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  • Author or Editor: Richard Craig x
  • Journal of the American Society for Horticultural Science x
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Floral ontogeny of two cultivars of Pelargonium ×domesticum L.H. Bailey, (regal pelargonium) `Duchess' and `Jennifer', was examined. Plants of both cultivars were grown together in a growth chamber at 15.5 °C with a photosynthetic photon flux of 10 mol·m-2·d-1. Meristems were examined at 5-day intervals over an experimental period of 170 days. The initial vegetative meristem was convex with leaf primordia initiated on either side in an alternate pattern. Early floral initiation was characterized by formation of two clefts on either side of the meristem. Between the clefts new meristems developed. Proliferation of meristems continued until numerous meristems were organized in a cluster arrangement at the apex of the shoot. New meristems lacked leaf primordia and would develop into flowers. Floral organ primordia on a floral meristem were initiated in a succession of four whorls: sepals, petals, androecia, and gynoecium.

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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.

Open Access

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.

Open Access

Interspecific hybrids of exacum (Exacum L.) display variable responses to zinc nutrition. Our research compared two genotypes with contrasting zinc efficiency phenotypes in terms of root cation exchange capacity (CEC), whole plant 65Zn uptake, and the effects of Cu+2 and Mg+2 on 65Zn uptake and partitioning to shoot tissues. Results show that the zinc efficient and inefficient genotypes had significantly different root CEC [27.2 and 16.9 cmol(+)·kg-1 root dry weight (DW), respectively] and whole plant 65Zn uptake rates (0.048 and 0.026 μmol·h-1·g-1 DW, respectively). In equimolar concentrations to Zn+2, Cu+2 reduced Zn+2 uptake by approximately 50% in both genotypes while supplemental Mg+2 enhanced Zn+2 uptake. In addition, Mg+2 facilitated a larger proportion of absorbed 65Zn to the upper shoot of the efficient genotype. We conclude zinc is absorbed through a specific Zn+2/Cu+2 transporter and that zinc efficiency in exacum is based on a combination of apoplastic and symplastic traits. In addition, a secondary Mg+2 × Zn+2 interaction may contribute to the zinc efficiency phenotype.

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Foliar evaluations for Botrytis resistance of greenhouse grown plants were performed on 45 cultivars and control genotypes including diploid and tetraploid zonal (P. ×hortorum L.H. Bailey) and ivy (P. peltatum (L.) L'Hér. in Ait.) pelargoniums. Additional evaluations were performed on eight species within section Ciconium and on progeny of a susceptible by susceptible cross-pollination involving the cultivars Ben Franklin and Marilyn. Differential levels of resistance were observed. Among many genotypes that exhibited resistance, two genotypes had consistently high levels of Botrytis resistance over several experiments. These two genotypes were the diploid P. peltatum accession 86-23-1 and the tetraploid P. ×hortorum cultivar Fox. The diploid P. ×hortorum cultivar Ben Franklin was a reliable susceptible control in all experiments. Plants grown outdoors generally had higher levels of resistance than comparable greenhouse grown plants. Orthogonal contrasts indicated no trends in resistance when comparing diploid and tetraploid pelargoniums, or when comparing among ivy, zonal, and floribunda types. Genotypes patented or introduced since 1990 have greater susceptibility than older genotypes. Cross-pollinations among susceptible parents resulted in susceptible progeny, while self-pollinations of a resistant parent resulted in resistant progeny.

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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.

Open Access

Ethylene induces significant petal abscission in regal pelargonium (Pelargonium ×domesticum L.H. Bailey). Three genotypes, `Elegance Silver' and its progeny, 00-43-1 and 00-43-2, were developed with exceptional production and postproduction characteristics. These genotypes had significantly enhanced individual floret longevity and whole plant longevity, and displayed more than twice as many florets as commercial cultivars. Dose response analysis demonstrated that `Elegance Silver' has reduced ethylene responsiveness throughout floret development, shown by lower petal abscission than other cultivars over a range of ethylene concentrations. Floret longevity was strongly correlated with ethylene responsiveness as indicated by S50 (ethylene concentration for 50% petal abscission), but not with ethylene production. These results suggest that reduced ethylene responsiveness is an important determinant of enhanced postproduction performance in the superior genotypes of regal pelargonium.

