Variegated Dracaena sanderana plants were grown under 47%, 63%, 80%, and 91% shade cloth. Prior to that, plants were grown under uniform light levels in a greenhouse. Morphological changes which manifested the adaptation to different light levels were not evident until all four leaves present in the apical whorl had expanded. Changes first appeared in a leaf which was 5-15 mm long when plants were placed under the different shade levels. The changes were recognized as alteration in the amount of leaf variegation which gradually changed as new leaves unfolded. After development of four leaves no further morphological changes were apparent. The first `transition' leaf had variegation similar to the preceding leaf and the last `transition' leaf had variegation comparable to the next successive leaf. The amount of variegation was quantified and the changes under different light levels determined. The use of a variegated plant enabled us to readily observe the morphological changes related to light adaptation and showed that a plant is an integrated system which adapts to altered environment over an extended period of time.
Svoboda V. Pennisi and Dennis McConnell
Dennis B. McConnell and Wayne H. Smith
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).
Dennis B. McConnell and George F. Fitzpatrick
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.
Jennifer Campbell Bradley, Dennis McConnell and Tammy Kohlleppel
Attracting new students into traditional agriculture programs has become increasingly difficult. The idea of offering a course as a means for introducing students to agriculture is a concept with popular appeal. As a recruiting effort, and as a method of introducing students to horticulture, the Environmental Horticulture Dept. at the Univ. of Florida designed a one-credit course for non-majors. The course was structured such that a broad understanding of horticulture, including production, landscaping, and floriculture, would be emphasized. The intent was to develop a course somewhat similar to an entry-level course, but incorporating a more enjoyable, practical, hands-on approach. ORH 1030 Plants, Gardens, and You was offered for the first time in summer 1997. It is now offered every semester. The course has one faculty assigned each semester and various other faculty members, including teaching, research, and extension specialists who participate as “guest lecturers”. Student response to ORH 1030 has been favorable, ratings are high and enrollment in the course has continued to rise from 30 to our current cap of 100. As a means of ensuring that we are meeting the needs of our students and to aid in targeting potential students, a survey was administered in Spring 2000. Students enrolled in the course were surveyed at the beginning and the end of the semester to gain insight into student demographics, horticulture background and experience, reasons for enrollment in the class, attitude toward horticulture and overall interest in horticulture. Findings will be discussed in addition to information and suggestions for successfully establishing a similar course in other horticulture departments.
Svoboda V. Vladimirov and Dennis B. McConnell
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.
Svoboda V. Pennisi and Dennis B. McConnell
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.
Svoboda V. Pennisi and Dennis B. McConnell
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.
Svoboda V. Pennisi and Dennis B. McConnell
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.
Hui Cao, Jianjun Chen and Dennis B. McConnell
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.
Hui Cao, Hui Cao, Dennis B. McConnell and Jianjun Chen*
The irritant effect of Dieffenbachia sap is attributed to protelytic enxymes but calcium oxalate crystals are considered to puncture cells and allow enzyme entrance. To date, no detailed study of the location, type, or frequency of calcium oxalate crystals in Dieffenbachia species or cultivars has been undertaken. To do so, three uniform tissue culture plantlets of Dieffenbachia `Carina',`Rebecca' or `Star Bright' were transpanted into 15 cm pots, grown in a shaded greenhouse under 385 μmol·m-2·s-1 and fertigated with 20 N-8.7 P-16.6 K water-soluble fertilizer at N concentrations of 200 mg·L-1 twice weekly. Ten weeks later, samples of stem, root, and leaves were taken from 4 pots of each cultivar to determine the distribution and type of calcuium oxalate crystals in each plant organ via polarized light microscopy. Two types of calcium oxlate crystals, raphides and druses, were found in the stem, leaves and roots. Druse density increased as leaves andd stems matured while the number of raphide idioblasts remained relatively constant. Crystal density was highest at lateral initation sites of buds and roots. Significant differences were found in crystal density among cultivars even though `Carina' and `Star Bright' are sports selected from `Camille'. This suggests that reduction of calcium oxalate density of Dieffenbachia cultivars is possible through breeding.