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Abstract

Activities of the acidic and basic peroxidases from tomato fruit (Lycopersicon esculentum Mill. cv. Flora Dade) were determined at six ripening stages, from green to red-ripe fruits. Both the acidic and basic peroxidases reached a maximum during the climacteric, at the pink stage, but the relative increase in basic peroxidase activity was much more pronounced. Changes in the peroxidase, IAA oxidase, and ACC oxidase activities of the basic peroxidases paralleled the changes in ethylene production. However, in the presence of calcium, the degree of activation of peroxidase was constant throughout ripening, whereas the IAA and ACC oxidase activities of the basic peroxidases were only activated at the pink stage.

Open Access

`South Bay' lettuce (Lactuca sativa L.) seedlings were grown in a greenhouse during winter, spring, and fall to investigate the effect of cell size and medium compression on transplant quality and yield. Four Speedling planter flats (1.9-, 10.9-, 19.3-, 39.7-cm3 cells) and two medium compression levels [noncompressed and compressed (1.5 times in weight)] were tested. The two larger cell sizes and compression of the medium led to increased plant shoot growth. Conversely, root weight ratio [RWR = (final root dry weight ÷ final total dry weight + initial root dry weight ÷ initial total dry weight) ÷ 2] was highest with the smaller cells without medium compression. Lettuce transplants were field-grown on sand and muck soils. The larger cells delayed harvest by >2 weeks for plants grown on muck soil, but yield was unaffected. When grown on sandy soil, earliness was enhanced from plants grown in 19- and 40-cm3 cells, but head weights were not affected in the spring planting. In fall, heads were heavier for plants grown in 11-, 19-, or 40-cm3 cells compared with those from 2-cm3 cells. On sandy soil, harvest was delayed 13 days in spring and 16 days in fall for plants grown in the smallest cell size. Using the two smaller cell sizes saved medium and space in the greenhouse and increased the root growth ratio, but it led to reduced plant growth compared to using the bigger cells. Yield and earliness were more related to season and soil type than to transplant quality. On sandy soil, plants grown in 2- and 11-cm3 cells matured later, and yield was significantly decreased (8.6%) in fall by using plants from the 2-cm3 cells compared to the other sizes. From our results, compressing the medium in the cells was not justified because it is more costly and did not benefit yield in the field.

Free access

Cell size and media density can modify plant quality of greenhouse grown transplants through variation in light competition among plants, water and nutrient retention and root growth volumes required to fill the cells Thus, `South Bay' lettuce (Lactuga sativa L.) seedlings were grown in the greenhouse during different seasons to investigate the effect of different cell size and media packing density on transplant quality and yield for lettuce grown on sand and muck soils at different latitudes. Four Speedling flat cell sizes (882, 392, 242, 124 cells/flat) and two media packing densities (unpacked and packed - 1.5 times in weight) were tested in all the trials. Few seedling data parameters had an interaction between cell size and media density at transplanting. The larger cell size (242, 124 cells/flat) and greater media density led to increase leaf area, leaf length, shoot and total dry weight, RGR and LWR Conversely, RWR and the root:shoot ratio had the opposite trend, reaching the greater values with smaller cell size and less media density. High root growth can improve the pulling of the plants from the tray at transplanting and quicker establishment in the field. The treatments did not affect yield of plants grown on organic soil. When plants were grown on sandy soil head weights were greater from plants grown in 392, 242, or 124 cells/flat compared to 882 cells/flat.

