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- Author or Editor: D. D. Davis x
Plugs of Zinnia elegans Jacq. `California Giant' and Tagetes erecta L. `Golden Climax' and `Grange Lady' were treated with foliar sprays of uniconazole solutions at 0, 5, 25, or 50 mg·liter-1 (spray volume = 120 ml·m-2). Ten days later individual plants were transplanted to OS-liter pots for evaluation of subsequent growth and flowering. All uniconazole treatments reduced height 10 days after application; the extent of reduction depended on uniconazole spray concentration. With zinnia, only the 50-mg·liter-1 foliar spray caused undesirable stunting for at least 1 month after transplanting. None of the uniconazole treatments affected time to anthesis for zinnia. With both marigold cultivars, all uniconazole treatments reduced growth the 2 weeks following transplanting. The highest concentration reduced marigold shoot growth during this period to 25% to 30% of untreated controls. Between 2 and 4 weeks after transplanting growth of all uniconazole-treated marigolds recovered to levels similar to the control. Time to anthesis was increased by the 50 mg·liter-1 treatment for both marigold cultivars. These results suggest that foliar sprays of uniconazole at 5 to 25 mg·liter-1 can control plug height during production without adversely affecting subsequent growth and flowering. with both zinnia and marigold, a single GA3 foliar spray of 100 mg·liter-1 at transplanting partially reversed the adverse post-production effects of the 50 mg·liter-1 uniconazole foliar spray.
Seedlings of 3 birch species were exposed to either 0.3, 0.6, 0.9, or 1.2 ppm SO2 for 1, 2, 3, or 4 hours. Stomatal conductance rate measurements of 10 plants were taken prior to and immediately following each exposure. The percentage of leaf tissue injured by SO2 was estimated 72 hours after exposure. Stomatal conductance rates of European white birch (Betula pendula Roth.) and yellow birch (B. lutea Michx. f.) increased after exposure to 0.3 ppm SO2 for 1 and 2 hours, and decreased in response to all other doses of SO2. Stomatal conductance rates of gray birch (B. populifolia Marsh.) increased only after exposure to 0.6 ppm SO2 for 1 and 3 hours and decreased in response to all other dosages. European white birch was slightly more susceptible to SO2than gray birch, whereas yellow birch was tolerant.
More than 1000 plants representing 15 species and/or cultivars of woody ornamentals were exposed to 0.25 ppm ozone for 8 hours at bi-weekly intervals throughout the 1973 growing season. A different set of plants were utilized in each bi-weekly exposure. Plants injured at this rate, in descending order of susceptibility, were Rhododendron obtusum Planch. ‘Hinodegiri’ (Hinodegiri Hiryu azalea), Rhododendron poukhanensis Leveille (Korean azalea), Ailanthus altissima Swingle (tree-of-heaven), Ulmus parvifolia Jacq. (Chinese elm), Philadelphus coronarius L. (sweet mock-orange), Viburnum setigerum Hance (tea viburnum), and Viburnum dilatatum Thunb. (linden viburnum). Plants resistant at this rate were Ilex crenata Thunb. ‘Hetzii’ (Hetz Japanese holly), Ilex opaca Ait. (staminate and pistillate American holly), Kalmia latifolia L. (mountain-aurel kalmia), Lingustrum amurense Carr. (amur privet), Nyssa sylvatica Marsh, (black gum), Taxus × media Rehd. ‘Densiformis’ (dense Anglojap yew), Taxus × media Rehd. ‘Hatfieldii’ (Hatfield Anglojap yew), and Tilia americana L. (American linden). The most common ozone symptom on the broadleaved plants was a tan or dark red to black stipple on the upper leaf surface. Premature defoliation occurred on susceptible plants. Plants were more susceptible to ozone in mid- to late summer than in early spring.
Pinto bean plants (Phaseolus vulgaris L. cv. Pinto 111) in the unifoliolate leaf stage were exposed for 3 hours to 0.8 ppm SO2, 0.25 ppm 03, or a mixture of the 2 pollutants at these concentrations at 15, 24, or 32° C. Foliage exposed to O3 alone developed adaxial stipple and leaves exposed to SO2 alone developed interveinal necrosis. The mixture of O3 and SO2 induced O3-type symptoms at 32° and SO2-type symptoms at 15°. Both symptom types were present at 24°. Some abaxial glazing or silvering was also induced by the mixture, and was most common at 15° and 24°. Ozone and SO2 each induced greater foliar injury at 15° or 32°, as compared to 24°. The mixture of O3 and SO2 induced greatest macroscopic foliar injury at 15°. The degree of adaxial vs abaxial leaf surface injury varied with temperature.
Nine conifer species, including 3 selections of Scotch pine, were exposed to SO2 dosages of 1310 µg/m3 (0.5 ppm) for 5 hours, 2620 µg/m3 (1.0 ppm) for 4 hours, or 5240 µg/m3 (2.0 ppm) for 2 hours. Seedlings in the cotyledon and primary needle stages were utilized throughout the study. Significant injury occurred only at the highest concentration. Pine species (Pinus spp) were more susceptible to SO2 than were spruce (Picea spp.), fir (Abies spp.) or Douglas-fir (Pseudotsuga sp.). The 3 Scotch pine selections and ponderosa pine were more susceptible than Austrian pine species. Balsam fir, Douglas-fir, Fraser fir, white fir, blue spruce, and white spruce were not injured.
