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- Author or Editor: Gary W. Stutte x
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July-plugged transplants of short-day cv. Strawberry Festival (Fragaria ×ananassa) flowered in October and November although they were grown under long photoperiods and warm temperatures (greater than 21 °C) in July and August. These unexpected results were attributed to a high plant density (320 transplants/m2) that provided continuous and heavy leaf cover, which eliminated red light (less than 700 nm) from reaching the crowns. This hypothesis was tested by illuminating crowns of transplants growing in 50-cell packs for 16 h·d−1 with red light-emitting diode lamps (maximum wavelength at 639 nm and 80% of output between 617 and 655 nm). Red light treatment caused a significant reduction in fall flowering. It is proposed that a high ratio of far-red light to visible light reaching the crown will play a role in floral bud induction, possibly as early as mid-August. Transplants of some short-day cultivars started as plug plants in early July have the capacity to flower and fruit in the fall and the next spring, enabling growers in the mid-Atlantic coast region to obtain two harvests within 1 year from a single planting.
Ethylene production by 10 or 20 m2 stands of wheat, soybean, lettuce, potato, and tomato was monitored throughout growth and development in an atmospherically closed plant chamber. Chamber ethylene levels varied among species and rose during periods of canopy expansion and rapid growth for all species. Following this, ethylene levels either declined during seed fill and maturation for wheat and soybean, or remained relatively constant for potato and tomato (during flowering and early fruit development). Lettuce plants were harvested during rapid growth and peak ethylene production. Chamber ethylene levels increased rapidly during tomato ripening, reaching concentrations about 10 times that measured during vegetative growth. The highest ethylene production rates during vegetative growth ranged from 1.6 to 2.5 nmol·m-2·d-1 during rapid growth of lettuce and wheat stands, or about 0.3 to 0.5 nmol·g-1 fresh weight per hour. Estimates of stand ethylene production during tomato ripening showed that rates reached 43 nmol·m-2·d-1 in one study and 93 nmol·m-2·d-1 in a second study with higher lighting, or about 50× that of the rate during vegetative growth of tomato. In a related test with potato, the photoperiod was extended from 12 to 24 hours (continuous light) at 58 days after planting (to increase tuber yield), but this change in the environment caused a sharp increase in ethylene production from the basal rate of 0.4 to 6.2 nmol·m-2·d-1. Following this, the photoperiod was changed back to 12 h at 61 days and ethylene levels decreased. The results suggest three separate categories of ethylene production were observed with whole stands of plants: 1) production during rapid vegetative growth, 2) production during climacteric fruit ripening, and 3) production from environmental stress.
Accumulation of glycinebetaine occurs in Chenopodiaceae members and is thought to assist in osmotic adjustment and protect cytoplasm from sodium toxicity. Red beet has an ability to tolerate high tissue sodium levels, which may result in increased glycinebetaine production. To test this hypothesis, two cultivars of red beet ['Scarlet Supreme' (SS) and `Ruby Queen' (RQ)] were grown under nonsaline (4.75 mM Na) and saline (54.75 mM Na) conditions in a recirculating hydroponic system for 42 days at elevated CO2 (1200 μmol•mol-1) in a growth chamber. Leaf glycinebetaine level, relative water content, and osmotic potential were measured at weekly intervals. Leaf glycinebetaine levels increased with plant age and reached a maximum of 67 μmol•g-1 dw under nonsaline and 101 μmol•g-1 dry weight (dw) under saline conditions at 42 days in SS; in RQ, the glycinebetaine levels reached a maximum of 91 μmol•g-1 dw under nonsaline and 121 μmol•g-1 dw under saline conditions by 26 days. The mean glycinebetaine levels were increased over two-thirds under saline conditions in both the cultivars. RQ accumulated significantly higher (37% more under nonsaline, and 46% more under salinity) glycinebetaine than SS. The turgid leaf osmotic potential of RQ was consistently higher than SS under nonsaline (2.23 MPa in RQ vs. 1.82 MPa in SS) and saline (2.48 MPa in RQ vs. 2.02 MPa in SS) conditions. The results indicate that higher glycinebetaine levels in the leaf could result in better osmotic adjustment, and glycinebetaine accumulation in red beet can vary among cultivars and is strongly affected by external salinity.
Microcuttings of three western black cherry (Prunus serotina var. virens Ehrh.) phenotypes obtained from seedling trees with profuse or scant root systems were grown in two container sizes to examine the early effects of root constraint. Because manual methods to estimate root length and other characteristics are time consuming and subjective, an image analysis hardware and software system (image capture and analysis system) was used to classify and measure the roots. There was a significant effect of clone on fine-root surface area, coarse: fine root ratio, and root dry weight (P ≤ 0.05), but root characteristics (profuse or scant root development) of the parent material were absent in the vegetative propagules from these lines. Container size had no significant effect on coarse- or fine-root surface area but did reduce coarse: fine root ratio (P ≤ 0.05). A threshold effect of container size on root dry weight was detected (P ≤ 0.1).
The development of a crop production system that can be used on the International Space Station, long-duration transit missions, and lunar or Mars habitats, has been a part of NASA's Advanced Life Support (ALS) research efforts. Crops that can be grown under environmental conditions that might be encountered in the open cabin of a space vehicle would be an advantageous choice. The production efficiency of the system would be enhanced by growing these crops in a mixed-crop arrangement. This would also increase the variety of fresh foods available for the crew's dietary supplementation. Three candidate ALS salad crops, radish (Raphanus sativus L. cv. Cherry Bomb II), lettuce (Lactuca sativa L. cv. Flandria), and bunching onion (Allium fistulosum L. cv. Kinka) were grown hydroponically as either monoculture (control) or mixed-crop within a walk-in growth chamber with baseline environments maintained at 22 °C, 50% RH, 17.2 mol·m-2·d-1 light intensity and a 16-h light/8-h dark photoperiod under cool-white fluorescent lamps. Tests were carried out at three different CO2 concentrations: 400, 1200, and 4000 μmol·mol-1. Weekly time-course harvests were taken over 28 days of growth, and fresh mass, dry mass, and harvest index were determined. Results showed that none of the species experienced negative effects when grown together under mixed-crop conditions compared to monoculture growth conditions under the range of environmental conditions tested.
The effects of using mixed cropping strategies for reducing overall mass and increasing system efficiency was examined as part of NASA's mission to study minimally-processed or “salad” crops as dietary supplements on long-duration space missions. To test interspecific compatibility, radish (Raphanus sativus L. cv. Cherry Bomb II), lettuce (Lactuca sativa L. cv. Flandria), and bunching onion (Allium fistulosum L. cv. Kinka) were grown hydroponically as either monoculture (control) or mixed-crop within a walk-in growth chamber maintained at 25 °C, 50% relative humidity, 300 μmol·m-2·s-1 PPF, and a 16-h light/8-h dark photoperiod under cool-white fluorescent lamps. Weekly time-course harvests were taken over 28 days of growth. Results showed that none of the species showed any negative growth effects when grown together under mixed-crop compared to monoculture growth conditions. However, radish showed significant increases in edible mass when grown under mixed-crop compared to monoculture conditions. The observed increases in growth are likely attributable to increased light interception due to a decreased guard row effect as well as a faster canopy development for radish.