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  • Author or Editor: Richard Craig x
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Abstract

This is an age of transition for horticultural plant breeding. The recent developments in physiological and biochemical genetics and their application to plant breeding signify only the beginning of this new era. To define the term New Genetics is extremely difficult especially when it is applied to horticultural plant breeding. For the purpose of this paper New Genetics will mean all of. those methods, machines, ideas and information that can assist in the future breeding of better horticultural plants.

Open Access

Nine cultivars of Pelargonium × domesticum representing three germplasm sources 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 mols/day for a 16-h photoperiod in environmental growth chambers at constant 15.5 °C. Meristems were examined at 50-mol intervals (0 to 350 mols) for morphological changes associated with floral initiation. Two phenotypes were identified, cultivars with an association between floral initiation and irradiance and those with association between floral initiation and chronological time. Genotypic variation was observed among the cultivars of each phenotype.

Free access

The Plant Systematics course at Penn State University was reformatted in 1995 based on a three-dimensional model. It now includes several collaborative learning activities: a learning fair hosted by the enrolled students for elementary school students; applied laboratory exercises; and applied laboratory examinations. Each activity has a specific objective and was constructed to strengthen teaching effectiveness and to aid students in developing useful skills for future employment. A survey was administered to students enrolled in the course from 2003 through 2005 in part to assess the collaborative learning activities. Most students “strongly agreed” or “agreed” that they liked working in collaborative groups and learned from other group members. Students preferred working in groups for laboratory examinations more than for the Asteraceae Fair and learned more from their peers while completing the laboratory exercises than in laboratory examinations. Student participation in the lecture portion of the course increased as collaborative learning activities were completed. Camaraderie with peers through group work may have created an atmosphere conducive to participation and/or involvement during lectures. Organization and planning were vital to the success of these activities, as were using small groups and providing adequate incentives for completing activities. These activities engaged students to become active participants in the teaching and learning process.

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Floral initiation signals the commencement of sexual reproduction in angiosperms. In many plant species this developmental phase is controlled by photoperiod. However, it may be regulated by other factors, such as plant age or specific temperature or irradiance requirements. Floral initiation occurs in Pelargonium ×domesticum (regal Pelargoniums) in response to exposure to cool (7–12°C) temperatures for about 4–6 weeks, or to cumulative irradiance at 18–23°C. Broad genetic variability exists so that floral initiation in some cultivars is almost completely controlled by temperature, while in others it is almost completely controlled by cumulative irradiance. Among the latter group of genotypes, genetic variability exists for the amount of irradiance required. The purpose of this study was to determine the precise irradiance requirements for nine commercially important cultivars. The cultivars varied significantly in their response to irradiance with respect to floral initiation. Low irradiance requiring genotypes developed visible (5 mm) buds with as little as 250 mol of total cumulative irradiance; floral initiation in these cultivars occurred with only 50 mol of irradiance. High irradiance requiring genotypes still had vegetative meristems after 300 mol of total cumulative irradiance. Further studies were conducted on `Majestic', chosen for its high irradiance requirement. The objective of this study was to determine whether cool temperatures (7–12°C) or heat stress (23–28°C) could replace the irradiance effect. The results indicated that neither of these environmental conditions could replace the effects of moderate temperature (18–23°C) and high cumulative irradiance in this cultivar.

Free access

Research in Penn State's Exacum breeding program has revealed genotypic variation for the development of zinc deficiency, which may indicate the presence of zinc efficiency factors. Through preliminary experiments, we have identified both genetic families and individual genotypes that can be classified as either zinc-efficient or zinc-inefficient. Chi-square contingency analyses indicate significant differences (P < 0.001) in segregation patterns for zinc deficiency among hybrid families. Segregation patterns within families ranged from 100% of the progeny developing zinc deficiency to 100% of the progeny remaining healthy. Two genotypes contrasting in zinc efficiency have been identified and used in experiments designed to investigate physiological factors related to zinc efficiency. The zinc-efficient genotype has a significantly higher ability to decrease solution pH (P < 0.01), significantly higher root cation exchange capacity (P < 0.007), significantly lower root/shoot ratio (P < 0.001), significantly lower water loss/cm2 leaf (P < 0.03), and significantly higher fresh weight/dry weight ratio (P < 0.001). Research on zinc uptake rates is currently being conducted utilizing the efficient and inefficient genotypes. Based on all of our research, we conclude that 1) a strong genetic effect is involved in the zinc nutritional status of interspecific Exacum hybrids and 2) a number of physiological traits differ between zinc-efficient and zinc-inefficient genotypes.

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The morphology of interspecific Exacum hybrids was investigated in order to determine transmission patterns of several horticultural traits and to confirm interspecific hybrid status of plants. The evaluations utilized 557 accessions from interspecific hybridization of the following species: Exacum. macranthum, E. pallidum, E. pedunculatum, E. trinervium ssp. ritigalensis, and E. trinervium ssp. trinervium. Transmission patterns are proposed for stem shape (three phenotypes- clylindrical, winged-cylindrical and qudrangular; no dominance), petal shape (two phenotypes-rounded and acuminate; rounded dominant to acuminate) and flower form (two phenotypes- imbricate and separate; imbricate dominant to separate) Examination of the progenies confirm interspecific hybridization by the appearance of combinations of traits from the parental species and/or the observation of unique forms not previously observed.

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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.

Free access

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.

Free access