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  • Author or Editor: Dennis B. McConnell x
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Abstract

Succinic acid 2,2-dimethyl hydrazide (Alar) was applied as 3 weekly foliar sprays at concentrations of 0, 1000, and 2000 ppm to ‘Sovereign’, an Fj cultivar of Tagetes erecta L., grown in a complete nutrient supply under long and short day photoperiods. Plants were sampled for anatomical study one week later. Treated plants grown under long days had thicker leaves and a larger root diameter. In short days, the capitula of treated plants were one-half the size of the untreated ones. The amount of phloem fibers in treated plants was less and cortical and pith cells were shorter in both photoperiods. Alar affected cell wall formation and the phloem fibers in the stems were thinner walled and less sclerified.

Open Access

Abstract

Succinic acid 2, 2-dimethylhydrazide (Alar) was applied as a foliar spray to ‘Sovereign’, an F1 cultivar of Tagetes erecta L., grown in a complete nutrient solution. Alar was applied weekly as a foliar spray at concn of 500, 1000, and 2000 ppm to plants grown under both short and long days. Short day control plants were shorter, flowered earlier, and had shorter leaves than the long day control plants. In each photoperiod, all plants treated with Alar were significantly shorter than the controls because of shorter in tern odes. Dry wt of the tops of treated plants were significantly less than the controls, but the dry wt of the roots were not significantly different. Leaf length and no. of nodes were not affected by the different concn. In short days, Alar delayed flowering up to 8 days, but did not affect the size of the terminal flower.

Open Access

Dracaena sanderana `Ribbon' plants were grown under 47%, 63%, 80%, and 91% shade. After 15 weeks of growth, plants exhibited marked changes in various morphological features. In order to precisely compare leaves of plants grown under different light levels the Plastochron Index (PI) of Erickson and Mickelini (1957) was used. The plastochron was defined in terms of leaf length. Various leaf morphological characteristics were examined and correlated with 1) actual leaf numbers, and 2) with leaf developmental age. A comparison between the two methods 1) and 2) revealed that overall trends displayed by leaves with a Leaf Plastochron Index (LPI) from 12 to 2 were similar to the same trends linked to actual leaf numbers. However, leaves with LPIs lower than 2 showed that under 80% and 91% shade these leaves had higher values for all studied parameters. Comparable leaves of plants in 91% shade had consistently higher values of the leaf parameters compared to plants in other shade treatments. The use of the PI enabled us to accurately compare morphological differences between plants grown under diverse light conditions.

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Detection of cuticular crystals in the 14 species of Dracaena examined indicated that they are probably ubiquitous throughout the genus and may permit rapid separation of dracaenas from plants with similar leaves such as the cordylines (Cordyline sp.). Dracaena species of the dragon tree group deposit the greatest quantity of uniformly small cuticular crystals. However, the distinction between individual species within this grouping, based solely on crystal numbers and size, is not sufficient for taxonomic separation. All other species of Dracaena studied did display species-specific quantities and sizes of cuticular crystals. This, in combination with characteristics of the leaf epidermis, could serve as part of a taxonomic key to the genus.

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The effect of 0, 3, and 7 mm Ca2+ on the allocation and deposition of Ca2+ into intracellular and sub-cuticular periplasmic calcium oxalate (CO) crystals was examined in leaf primordia of rooted cuttings of Dracaena sanderiana Hort. Sander ex M.T. Mast. Crystal development was monitored in two types of cuttings, those rooted in deionized water for 18 months and those rooted in Metro Mix 500 for 6 weeks. Response differed remarkably depending on the type of cutting. Cuttings rooted in deionized water deposited sub-cuticular crystals at the expense of intracellular crystals (raphides). The number of sub-cuticular crystals in leaf primordia of cuttings rooted in deionized water grown in solutions supplemented with either 0, 3, or 7 mm Ca2+ was similar, but crystals were considerably smaller in plants grown in 0 mm Ca2+. Sub-cuticular crystals appeared developmentally earlier in leaf primordia of all cuttings grown in either 3 mm or 7 mm Ca2+ than in cuttings rooted in deionized water grown in 0 mm Ca2+. This finding supports the premise that deposition of sub-cuticular crystals is modulated by Ca2+ levels and could be induced at an earlier ontogenetical stage by raising rhizospheric Ca2+ levels or delayed by lowering rhizospheric Ca2+ levels. The total number of sub-cuticular crystals per epidermal cell did not differ significantly between treatments implying that crystal nucleation sites are predetermined and finite in number. In contrast, the formation of intracellular raphides was highly variable and depended on Ca2+ concentrations. In terms of Ca2+ prioritization, sub-cuticular CO crystals took precedence over intracellular CO raphides.

