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  • Author or Editor: Richard Craig x
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Undergraduate students teach laboratory sessions in the plant systematics course at The Pennsylvania State University. To assess student-taught laboratory sessions, surveys were administered to student instructors and students enrolled in the course. Benefits to student instructors included increased technical knowledge, new perspectives on teaching methodologies, and acquiring a positive item to add to résumés. Student instructors also practiced leadership skills. Enrolled students generally assessed the laboratory sessions favorably. Organization and planning were vital to the success of this teaching method. This teaching method also required increased departmental funding relative to other courses.

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Interspecific hybrids of Exacum species (Gentianaceae) endemic to Sri Lanka possess excellent qualities for domestication as a new floriculture crop. The exact mode of floral induction and development responses are unknown, impeding the introduction of this potential crop. The interspecific hybrids evaluated are the result of controlled cross pollinations of E. macranthum. Arn. ex Griseb., E. trinervium (L.) Druce ssp. trinervium, and E. trinervium ssp. ritigalensis. (Willis) Cramer. The hybrids exhibit great genetic variability for horticultural traits. In addition, two growth and flowering patterns exist within the Penn State germplasm. Continuous-flowering genotypes flower throughout the year but more profusely and rapidly under late spring and summer conditions. In contrast, periodic-flowering genotypes exhibit two distinct seasonal habits. Under winter conditions, these accessions have a rosetted habit, much secondary branching, and few or no flowers. In summer conditions, they break their apical dominance, bolt, and produce flowers. As members of the Gentianaceae, Exacum hybrids produce an elegant blue flower with a striking yellow eye and bottle-shaped anthers. We evaluated the growth and flowering responses of Exacum interspecific hybrid accessions to photoperiod and irradiance. Accessions were evaluated under greenhouse conditions for floral production, rate of floral development, and growth characteristics. For the 20 accessions evaluated, supplemental irradiance under winter conditions resulted in greater floral production and much greater shoot and root mass accumulation. Little height and branching response occurred with supplemental irradiance. Of the 15 accessions evaluated under four photoperiod regimes, flowering and growth responses to photoperiod occurred under summer conditions but not in winter. An interaction among season, accession, and photoperiod revealed the complexity of Exacum germplasm and environmental responses.

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Botrytis cinerea is an economically important fungal pathogen of Pelargonium species. We are currently studying this plant–pathogen interaction to identify mechanisms of host resistance. Our ultimate objective is to develop commercial Pelargonium genotypes with enhanced resistance to this pathogen. Though all stages of production may be affected by this pathogen, we are investigating foliar and floral resistance of mature plants. Through simple assays, over 200 genotypes have been evaluated for foliar resistance, and more than 100 genotypes have been evaluated for floral resistance. Resistant and susceptible control genotypes have been identified for diploid and tetraploid P. ×hortorum and P. peltatum; these genotypes are being investigated to elucidate mechanisms of resistance. The diploid ivy accession 86-23-1 and the tetraploid zonal geranium `Fox' have the greatest foliar resistance among the genotypes evaluated. The diploid P. ×hortorum `Ben Franklin' has the greatest floral resistance among the evaluated genotypes. Foliar and floral resistance appear to be inherited as separate traits. Foliar resistance is manifested as a two day delay in symptom expression when compared to susceptible genotypes. Foliar resistant accession 86-23-1 has a cuticle with 150% the mass of other Pelargonium genotypes. This difference may be responsible for the observed resistance. Cuticle mass does not appear to be important in floral resistance.

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Nine cultivars of Pelargonium ×domesticum L.H. Bailey were evaluated for the effect of daily light integral on floral initiation. Plants were grown at four daily light integrals: 5, 10, 15, or 20 mol·m-2·d-1 for a 16-hour photoperiod in environmental growth chambers at constant 15.5 °C. Meristems were examined at 50 mol·m-2 intervals for morphological changes associated with floral initiation. Two phenotypes were identified, cultivars with an association between floral initiation and cumulative irradiance and those with association between floral initiation and chronological time. Genotypic variation was observed among the irradiance-associated phenotypes.