Free access

The objectives of this study were to evaluate the risks and benefits of using artificial wetland-treated waters to irrigate tomato plants (Lycopersicom esculentum) and the potential for suppression of Pythium ultimum. The experiment was conducted in a greenhouse using tap water (control) and treated waters coming from three types of horizontal subsurface flow artificial wetlands filled with pozzolana and implanted with common cattail (Typha latifolia). Wetland units contained either a simple [artificial wetland with sucrose (AWS)] or complex [artificial wetland with compost (AWC)] carbon source or no [artificial wetland with no carbon (AW)] additional carbon source. A complete randomized split-block design comparing root sensitivity to root rot (inoculated and uninoculated plants) in main plots and four nutrient solutions [1) control, 2) treated water from AWS, 3) treated water from AWC, and 4) treated water from AW] in subplots was used in six replications. Tomato plants were inoculated with P. ultimum twice during the experimental period. The use of treated waters reduced the in vivo root Pythium population by 84% and 100% when the treated waters were from AWS and AWC, respectively. In vitro trials showed that sterilization or membrane filtration (0.2 μm) of treated waters significantly reduced the potential for suppression of P. ultimum, suggesting that microbial activity played an important role. On the other hand, all AW-treated waters had a negative effect on root development of uninoculated young tomato plants. Root dry weights of plants irrigated with treated waters was 56% lower than in control plants, while their shoot:root ratio was two times higher for plants irrigated with treated waters. The inoculated and AWC-treated water treatments also reduced the Fv:Fm ratio of dark-adapted leaves, representing the maximum quantum efficiency of photosystem II. Organic compounds present in treated waters, expressed as total and dissolved organic compounds, may have affected tomato root development.

Full access

Helianthus verticillatus Small (whorled sunflower) is a federally endangered plant species found only in the southeastern United States that has potential horticultural value. Evidence suggests that H. verticillatus is self-incompatible and reliant on insect pollination for seed production. However, the identity of probable pollinators is unknown. Floral visitors were collected and identified during Sept. 2017 and Sept. 2018. Thirty-six species of visitors, including 25 hymenopterans, 7 dipterans, 2 lepidopterans, and 2 other insect species, were captured during 7 collection days at a site in Georgia (1 day) and 2 locations in Tennessee (6 days). Within a collection day (0745–1815 hr), there were either five or six discrete half-hour collection periods when insects were captured. Insect visitor activity peaked during the 1145–1215 and 1345–1415 hr periods, and activity was least during the 0745–0845 and 0945–1015 hr periods at all three locations. Visitors were identified by genus and/or species with morphological keys and sequences of the cox-1 mitochondrial gene. The most frequent visitors at all sites were Bombus spp. (bumblebees); Ceratina calcarata (a small carpenter bee species) and members of the halictid bee tribe Augochlorini were the second and third most common visitors at the two Tennessee locations. Helianthus pollen on visitors was identified by microscopic observations and via direct polymerase chain reaction of DNA using Helianthus-specific microsatellites primers. Pollen grains were collected from the most frequent visitors and Apis mellifera (honeybee) and counted using a hemocytometer. Based on the frequency of the insects collected across the three sites and on the mean number of pollen grains carried on the body of the insects, Bombus spp., Halictus ligatus (sweat bee), Agapostemon spp., and Lasioglossum/Dialictus spp., collectively, are the most probable primary pollinators of H. verticillatus.

Open Access

Battery-powered autonomous mowers are designed to reduce the need of labor for lawn mowing compared with traditional endothermic engine mowers and at the same time to abate local emissions and noise. The aim of this research was to compare autonomous mower with traditional rotary mower on a tall fescue (Festuca arundinacea) lawn under different nitrogen (N) rates. A two-way factor experimental design with three replications was adopted. In the study, four N rates (0, 50, 100, and 150 kg·ha−1) and two mowing systems (autonomous mower vs. gasoline-powered walk-behind rotary mower equipped for mulching) were used. As expected, N fertilization increased turf quality. At the end of the trial, the autonomous mower increased turf density (3.2 shoots/cm2) compared with the rotary mower (2.1 shoots/cm2) and decreased average leaf width (2.1 mm) compared with the rotary mower (2.7 mm). Increased density and decreased leaf width with autonomous mowing yielded higher quality turf (7.3) compared with the rotary mower (6.4) and a lower weed incidence (6% and 9% cover for autonomous mower and rotary mower, respectively). Disease incidence and mowing quality were unaffected by the mowing system. The autonomous mower working time was set to 10 hours per day (≈7.8 hours for mowing and 2.2 hours for recharging) for a surface of 1296 m2. The traditional rotary mower working time for the same surface was 1.02 hours per week. The estimated primary energy consumption for autonomous mower was about 4.80 kWh/week compared with 12.60 kWh/week for gasoline-powered rotary mowing. Based on turf quality aspects and energy consumption, the use of autonomous mowers could be a promising alternative to traditional mowers.

Free access