relation to plant adaptation to various environments.

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Hyeon-Hye Kim, Gregory D. Goins, Raymond M. Wheeler, and John C. Sager

Plants will be an important component of future long-term space missions. Lighting systems for growing plants will need to be lightweight, reliable, and durable, and light-emitting diodes (LEDs) have these characteristics. Previous studies demonstrated that the combination of red and blue light was an effective light source for several crops. Yet the appearance of plants under red and blue lighting is purplish gray making visual assessment of any problems difficult. The addition of green light would make the plant leave appear green and normal similar to a natural setting under white light and may also offer a psychological benefit to the crew. Green supplemental lighting could also offer benefits, since green light can better penetrate the plant canopy and potentially increase plant growth by increasing photosynthesis from the leaves in the lower canopy. In this study, four light sources were tested: 1) red and blue LEDs (RB), 2) red and blue LEDs with green fluorescent lamps (RGB), 3) green fluorescent lamps (GF), and 4) cool-white fluorescent lamps (CWF), that provided 0%, 24%, 86%, and 51% of the total PPF in the green region of the spectrum, respectively. The addition of 24% green light (500 to 600 nm) to red and blue LEDs (RGB treatment) enhanced plant growth. The RGB treatment plants produced more biomass than the plants grown under the cool-white fluorescent lamps (CWF treatment), a commonly tested light source used as a broad-spectrum control.

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Andrea B. da Rocha and Ray Hammerschmidt

A major challenge facing horticultural crop production is the need to provide field and postharvest disease control measures that help maintain high quality plant products. Producers and consumers also expect high quality produce with minimal or no pesticide residues and competitive prices. The chemical management of disease is further complicated by the development of fungicide resistance in many important pathogens. Because of these concerns, an alternative or complementary approach is the use of disease resistance inducers that activate the natural defenses of the plant. Induced disease resistance in plants has been studied in many different pathosystems for nearly a century. Resistance to plant disease can be induced systemically by prior infection with pathogens, by certain non-pathogenic microbes that colonize the surface of roots and leaves, or by chemicals. The application of resistance inducers should protect plants through the induction of defenses that are effective against a broad spectrum of pathogens. Over the last few years, a number of materials that could potentially be used as inducers of resistance in horticultural crops have been identified. Some of these materials are already commercially available. Although induced resistance is known to provide a broad spectrum of disease suppression, it may not be a complete solution because variation in the efficacy of disease resistance induction has been observed. The variation in the response may be dependent on the plant species and even cultivars, as well as variability in the spectrum of pathogens that resistance can be induced against. Induction of resistance depends on the activation of biochemical processes that are triggered in the plant, and therefore a lag time between treatment and expression of resistance occurs. This lag effect may limit the practical application of disease resistance inducers. Since the efficacy of the inducers also depends on the part of the plant that was treated, the product delivery (i.e., how the inducers would be applied in order to optimize their action) is another factor to be considered. Some studies have shown that there may be side effects on growth or yield characteristics when certain inducers are used. Understanding the biochemical interactions occurring between plants, pathogens and the inducers will provide information that may be useful for the optimization of this new approach on disease control. Approaches to integrate induced resistance with other management practices need to be investigated as a means to aid the development of sustainable disease management programs that are effective as well as economically and environmentally sound.

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Jodie Benson and John Kelly

Tomato and pepper transplants were grown in an environment with a high red to far-red light ratio, to determine if this was an effective method for controlling plant height. This light environment was provided by placing plants under copper sulfate filters, which absorb most of the light in the far-red region of the spectrum. Copper sulfate solutions were 4%, 8%, and 16% w/v. Tomato transplants grown under the filters were approximately 40% shorter than control plants, had less dry weight and leaf area, and increased leaf chlorophyll. Leaf number data was less clearly affected. Differences were not observed among the three different CuSO4 concentrations. Similar results were observed for peppers. Field trials on tomatoes indicated that total yield, earliness of fruiting, and fruit quality were not affected by growing transplants under the CUSO4 filters.

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Margaret J McMahon and John W. Kelly

The growth of Rosa × hybrida and Exacum affine under different spectral filters was evaluated. Three filters that altered light quality were developed. One, a red textile dye, filtered out much of the blue/green portion of the light spectrum but did not change far-red to red (FR/R) light ratio. Another, a blue textile dye, raised FR/R by filtering out a portion of red light. The third, a salt (copper sulfate) lowered FR/R by filtering out a greater portion of far-red than red light. Two controls were used that did not alter light quality. The filters were installed in specally built growth chambers. Photosynthetic Photon Flux Density (PPFD) was adjusted to equal values in each chamber.

Plants of both species were significantly shorter and had higher leaf chlorophyll, when grown under the low FR/R filter.

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N.G. Creamer, M.A. Bennett, J. Cardina, and E.E. Regnier

Little research has been conducted to quantify allelopathic suppression of weeds in the field. The objectives of this study were to develop an adequate control for separating physical from allelochemical effects, use the control to quantify allelochemical suppression in the field, and determine whether a mixture of cover crops would provide a broader spectrum of weed control than single species. Hairy vetch, rye, crimson clover, and barley were cut into 5-cm pieces, shaken in distilled water (pH 6) to leach allelochemicals, and redried. A seed germination bioassay confirmed that leached cover crops were nontoxic to germinating seeds. Physical suppression of Eastern black nightshade by the four cover crop species occurred in the field study, as did allelochemical suppression by crimson clover. Only rye physically suppressed yellow foxtail, and none of the cover crops suppressed yellow foxtail allelochemically.

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H.S. Costa, K.L. Robb, and C.A. Wilen

A field study was conducted to assess the effect of various commercially available polyethylene plastic greenhouse coverings on the persistence of viable spores of the microbial insecticide Beauveria bassiana. Selected coverings blocked the transmission of UV light with wavelengths of 360 nm and below or 380 nm and below. Two coverings also contained an infrared blocking component. A commercial formulation of B. bassiana was applied for 3 consecutive weeks to plants growing in the plastic covered hoop houses. The percentage of viable spores was calculated up to 13 days after the final application. The persistence of viable B. bassiana spores was significantly longer under the plastic that blocked a greater portion of the UV spectrum (<380 nm) than the plastics that only blocked UV wavelengths below 360 nm. One week after application, percentage of spore germination was at least twice as high under the <380 nm blocking plastic compared to <360 nm blocking plastics.