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  • Author or Editor: Christopher S. Brown x
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Plants were grown under light-emitting diode (LED) arrays with various spectra to determine the effects of light quality on the development of diseases caused by tomato mosaic virus (ToMV) on pepper (Capsicum annuum L.), powdery mildew [Sphaerotheca fuliginea (Schlectend:Fr.) Pollaci] on cucumber (Cucumis sativus L.), and bacterial wilt (Pseudomonas solanacearum Smith) on tomato (Lycopersicon esculentum Mill.). One LED (660) array supplied 99% red light at 660 nm (25 nm bandwidth at half-peak height) and 1% far-red light between 700 to 800 nm. A second LED (660/735) array supplied 83% red light at 660 nm and 17% far-red light at 735 nm (25 nm bandwidth at half-peak height). A third LED (660/BF) array supplied 98% red light at 660 nm, 1% blue light (BF) between 350 to 550 nm, and 1% far-red light between 700 to 800 nm. Control plants were grown under broad-spectrum metal halide (MH) lamps. Plants were grown at a mean photon flux (300 to 800 nm) of 330 μmol·m-2·s-1 under a 12-h day/night photoperiod. Spectral quality affected each pathosystem differently. In the ToMV/pepper pathosystem, disease symptoms developed slower and were less severe in plants grown under light sources that contained blue and UV-A wavelengths (MH and 660/BF treatments) compared to plants grown under light sources that lacked blue and UV-A wavelengths (660 and 660/735 LED arrays). In contrast, the number of colonies per leaf was highest and the mean colony diameters of S. fuliginea on cucumber plants were largest on leaves grown under the MH lamp (highest amount of blue and UV-A light) and least on leaves grown under the 660 LED array (no blue or UV-A light). The addition of far-red irradiation to the primary light source in the 660/735 LED array increased the colony counts per leaf in the S. fuliginea/ cucumber pathosystem compared to the red-only (660) LED array. In the P. solanacearum/ tomato pathosystem, disease symptoms were less severe in plants grown under the 660 LED array, but the effects of spectral quality on disease development when other wavelengths were included in the light source (MH-, 660/BF-, and 660/735-grown plants) were equivocal. These results demonstrate that spectral quality may be useful as a component of an integrated pest management program for future space-based controlled ecological life support systems.

Free access

Plant invasions pose a serious threat to biodiversity, agricultural production, and land value throughout the world. Due to Florida’s unique climate, population expansion, expansive coastline, and number of seaports, the state is especially vulnerable to non-native plant naturalization and spread. Invasive plant management programs were shown to have higher success rates with fewer resources when invasives were managed soon after non-native plants were observed. However, some newly emerging invasive plants may go undetected due to their resemblance with native species or other invasive plants. The objective of this review is to highlight a few key invasive plants in Florida that have native lookalikes. While morphological differences are discussed, the primary goal is to discuss management implications of misidentification and delayed response times, as well as the need for plant identification guides that include information on how to distinguish problematic invasive plants from similar native species.

Open Access

Light-emitting diodes (LEDs) are a potential irradiation source for intensive plant culture systems and photobiological research. They have small size, low mass, a long functional life, and narrow spectral output. In this study, we measured the growth and dry matter partitioning of `Hungarian Wax' pepper (Capsicum annum L.) plants grown under red LEDs compared with similar plants grown under red LEDs with supplemental blue or far-red radiation or under broad spectrum metal halide (MH) lamps. Additionally, we describe the thermal and spectra1 characteristics of these sources. The LEDs used in this study had a narrow bandwidth at half peak height (25 nm) and a focused maximum spectral output at 660 nm for the red and 735 nm for the far-red. Near infrared radiation (800 to 3000 nm) was below detection and thermal infrared radiation (3000 to 50,000 nm) was lower in the LEDs compared to the MH source. Although the red to far-red ratio varied considerably, the calculated phytochrome photostationary state (φ) was only slightly different between the radiation sources. Plant biomass was reduced when peppers were grown under red LEDs in the absence of blue wavelengths compared to plants grown under supplemental blue fluorescent lamps or MH lamps. The addition of far-red radiation resulted in taller plants with greater stem mass than red LEDs alone. There were fewer leaves under red or red plus far-red radiation than with lamps producing blue wavelengths. These results indicate that red LEDs may be suitable, in proper combination with other wavelengths of light, for the culture of plants in tightly controlled environments such as space-based plant culture systems.

