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Photothermal ratio (PTR) is defined as the ratio of radiant energy (light) to thermal energy (temperature). The objective of this study was to quantify the effect of PTR during the vegetative (PTRv) and reproductive phase (PTRr) on finished plant quality of `Freedom' poinsettia. In Expt. I, plants were grown under 27 combinations of three temperatures, three daily light integrals (DLI), and three plant spacings from pinch to the onset of short-day flower induction and then moved to a common PTR until anthesis. In Expt. II, plants were grown under a common PTR during the vegetative stage and then assigned to nine combinations of one temperature, three DLIs, and three plant spacings after the onset of short-day flower induction. Both PTRr and PTRv affected final plant dry weight. All components of dry weight (total, stem, green leaf, and bract) responded in a linear way to PTRr and in a quadratic way to PTRv. Stem strength was more dependent on PTRv than PTRr. When PTRv increased from 0.02 to 0.06 mol/degree-day per plant, stem diameter increased about 24% while stem strength increased 75%. The size of bracts and cyathia was linearly correlated to PTRr, but not affected by PTRv. When PTRr increased from 0.02 to 0.06 mol/degree-day per plant, bract area, inflorescence diameter, and cyathia diameter increased 45%, 23%, and 44%, respectively.
A shade experiment for pruned coffee trees was conducted on Maui, Hawaii, in 1996. Nine-year-old `Guadalupe' trees were stumped at 70 cm above the ground, and three main verticals were allowed to remain on the main trunk. Each stumped tree was randomly selected and covered with shade cloth. The shade cloths were 30%, 50%, and 70% shade, and each shade structure had a length × width × height of 1.5 × 1.5 × 2.5 m. Data were collected in 1997. In general, the basal diameters of the verticals were similar in all treatments, as were the lengths of the verticals. The total number of laterals in the full-light treatment was slightly more than that of the other treatments. The numbers of flowering laterals were similar in all treatments. The numbers of fruit per tree in the full light, 30%, 50%, and 70% shade treatments were 1876, 3434, 2399, and 403, respectively. Fruit per flowering node was the best index relating to yield. Fruit per node was highest under 30% shade, followed by full light and 70% shade. At the beginning, fruit ripened faster in the full light treatment than in the other treatments, but at the end of September, fruit in 70% shade ripened slower than the other treatments. Therefore, after stumping, coffee trees grew best under 30% shade. For coffee, pruning under the field condition, stumping every other row of trees may be a satisfactory way to obtain the best yield in the future.
It is difficult to estimate the total leaf area of coffee plants with accuracy due to the large number of leaves and the high leaf density of the plant canopy. In 1996, on Maui, Hawaii, 98 leaves of various sizes were randomly collected for each of five cultivars of Coffea arabica L. The cultivars used were `Guadalupe', `Guatemalan', `Mokka', `Red Catuai', and `Yellow Caturra'. Leaf length, width, and area were measured. Seventy-five leaves were used to develop leaf area models, and the remaining leaves were used to test the accuracy of the models using a 1:1 line. We then developed leaf area devices (LADs), which were made of sheet plastic and shaped to resemble coffee leaves. There were three groups of areas in the leaf area devices, based on leaf sizes. Total leaf area (TLA) contained three components. Each component related to the mean leaf area (k) and the number of leaves (n) in that group. The model for the total leaf area was: TLA = k1n1 + k2n2 + k3n3, where k is a constant in each group. The estimation errors for the different cultivars ranged from 5.6% to 12.3% for 1-year-old plants (four cultivars) and from 1.9% to 7.8% for mature plants (five cultivars). By using the LADs and counting the number of leaves, we can obtain the total leaf area for coffee plants in the field.