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Biochemical and morphological components of 16 Pelargonium species and the P. ×hortorum interspecific complex were examined. Inflorescences and leaves of each species were analyzed for anacardic acids and the presence of glandular trichomes. Three species of the section Ciconium, P. acetosum, P. frutetorum, and P. inquinans, produced anacardic acids in association with glandular trichomes. only P. inquinans and P. frutetorum contained ω5- anacardic acids. An evolutionary model for the origin of anacardic acids and ω5- desaturation is proposed.

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Composition of anacardic acids (phenolic acids known to be associated with small pest resistance in Pelargonium ×hortorum) was examined in 13 diploid and 25 tetraploid cultivars by high-performance liquid chromatography (HPLC). The presence of an unusual desaturation (omega (ω)-5) in the alkyl tail of anacardic acids present only in glandular trichome exudate of pest-resistant diploid inbred lines had previously been associated with a sticky-trap pest-resistance phenomenon. In this study, we examine Pelargonium cultivars for variability in anacardic acid composition to assess the distribution of ω5 desaturation among commercial cultivars, to determine possible interactions between ω5 desaturation and other plant desaturation mechanisms, and to examine the possible impact of ploidy on ω5 desaturation. An unsaturation index (UI) is derived to compare exudates differing widely in composition yet which may provide a similarly effective sticky-trap pest-resistance mechanism based on exudate viscosity. ω-5 Anacardic acids were observed in the glandular trichome exudate of all 38 commercial cultivars examined. No diploid cultivar produced ω5- and ω9- anacardic acids, although the simultaneous production of ω5 and ω9- anacardic acids was observed in three tetraploid cultivars. Total ω5- anacardic acids comprised from 42.4% (tetraploid cultivar Perlenkette-syn. Snowhite, Weiss) to 86.8% (tetraploid cultivar Amanda). Commercial P. ×domesticum cultivars had no ω5 anacardic acids. UIs ranged from 60.9 (tetraploid cultivar Dixieland) to 103.4 (diploid cultivar Pinto White). In contrast, anacardic acids collected from a pest-susceptible inbred line contained no ω5- anacardic acids and had a UI of 38.7. No significant differences among ploidy levels were observed for UIs or for most specific anacardic acid components, with the exception of 24:1 ω5- anacardic acid, in which the mean diploid value (32.1%) was significantly higher than that of the mean tetraploid value (27.6%). We conclude that ω5- anacardic acid production occurs in all Pelargonium cultivars observed and that these cultivars are predicted to exhibit resistance to small arthropod pests. Significant genetic variability in specific anacardic acid composition appears to exist among Pelargonium cultivars, suggesting that breeding for pest resistance can be readily monitored by HPLC of anacardic acids.

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Abstract

Several factors which influence the detection of tobacco ringspot virus (TRSV), by the enzyme linked immunosorbent assay (ELISA) in leaf extracts of geranium (Pelargonuim × hortorum Bailey), were examined. Crude leaf extracts could be used in ELISA to rapidly index geraniums for TRSV, providing measures were taken to minimize the effect of leaf substances which were inhibitory to the ELISA reaction. Optimal detection of TRSV (50 ng/ml) was obtained by extracting leaves in a 20-fold excess (w/v) of either 0.02M phosphate buffer, pH 7.4 containing 0.15M NaCl, 0.05% Tween 20, and 2% polyvinyl pyrrolidone or 0.1M phosphate buffer, pH 7.0 containing 4% polyethylene glycol. Clarification of the extract with polyethylene glycol and NaCl provided a 5-fold higher test sensitivity. ELISA proved useful for the detection of TRSV in both clonal and seedling geranium leaves as well as in geranium seed. The test was found to be more reliable than a bioassay for the detection of virus in the latent stage of infection.

Open Access