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Effects of four shade levels (47%, 63%, 80%, and 91%) on growth of D. sanderana `Ribbon' were evaluated. D. sanderana exhibited morphological and anatomical plasticity manifested in differences in all growth parameters examined. Plant growth rate was significantly influenced by the light levels. Under 63% and 80% shade plants grew faster and achieved greater biomass than plants grown under 475% and 91% shade. Leaf variegation was affected by the shade level. Plants grown in 47% and 63% shade had less total variegation than plants grown in 80% and 91% shade. Leaf thickness was greater in plants grown under higher light levels. Marginal leaf growth was suppressed in plants grown in 47% and 63% shade, thus reducing the width of the achlorophyllous margins. The reverse occurred in leaves of plants grown in 80% and 91% shade. The change in variegation pattern occurred very early in leaf ontogeny—during lamina formation and expansion. This change was attributed to differences in relative contribution of the three shoot apical layers under different light conditions. Thus, Dracaena sanderana `Ribbon' when grown in the southeastern United States is shade obligate, with an optimum light intensity level of less than 53% of full sunlight.

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Environmental Horticulture-undergraduate student enrollment at the University of Florida (UF) Gainesville campus decreased from 88 students in 1980/81 to 34 students in 1989/90. In 1983/84 a resident instruction program in Environmental Horticulture for placebound students was initiated by UF at the Ft. Lauderdale Research and Education Center. Enrollment rapidly increased from 6 students in 1984 to 67 students in 1989, with an average student credit load of 3.5 credits per semester. In 1990/91 increased student recruiting efforts were made with a common undergraduate handbook, recruiting brochure, and guides for academic program specializations developed to serve both locations. These efforts and others have increased enrollment at both sites. Currently there are 73 students in the Environmental Horticulture program at Gainesville and 87 students at Ft. Lauderdale. Students may begin their academic program at one location and transfer to the other site to complete their undergraduate requirements for the Bachelor of Science degree. A Bachelor of Science program in Environmental Horticulture will be initiated in the fall of 1994 in Milton, Florida, a small community in northwest Florida.

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Three foliage plants, Dracaena fragrans, Peperomia obtusifolia and Schefflera arboricola were grown in 24 different mixes. Potting mixes were formulated using yard waste compost from two sources, a commercial mix (Metro 300) and a prepared mix (peat: pine bark sand). All potting mixes produced acceptable plants with no phytotoxicity associated with any mix. Only minor differences were discerned in the growth rate of P. obtusifolia and S. arboricola.

The growth rate of D. fragrans showed the greatest response to potting mix formulations. Plants in a standard potting mix (P/PB/S) used in the industry for D. fragrans grew slower than plants in many of the mixes containing various fractions of yard waste compost. Chemical and physical properties of the potting mixes used showed physical properties had the greatest variability. Overall, the best growth for all 3 plants was in a potting mix composed of 87.5% Metro 300/12. 5% YWC#1 and worst growth was in YWC#2 (100% composted (live oak leaves).

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Tissue-culturedexplantsofDieffenbachiamaculate`Exotic Perfection', D.`Snow Flake', and D. × `Tropic Breeze' were grown on ebb-and-flow trays subirrigated with nitrogen (N) at 50, 200, or 800 mg·L-1 using a water-soluble fertilizer 17N–2.1P–15.7K for 10 weeks in a shaded greenhouse under a maximum photosynthetic photon flux density of 285 μmol·m-2·s-1. Plants were then transferred to interior rooms under a light level of 8 μmol·m-2·s-1. Samples of the midrib were taken from the first mature leaf of plants before being placed indoors and also from the first mature leaf of plants 8 months after growing indoors. Counts of calcium oxalate crystal idioblasts in cross-sections of the basal midrib using polarized light microscopy showed that the number of crystal idioblasts was higher in all three cultivars fertigated with 200 mg·L-1 N than those fertigated with either 50 or 800 mg·L-1 N. The number of crystal idioblasts in each cultivar grown under 8 μmol·m-2·s-1 was about 50% of the number detected when plants were grown under 285 μmol·m-2·s-1. `Snow Flake' had the highest number of crystal idioblasts with counts up to 60 per cross-section, whereas `Exotic Perfection' had the lowest with only 30 per cross-section. This study shows that in addition to cultivar differences, light intensity and N can significantly affect calcium crystal formation, and the highest number of crystal idioblasts occurred when Dieffenbachia cultivars were grown under optimum conditions.

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A simple and effective method for quantification of leaf variegation was developed. Using a digital camera or a scanner, the image of a variegated leaf was imported into a computer and saved to a file. Total pixels of the entire leaf area and total pixels of each color within the leaf were determined using an Adobe Photoshop graphics editor. Thus, the percentage of each color's total pixel count in relation to the total pixel count of the entire leaf was obtained. Total leaf area was measured through a leaf area meter; the exact area of this color was calculated in reference to the pixel percentage obtained from Photoshop. Using this method, variegated leaves of ‘Mary Ann’ aglaonema (Aglaonema x), ‘Ornate’ calathea (Calathea ornate), ‘Yellow Petra’ codiaeum (Codiaeum variegatum), ‘Florida Beauty’ dracaena (Dracaena surculosa), ‘Camille’ dieffenbachia (Dieffenbachia maculata), and ‘Triostar’ stromanthe (Stromanthe sanguinea) were quantified. After a brief training period, this method was used by five randomly selected individuals to quantify the variegation of the same set of leaves. The results were highly reproducible no matter who performed the quantification. This method, which the authors have chosen to call the quantification of leaf variegation (QLV) method, can be used for monitoring changes in colors and variegation patterns incited by abiotic and biotic stresses as well as quantifying differences in variegation patterns of plants developed in breeding programs.

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