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Mary Stuart and Pablo Jourdan

The regal pelargonium (P. x domesticum) is generally characterized by low fertility and poor seed set. In studys designed to assess factors that contribute to low fecundity in this crop we have examined genotype interactions among various cultivars and have identified lines that differ in degree of male and female fertility.

The objective of this study was to examine genotypic variation, other than self-incompatibility, of P. x domesticum pistils in supporting the development of the male gametophyte. Variation in pollen germination and growth was assessed after crossing either a male of high fertility or a mate of poor fertility to nine different selections of varying female fertility. Styles were harvested 2 hours after pollination and examined using fluorescence microscopy to determine the number of germinated pollen grains on the stigma and the number of pollen tubes growing down the style.

Female selections displayed large differences in their ability to support pollen tubes. Styles from different females pollinated with the same male varied in average number of pollen tubes from 30 to 2.

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Peter J. Zale and Pablo Jourdan

Phlox is an important genus of herbaceous ornamental plants previously targeted for germplasm development, characterization, and enhancement by the U.S. Department of Agriculture, National Plant Germplasm System. Among Phlox in cultivation, Phlox paniculata is the most widely grown and intensively bred species, but little is known about variation in genome size and ploidy of this species or of related taxa that may be used for germplasm enhancement. The objective of this study was to assess cytotype variation in a diverse collection of cultivars and wild germplasm of P. paniculata (subsection Paniculatae) and of related taxa in subsections Paniculatae and Phlox. The collection included 138 accessions from seven species and two interspecific hybrids. Flow cytometry was used to estimate holoploid (2C) genome sizes and to infer ploidy levels. Chromosome counts were made to calibrate ploidy with genome size for a subset of taxa. Most cultivars were diploid (2n = 2x = 14) and had mean genome sizes that did not vary between subsections Paniculatae (14.33 pg) and Phlox (14.23 pg) although size variation was greater among cultivars within subsection Phlox. Triploid cultivars of P. paniculata, with a mean genome size of 21.36 pg and mitotic chromosome counts of 2n = 3x = 21, were identified. Such triploids suggests previous interploid hybridization within this taxon. Five tetraploid (2n = 4x = 28) cultivars were found in subsection Phlox; all were selections of P. glaberrima ssp. triflora, and had a mean genome size of 25.44 pg; chromosome counts in one of these confirmed they were tetraploid. The putative hybrid Phlox Suffruticosa Group ‘Miss Lingard’ showed an intermediate genome size of 21.21 pg supporting a triploid, hybrid origin of this taxon. Mean 2C genome sizes among wild-collected accessions were similar to values reported for cultivars (Paniculatae = 14.59 pg, Phlox = 14.23 pg), but taxa in subsection Phlox exhibited greater variation that included two tetraploids identified among wild-collected accessions; one, of P. pulchra, had a mean genome size of 26.17 pg, representing the first report of polyploidy in the taxon. This is the first report on genome size for the majority of species in the study. Although genome size could not be used to differentiate taxa in subsections Paniculatae and Phlox, the data provide further insights into cytotype variation of Phlox germplasm useful for plant breeders and systematists.

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Richard H. Ozminkowski Jr. and Pablo Jourdan

Brassica napus (genome aacc), a natural allotetraploid derived from hybridization between B. oleracea L. (genome cc) and B. rapa L. (genome aa), was synthesized by sexual and somatic interspecific hybridizations from the same parent plants to compare the two methods of combining genomes and assess the genetic consequences of bypassing the gametophytic phase before hybrid formation. Highly heterozygous species parents were first produced by intraspecific hybridization between two subspecies each of B. oleracea and B. rapa. Leaf tissue from young plants of both parental species served as a source of protoplasts for fusion; the same plants were later used for crosses. Seventy-two somatic hybrids were produced using a polyethylene glycol-mediated fusion protocol and 27 sexual hybrids were obtained by embryo rescue. Somatic hybrids were produced between one B. oleracea and two sibling B. rapa plants. Sexual hybrids were successfully produced with only one of the two B. rapa siblings. Hybrids were identified by morphology, isozyme patterns, and total DNA content. Although fertile allotetraploid somatic hybrids were obtained within 7 months after seeding parent lines, >1 year was required to produce fertile sexual hybrids.

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Richard H. Ozminkowski Jr. and Pablo Jourdan

Brassica napus (genome aacc), a natural allotetraploid derived from hybridization between B. oleracea L. (genome cc) and B. rapa L. (genome aa), was resynthesized by somatic and sexual hybridization. Seventy-two interspecific somatic (R0) hybrids and 27 sexual (F1) hybrids were produced from the same parent plants. R0 and F1 hybrids displayed morphology that was intermediate to the species parents, but B. rapa characteristics tended to predominate. R0 hybrids with nuclear DNA content equivalent to natural B. napus were uniform for nuclear-encoded traits, whereas allotetraploid F1 hybrids were variable for traits such as morphology, flower color, and seed production. Chloroplast restriction fragment length polymorphisms (RFLPs) showed unequal segregation in the R0 population favoring the chloroplasts of B. rapa; two of the 58 R0 hybrids tested had only the B. oleracea marker and 10 contained markers of both parents. Mitochondrial RFLPs showed a similar bias among the 56 R0 hybrids tested; only four plants showed B. oleracea markers exclusively, and the remaining plants were evenly distributed between having only B. rapa markers or having combinations from both species. In contrast, sexual hybrids displayed only maternal organelle markers.