Turfgrass is grown under a wide range of environmental conditions, especially light conditions. In residential and commercial applications, selecting the appropriate turfgrass depends, in part, upon its performance under differing light conditions. This study was conducted to determine the growth habits of four turfgrasses under different shade treatments. `Common Bermuda', `Tif dwarf Bermuda', `Seashore Paspalum', and `Z-3' were grown outdoors in pots. `Z-3' is an attractive new variety of turfgrass for residential lawns. Benches were covered with shade cloth to provide different shade conditions (0%, 30%, and 50% shading). Clippings were taken every 2 weeks and dried to determine growth. Turfgrass growth under the three shade treatments were significantly different. In the 0% and 30% shade treatments, `Common Bermuda' and `Seashore Paspalum' had similar growth with their dry weights being greater than that of `Tif dwarf Bermuda' and `Z-3'. Under 50% shade, `Seashore Paspalum' grew significantly greater than the other turfgrasses. `Common Bermuda' grew significantly less under 50% shade than under 0% and 30% shade. `Common Bermuda' does well on golf courses because of its fast growth and attractiveness. With its vigorous growth and shade tolerance, `Seashore Paspalum' can be used for residential lawns. `Z-3' turfgrass, a relatively new variety for residential lawns, shows slow growth but is desirable because of its tolerance to different shade conditions.
The objectives of this study were to quantify the effects of the radiant-to-thermal energy ratio (RRT) on poinsettia plant growth and development during the vegetative stage and develop a simple, mechanistic model for poinsettia quality control. Based on greenhouse experiments conducted with 27 treatment combinations; i.e., factorial combinations of three levels of constant temperature (19, 23, or 27°C), three levels of daily light integral (5, 10, or 20 mol/m2 per day), and three plant spacings (15 × 15, 22 × 22, or 30 × 30 cm), from pinch to the onset of short-day flower induction, the relationship between plant growth/development and light/temperature has been established. A model for poinsettia quality control was constructed using the computer software program STELLA II. The t-test shows that there were no significant differences between model predictions and actual observations for all considered plant characteristics; i.e., total, leaf and stem dry weight, leaf unfolding number, leaf area index, and leaf area. The simulation results confirm that RRT is an important parameter to describe potential plant quality in floral crop production.
The lettuce aphid, Nasonovia ribisnigri Mosley (Hemiptera: Aphididae), is a major insect pest of lettuce, Lactuca sativa L, in many commercial lettuce production areas around the world. Resistance to lettuce aphid biotype 0 (Nr:0) was first reported in Lactuca virosa L. accession IVT 280 and characterized as complete, i.e., virtually no aphids survived, and genetically dominant to partial resistance in L. virosa accession IVT 273. Complete and partial resistances to Nr:0 were conditioned by two alleles, Nr (complete resistance) and nr (partial resistance), but the genetic relationship to susceptibility was not reported. We previously reported two new potential sources of unique genes for resistance to Nr:0 in Lactuca serriola L. accession PI 491093 and L. virosa PI 274378. We report on the genetic and phenotypic nature of resistance to Nr:0 in these two wild lettuce accessions. Resistance to Nr:0 in PI 274378 is complete and allelic to complete resistance in IVT 280. Resistance to Nr:0 in PI 491093 was partial, recessive to complete resistance in ‘Barcelona’ that was derived from IVT 280, but dominant to susceptibility in ‘Salinas’. We propose the revised gene symbols for resistance to Nr:0: Nr:0C for complete resistance and Nr:0P for partial resistance, which was originally designated as nr but may now be regarded as the symbol for susceptibility to all strains of lettuce aphid. The dominance relationships among these three alleles are Nr:0C (in IVT 280, ‘Barcelona’) > Nr:0P (in PI 491093) > nr (in susceptible genotypes). Expression of partial resistance in PI 491093 was variable in controlled infestation tests, but in a naturally infested field test provided a potentially useful level of resistance to Nr:0. Partial resistance, where complete resistance has not been widely deployed, may either alone or as a component of integrated pest management delay or prevent emergence of genotypes that overcome complete resistance controlled by Nr:0C .
Abstract
Pedicel sections from the flowers of Easter lily (Lilium longiflorum Thunb.) were cultured on a modified Murashige-Skoog medium containing various concentrations of cytokinins and auxins. A combination of BAP (5 μM) and NAA (2 μM) resulted in the greatest number of adventitious buds on pedicel sections. A gradient in the formation of buds in the pedicel was observed, with the section nearest the receptacle forming the greatest number, especially when the section was placed upside-down on the culture medium. IAA (10 μM) and IBA (10 μM) were most effective in stimulating adventitious roots in vitro-derived shoots. This vegetative propagation technique provides a way of amplifying floral mutants of Easter lily. Chemical names used: benzylamipropurine (BAP); 1-naphthaleneacetic acid (NAA); 1H-indole-3-acetic acid (IAA); and 1H-indole-3-butanoic acid (IBA).