Ten cultivars of azalea (Rhododendron sp.) were exposed to 0.30 ± 0.05 ppm ozone (590 ±100 μg/m3) for 8 hours at various times during the summer. ‘Louise Gable,’ ‘Delaware Valley White’ and ‘Rose Greeley’ were significantly more susceptible than were ‘Stewartstonian,’ ‘Fedora,’ ‘Orange Beauty,’ ‘Hino-crimson,’ ‘Hershey Pink,’ ‘Rosebud,’ and ‘Springfield Crimson.’ Neither rate of gas exchange nor stomatal frequency was correlated with degree of visible injury induced by ozone.
Postharvest pitting of citrus fruit is a recently defined peel disorder that is caused by high-temperature storage (>10°C) of waxed fruit. We examined the anatomy of pitted white grapefruit peel to improve our understanding of this disorder and assist in its diagnosis. Scanning, light, and transmission micrographs showed that postharvest pitting is characterized by the collapse of oil glands. Cells enveloping the oil glands are the cells of primary damage. Oil gland rupture may occur anywhere around the oil gland, but often occurs in regions farthest from the epidermal cells. Adjacent parenchyma cells are damaged as the oil spreads. Epidermal and hypodermal cells are often damaged during severe oil gland collapse. In contrast, chilling injury is characterized by the collapse of epidermal and hypodermal cells. Oil glands are affected only in severe cases of chilling injury. Oleocellosis (oil spotting) is often characterized by the collapse of epidermal and hypodermal cells, but cells enveloping the oil gland are typically not damaged. Physical damage is characterized by damage of epidermal cells, a wound periderm, and presence of secondary pathogens.
Indonesia is one of the most populated countries in the world and is rich in plant biodiversity. The country’s hot humid climate is conducive to the production of many tropical horticultural crops. There are many plant species indigenous to Indonesia that have potential as horticultural crops but which have not been fully evaluated and therefore remain underused. Many of these plants have market potential and may have value for human health and nutrition. Furthermore, horticulture has been identified as one of the priority areas for collaboration between U.S. and Indonesian universities and for Indonesian agricultural development. Accordingly, we are presently working with three Indonesian universities to facilitate agricultural development related to horticulture by: 1) strengthening their curriculum related to plant biodiversity; 2) conducting research aimed at identifying bioactive compounds in underused plants that may have benefit to human health; 3) establishing university-led outreach education programs that lead to a better understanding of plant biodiversity and use; and 4) fostering enterprise based on underused Indonesian plant species. Other untapped agricultural research and development opportunities exist in the postharvest handling of tropical fruits and vegetables. Overall, the climate for collaboration between U.S. and Indonesian academic institutions is quite favorable from both a political and a scientific perspective.
Yuzuhada is a Japanese term given to a fruit disorder which often occurs when certain cultivars of the oriental pear, Pyrus serotina are grafted onto seedlings of that species or of P. betulaefolia. A literal translation of the name, yuzuhada, is pomelo (citrus) skin disease because in severe cases, fruits of some varieties develop surface depressions similar to thick citrus rind. The disorder was described in 1928 by Mizuno (3), but it is practically unknown to American horticulturists. According to Hayashi (1), and Hayashi and Wakisaka (2), the symptoms of yuzuhada are similar to those of hard-end and black-end of Bartlett pear in that the fruits fail to soften normally and often manifest some darkening of the distal end near the calyx lobes. That these two disorders occur on the same rootstock species and that some of their manifestations appear to be similar suggest that a relationship might exist between the two disorders. This investigation dealing with stock influence on the scion variety was, therefore, undertaken to ascertain if there were any correlations between the potential of a rootstock to produce black- or hard-end of Bartlett and yuzuhada symptoms in varieties of P. serotina and two interspecific hybrids.
Seeds of moth bean (Vigna aconitifolia Jacqu. Marechal cv. Jaadia) were germinated in the presence of 0, 0.1, 1, or 2 μm 24-epibrassinolide (EBL). After 72 h, cotyledons were excised and the seedlings exposed to 22 or 48 °C for 90 min. At 48 °C EBL increased total electrolyte, K+, and sugar leakage relative to the untreated control. Following exposure to 48 °C, EBL-treated seedlings had higher malondialdehyde concentrations than controls indicating that EBL enhanced high temperature-induced lipid peroxidation. At 48 °C, EBL increased ascorbic acid oxidase activity and decreased superoxide dismutase activity relative to the control. Taken together, these data do not support the hypothesis that brassinosteroids confer thermotolerance to plants. On the contrary, EBL increased high temperature-induced damage and reduced the activity of some antioxidant systems that may protect against stress-induced cellular damage.