Free access

Abstract

Carbohydrates were measured in young apple (Malus domestica Borkh.) trees throughout the period of 28 Mar. 1983 to 16 Apr. 1984. Two rootstocks, M.9 (full dwarf) and MMIII (vigorous) and 2 scion cultivars, ‘Redchief and ‘Northern Spy’ were used in the 4 possible combinations. Trees were separated into 5 classes of vegetative tissue and analyzed for starch, sorbitol, and soluble sugars. Dry weights also were measured. Trees of MMIII had a greater dry weight in the above and below ground portions than trees on M.9. Carbohydrate contents followed a similar pattern. ‘Northern Spy’ scions had greater dry weight and carbohydrate content in the above ground portion than ‘Redchief. ‘Redchief had greater dry weight and carbohydrate content in the below ground portion than ‘Northern Spy’. Above ground starch content and below ground sorbitol and soluble sugar content did not follow this pattern.

Open Access

Abstract

Leaf expansion, carbon exchange rate (CER), mass carbon transfer (MCT), and carbohydrate pools were measured in one-year-old apple trees throughout the growing season. Two rootstocks, M.9 (full dwarf) and MM111 (vigorous) and 2 scion cultivars, ‘Redchief and ‘Northern Spy’ were used in all 4 combinations to give a wide range in growth vigor. Leaves of trees on MMIII had slightly higher CER than those on M.9. MCT was higher in ‘Northern Spy’ than in ‘Redchief’. Leaves of trees on MMIII had higher daily accumulations of starch and sorbitol than those on M.9; however, when these accumulations were expressed as a percentage of CER, the differences were not significant. ‘Northern Spy’ leaves showed no net dry weight gain over 24 hr, whereas ‘Redchief leaves did. About 17% of the leaf dry weight was not accounted for by nonstructural carbohydrates or MCT in ‘Redchief’ leaves. The morning starch concentration for all the trees increased throughout the season. The specific leaf weight of ‘Redchief was higher than for ‘Northern Spy’ on all dates. Specific leaf weight also increased throughout the season. Sorbitol accumulation rate in the leaf decreased from a mid-season high, whereas sucrose accumulation rate increased from mid-season. Starch accumulation rate in the leaf also decreased from a midseason high. Accumulation rates of starch and transport carbohydrates remained parallel throughout the growing season.

Open Access

Abstract

An enzymatic assay for sorbitol in organs of apple (Malus domestica Borkh.) is described. Sorbitol concentrations in ethanolic extracts of apple leaves, stems, roots, and fruit can be measured by detecting optical density changes at 340 nm resulting from the reduction of NAD + coupled with the conversion of sorbitol to D-fructose by sorbitol dehydrogenase. The assay is unaffected by normal concentrations of fructose, glucose, or sucrose in the tissue. Sorbitol concentrations determined by the enzymatic assay were verified by HPLC analysis of the same tissue samples.

Open Access

A nutrient delivery system that may have applicability for growing plants in microgravity is described. The Vacuum-Operated Nutrient Delivery System (VONDS) draws nutrient solution across roots that are under a partial vacuum at ≈91 kPa. Bean (Phaseolus vulgaris L. cv. Blue Lake 274) plants grown on the VONDS had consistently greater leaf area and higher root, stem, leaf, and pod dry weights than plants grown under nonvacuum control conditions. This study demonstrates the potential applicability of the VONDS for growing plants in microgravity for space biology experimentation and/or crop production.

Free access

Orientation of root growth on earth and under microgravity conditions can possibly be controlled by hydrotropism-growth toward a moisture source in the absence of or reduced gravitropism. A porous-tube water delivery system being used for plant growth studies is appropriate for testing this hypothesis since roots can be grown aeroponically in this system. When the roots of the agravitropic mutant pea ageotropum (Pisum sativum L.) were placed vertically in air of 91% relative humidity and 2 to 3 mm from the water-saturated porous tube placed horizontally, the roots responded hydrotropically and grew in a continuous arch along the circular surface of the tube. By contrast, normal gravitropic roots of `Alaska' pea initially showed a slight transient curvature toward the tube and then resumed vertical downward growth due to gravitropism. Thus, in microgravity, normal gravitropic roots could respond to a moisture gradient as strongly as the agravitropic roots used in this study. Hydrotropism should be considered a significant factor responsible for orientation of root growth in microgravity.

Free access