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  • Author or Editor: B.V. Pennisi x
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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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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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In Georgia, horticulture is now the number two commodity in the state. The labor needs of the industry is increasing, however, enrollment in horticulture classes at UGA has been dropping. Most entry-level employees joining horticulture firms are completely without training or understanding of the industry, the type of work or the basic skills necessary to be functional. If horticulture was taught, it was by persons with Vo-Ag training in small engines, or animal husbandry etc. Students reported teachers had very little enthusiasm for the subject, no school facilities and that the school principle/administration had no vision for, or understanding of, horticulture. We are addressing this situation through an innovative partnership between Georgia High Schools, The Georgia Department of Education, and the University of Georgia. We can reverse the trend by training new and existing high school teachers by providing them a standardized floriculture curriculum and comprehensive training in greenhouse management, classroom teaching methods, industry awareness and a provide a long-term link to UGA. Our objective is to increase the number of students who are trained, motivated and willing to work in the field of horticulture as entry level workers. To do this we set about to standardize the course curriculum statewide, certify the high-school, faculty and administration for commitment and program continuity, Set up a model training greenhouse system at UGA, and conduct new teacher training at UGA through ALEC, and conduct postcertification training for teachers at UGA during the summer to upgrade skills, enthusiasm. The venture, including a model greenhouse at UGA, has been funded for over $100,000. The program currently has 218 Schools, 64 w/labs and greenhouses, 215 teachers and 25,049 students participating.

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In an effort to expand and improve the agriculture curriculum, the Georgia Department of Education set standards for new greenhouses to be built at high schools. These modern greenhouses are to serve as teaching facilities for new horticulture classes. However, current teachers had little or no background or experience in teaching greenhouse or nursery management courses. In response to the GDE needs, a summer workshop “Managing Crop Production and Equipment in the School Greenhouse” was held at CAES Griffin Campus and at Pike County High School. Faculty from UGA departments presented topics such as water quality, irrigation and crop nutrition, cultural guidelines for major floricultural crops, IPM, pesticide safety, and marketing, business planning and fund raising. Included in the program were numerous hands-on activities designed to cover the essential practical skills needed for a greenhouse employee—proper handling and planting of plugs, watering, calculating fertilizer rates, fertilizer injector maintenance and calibration, soil pH and fertility monitoring, scouting and pest identification, and proper pesticide handling and spraying techniques. Twenty-two teachers from schools with horticulture curriculum attended the training. The workshop evaluations indicated high satisfaction with the material presented. Teachers pointed out that the practical skills had not only been very useful but also the manner in which they were presented would be easily applicable to students. The knowledge acquired will be incorporated into the fall and spring curriculum. Through the effort of the floriculture specialist, a high-quality educational program was delivered to Georgia High School teachers, which in turn translate into attracting student into joining the growing ornamental horticulture industry.

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Detailed anatomical observations of the dorsal gland and its development in Ficus benjamina L. (Weeping Fig) leaves are reported. The dark spot on the abaxial surface of Ficus benjamina leaves is a normal morphological feature of the species. It is a highly specialized modified epidermal layer. An investigation of six commercially available cultivars revealed all possessed a glandular dorsal epidermis but not all developed a pigmented gland. The variability in gland thickness suggests that differences exist between cultivars. Based on histochemical tests, we propose that the term “phenolic gland” be substituted for the term “wax gland” found in the literature, as all tests indicated the presence of polyphenols in the glandular epithelium of F. benjamina leaves.

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We induced preferential allocation of Ca to two calcium oxalate (CO) sinks in immature leaf tissues of D. sanderiana: subepidermal extracellular deposits and intracellular raphides. Allocation was affected by exogenous Ca levels. Two groups of rooted cuttings were termed Ca-deficient and non-deficient. The first group consisted of cuttings that had been deprived of Ca for 18 months, and, the second, cuttings rooted under standard horticultural conditions. All plants were grown in liquid medium supplemented with 100 ppm of potassium nitrate and subjected to 0, 3, or 7mm Ca from calcium acetate. The most striking feature of Ca-deficient plants grown in 0 mm Ca was the absence of intracellular raphides in the leaf primordia. The largest number of intracellular raphides developed in Ca-deficient plants grown in 7 mm Ca. The number of extracellular crystals in Ca-deficient plants grown in Ca-supplemented solutions versus non-supplemented were similar, but crystals were considerably smaller in non-supplemented plants. Total number of extracellular crystals per epidermal cell did not differ significantly between plants in all treatments. This implies that nucleation sites are pre-determined and finite in number. In contrast, the number of intracellular raphides was highly variable. In terms of Ca prioritization, the extracellular crystals took precedence over intracellular raphides, and this was most obvious in Ca-deficient plants. The significance of this research is that the extracellular crystals represent Ca sinks with limited induction capacity compared to intracellular Ca sinks. Plants with genetic predisposition for intracellular CO crystal formation may be able to respond favorably to root environments with low Ca levels compared to species with limited capacity for intracellular CO deposition. Intracellular CO crystals, therefore, play an integral role in plant nutrition as Ca storage sinks.

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In 1975, the Environmental Horticulture Dept. initiated a work experience program. Students who work full time for an environmental firm of institution may register for ORH 4941 Practical Work Experience. Although ORH 4941 was not required, 241 students participated in the program during the 22 years when it was an elective course. In 1998, the departmental education committee changed the status of ORH 4941 from an elective to a required course. The objectives of this study were to determine if any differences have occurred since the status of the course has changed. The following were examined: 1) selected student characteristics (GPA, gender, age, etc.), 2) employing firms participating in the work experience program, and 3) required administrative procedures.

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Tissue culture plugs of Aglaonema `Cory', `Maria', and `Silver Queen' and Dieffenbachia `Panther', `Snowflake', and `Sport Lynn' were potted singly in 15-cm pots and grown in a shaded greenhouse under a photosynthetic irradiance (PI) of 100 mmol·m–2·s–1. Eight months after potting, 27 plants of each cultivar were placed in nine interior evaluation rooms under three different PI levels (three rooms per level): 4, 8, and 16 mmol·m–2·s–1. In addition, three plants of each cultivar were maintained in the original greenhouse for the duration of the experiment. Number of leaves, plant height and width were monitored monthly. Recently matured leaves were removed at 3-month intervals for 9 months for determination of fresh and dry weight, leaf area, and percentage leaf variegation. Variegated leaf area was assessed using digitized leaf images. Interior PI levels affected growth parameters, but the degree of response was cultivar-dependent. Smallest leaves developed on plants grown under 4 mmol·m–2·s–1 and largest leaves developed under 16 mmol·m–2·s–1. Leaf area of Dieffenbachia `Sport Lynn' showed the greatest response and Aglaonema `Maria' the least response to PI levels. Percentage leaf variegation of Dieffenbachia `Snowflake' was least affected and Dieffenbachia `Sport Lynn' was most affected by PI levels. Fresh leaf weight of unit area decreased as PI levels decreased from 16 to 4 mmol·m–2·s–1, however, the decrease in unit area was most pronounced in cultivars that maintained the highest quality ratings. Based on the results of this study, Aglaonema `Maria' and Dieffenbachia `Snowflake' had the most satisfactory interior performance within their respective genera.

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