Plant growth and development are driven by two forms of energy: radiant and thermal. This study was undertaken to determine the effect of the ratio of radiant energy to thermal energy on plant quality of Euphorbia pulcherrima `Freedom'. Plants were grown under 27 combinations of temperature (thermal energy), light (radiant energy), and spacing, i.e., factorial combinations of three levels of constant temperature (19, 23, or 27°C:), three levels of daily light integral (5, 10, or 20 mol·m–2·d–1), and three levels of plant spacing (15 × 15, 22 × 22, or 30 × 30 cm), from pinch to the onset of short-day flower induction. Plants were treated for 450 degree-days (base temperature = 5°C) in Expt. 1 or 5 weeks in Expt. 2. The results showed that increasing radiant energy or decreasing average daily temperature during accumulation of 450 degree-days increased plant dry weight. When radiant and thermal energy were calculated into the ratio, plant dry weight increased linearly as the ratio increased Plants exposed to low light: levels and high temperatures, i.e., those at a low ratio, developed thin, weak stems. Higher radiant-to-thermal energy ratios produced thicker stems.
Four turfgrasses (Z-3, Seashore Paspalum, Common Bermuda, and Tif dwarf Bermuda) were grown outdoors in pots under different shade conditions (0%, 30%, and 50% shade) from August to December 1995. Dry weight of clippings taken every two weeks was determined. Turfgrass growth in the three shade treatments were significantly different, and the growth of the turfgrasses were highly significantly different. In the 0% and 30% shade treatments, Common Bermuda and Seashore Paspalum grew similarly, and their dry weights were significantly greater than those of Z-3 and Tif dwarf Bermuda. However, under 50% shade, only Seashore Paspalum grew significantly greater than the others. Comparing growth among the shade treatments for each turfgrass, we found no significantly differences. Only Common Bermuda grew significantly less under 50% shade than under 0% and 30% shade. Common Bermuda is good for golf courses because of its fast growth and attractiveness. Seashore Paspalum can be used for home lawns because of its vigorous growth and shade tolerance. Z-3 turfgrass, an attractive new variety for home lawns, despite its slow growth, is tolerant of different shade conditions.
Light (radiant energy) and temperature (thermal energy) affect quality of greenhouse crops. Radiant energy drives photosynthesis and, consequently, plant biomass accumulation. Thermal energy is the primary environmental factor driving developmental rate. The concept of a photothermal ratio (PTR), the ratio of radiant energy [moles of photosynthetic (400 to 700 nm) photons/m2] to thermal energy (degree-day), was proposed to describe the balance between plant growth and plant development in greenhouse crops. The objective of this study was to quantify the effect of PTR during vegetative (PTRv) or reproductive (PTRr) phases on finished plant quality of `Freedom' poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch). In Expt. 1, plants were grown under 27 combinations of three constant temperatures (19, 23, or 27 °C), three daily light integrals (DLIs) as measured by the number of photosynthetic (400 to 700 nm) photons (5, 10, or 20 mol·m-2·d-1), and three plant spacings (15 × 15, 22 × 22, or 30 × 30 cm) from pinch to the start of short-day flower induction, and then moved to a common PTR until anthesis. In Expt. 2, plants were grown under a common PTR during the vegetative stage and then moved to combinations of three DLIs (5, 10, or 15 mol·m-2·d-1) and three plant spacings (25 × 25, 30 × 30, or 35 × 35 cm) at a constant 20 °C from the start of short days until anthesis. Both PTRr and PTRv affected final plant dry weight (DW). All components of DW (total, stem, leaf, and bract) increased linearly as PTRr increased, and responded quadratically to PTRv, reaching a maximum when PTRv was 0.04 mol/degree-day per plant. Stem strength depended more on PTRv than PTRr. When PTRv increased from 0.02 to 0.06 mol/degree-day per plant, stem diameter increased ≈24%, while stem strength increased 75%. The size of bracts and cyathia increased linearly as PTRr increased, but was unaffected by PTRv. When PTRr increased from 0.02 to 0.06 mol/degree-day per plant, bract area, inflorescence diameter, and cyathia diameter increased 45%, 23%, and 44%, respectively.