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Abstract

M2 progenies from geranium (Pelargorium X hortorum L.H. Bailey), which had been irradiated with 1, 2, and 3 krads of acute gamma radiation, were evaluated for stem and branch length and number of leaves and branches. After several weeks, the progenies from plants irradiated with 2 and 3 krads were significantly shorter than the controls. Progenies treated with 3 krads were 21% shorter and exhibited a 30% reduction in branch length compared to the controls at the termination of the experiment. These effects were similar to those observed in the M1 generation. Leaf and branch number did not differ significantly among progenies of the irradiated plants. It is suggested that gamma radiation induced changes in endogenous levels of GA in the M1 plants, and these changes were transmitted to the M2 progenies.

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Abstract

Seeds of Pelargonium × hortorum cv. ‘Carefree Deep Salmon’ were given 1, 2, or 3 krad of acute gamma radiation to determine the influence on germination, plant morphology and growth. Percent germination was stimulated by 1 krad and inhibited by 3 krad compared to the control. Plant height and branch length were initially greater for irradiated plants, but the controls eventually grew significantly taller and had greater branch length than plants irradiated with 2 and 3 krads. The growth differential appeared to reflect differences in internode elongation and it is suggested that gamma irradiation may have altered the gibberellin status of the plants. Similar effects were noted for leaf and branch number; however, only the 3 krad dose caused a significant reduction in these parameters.

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Abstract

Morphological examination of the vegetative bud of American holly, Ilex opaca Ait., shows it to consist of an apical meristem surrounded by leaf primordia and these in turn by fleshy cataphyls (bud scales). With expansion of the bud into a shoot, flower buds are initiated in the axils of cataphyls and a few leaf primordia. When flowers are not initiated in the leaf axils, vegetative buds develop therein and in the terminal of the shoot. The male inflorescence is a cyme with 3 flowers and the female inflorescence a solitary flower. Both staminate and pistillate flowers normally have 4 sepal points, 4 petals, 4 anthers and 4 carpels though 5 and 6 of each are frequently observed in individual flowers. Pistillate flowers bear no pollen and staminate flowers have only a rudimentary pistil. The trimerous primordium, though variously shaped, is the origin of leaves, cataphyls, resting vegetative buds, bracts, the calyx, and the inflorescence. Differentiation into leaves or cataphyls and inflorescences or resting vegetative buds appeared to be controlled by the physiological condition of the plant at the time of differentiation.

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Resistance to mites and small insects in geranium results from the production of a viscous exudate on tall glandular trichomes present on the plant surface. This exudate exhibits sticky-trap properties immobilizing pests and reducing feeding and fecundity. The exudate is composed of long-chain 6-alkyl salicylic acids known as anacardic acids. The exudate of resistant plants contains 86% unsaturated anacardic acids. Susceptible genotypes possess fewer tall glandular trichomes and a trichome exudate which is dry and ineffective in trapping pests. The exudate from susceptible plants contains 70% saturated anacardic acids, thus explaining the physical state of the exudate. A single dominant locus controls the production of predominantly unsaturated versus saturated anacardic acids and thus resistance versus susceptibility. Other loci condition the ratio of C22:C24 unsaturated anacardic acids and the density of tall glandular trichomes. Current research involves the elucidation of the enzymatic pathway(s) involved in anacardic acid biosynthesis, identification of the regulatory enzymes and isolation of the mRNA transcripts associated with pertinent genes.

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Abstract

The enzyme-linked immunosorbent assay (ELISA) was used for the detection of tobacco ringspot virus (TRSV) in crude leaf extracts of geranium (Pelargonium × hortorum Bailey). An ELISA test protocol using a coating antibody concentration of 10 μg/ml, a 1000-fold dilution of antibody-enzyme conjugate, a substrate reaction time of 30-45 minutes, and a leaf test sample prepared in 20 volumes of phosphate buffer provided the best compromise between test reliability, conservation of reagents, and convenience. Using this protocol, significantly positive absorbante values (A405nm) were obtained with extracts from geraniums latently-infected with TRSV whereas color development form noninfected geraniums was negligible. Potentially, the ELISA represents a rapid, reliable, economical, and convenient method for virus-indexing geraniums commercially.

Open Access