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Ann M. Chanon, Pablo S. Jourdan and Joseph C. Scheerens

As a prelude to interspecific hybridization, we compared the floral biology of bottlebrush buckeye (Aesculus parviflora) and red buckeye (A. pavia) by examining inflorescence morphology, pattern of floral anthesis, sex expression, and the effects of panicle decapitation on complete flower development. Inflorescences of both species (n = 1606) were randomly selected and analyzed for length, total number of flowers and complete flower number and location. The pattern of anthesis was observed in four genotypes using 10–30 inflorescences per plant. For each flower, its date of anthesis, position on both the rachis and cincinnus, and sex were recorded. For studies of panicle decapitation, sets of panicles were selected and one member was severed in half early in development in an attempt to increase the number of complete flowers. More than one-fourth of all panicles observed were completely staminate. For both species, the ratio of complete flowers to male flowers (C:M) within mixed panicles was about 5%. Complete flowers were observed in the basal portion of A. pavia inflorescences and in the apical portion of A. parviflora inflorescences. Anthesis progressed from base to tip over a period of 6–11 days. Complete flowers are present in A. pavia from the beginning of anthesis but do not appear in A. parviflora until the fifth day of anthesis. Staminate flowers are present throughout anthesis in both species. Severing panicles in half increased the potential for differentiating complete flowers. In conclusion, the frequency of complete flowers in both species was quite low, but could be increased by panicle decapitation to increase opportunities for controlled hybridization.

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Ann M. Chanon, Pablo S. Jourdan and Joseph C. Scheerens

The genus Aesculus (buckeyes and/or horsechestnuts) is composed of 13 species and a number of interspecific hybrids. Pollen from 11 genotypes from five Aesculus species and the hybrid Aesculus ×carnea were used to develop an in-vitro germination test to evaluate pollen viability under various storage treatments. This test was optimized using samples of both fresh pollen and pollen that had been stored up to 1 year. The most effective medium contained 20% sucrose, 100 mg·L-1 H2BO3, 150 mg·L-1 Ca(NO3)2, and 1% agar. The highest germination percentage was observed at 15 °C across all storage treatments. Fresh pollen germinated in excess of 80% over a wide range of germination temperatures. Based on this, all specimens studied would be good pollen parents. The differences in pollen germination between storage at -20 and -80 °C were nonsignificant, but the duration of the storage period was highly significant. At 3 months, viability remained above 60% for four of the six species/hybrid tested. However, at 12 months, all pollen tested dropped below the threshold for good fruit set based on in-vitro pollen germination. Based on these observations, short-term pollen storage may permit crosses between parents with temporally separate flowering phenologies. However, conventional storage procedures are inadequate to maintain pollen collected from a male parent for crosses in subsequent growing seasons.

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Peter J. Zale, Daniel K. Struve, Pablo Jourdan and David M. Francis

Breeding and development of ornamental woody plants for specific ideotypes will provide diverse choices to meet specific needs for natural and constructed landscapes. An F1 half-sib family analysis of Magnolia virginiana generated from controlled pollinations was implemented to identify potential juvenile selection strategies for two mature ideotypes: a compact and rounded shrub form (to 2.5 m tall and wide) and a single-stemmed, small tree form (to 4 m tall), both with abundant flowering. The 2-year test was conducted in a container nursery. Fourteen traits were measured in 2007 and 2008, including height at three intervals (July, August, and September), mean branch length and branch count, early and late flower production, collar sprout formation, stem diameter, and branch angle. There were significant differences between F1 half-sib families (P ≤ 0.0001) for all traits. Phenotypic and genetic correlations and narrow sense heritability were estimated for these traits. Phenotypic and genetic correlations showed favorable associations among branch count, caliper, and early flower production. These traits were used to form a selection index for a shrub ideotype. Also, there were positive phenotypic and genetic correlations between height and late flower production, which were both negatively correlated with collar sprout formation. These traits were used to form a selection index for the single-stemmed, small tree ideotype. Narrow sense heritabilities were high for most traits in 2007 but were lower in 2008. Results suggest that selection of phenotypes ranking highest for the traits of interest may yield the desired ideotypes. However, introduction of additional genetic variation through new germplasm accessions may be necessary to maintain breeding progress.

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Gladys A. Andiru, Claudio C. Pasian, Jonathan M. Frantz and Pablo Jourdan

Controlled-release fertilizers (CRFs) have not been extensively used in floricultural production, perhaps due to lack of grower experience and research-based information with their use in herbaceous plant production. Any information about the correct use of CRF should increase growers’ confidence in using this type of fertilizer. The objective of this research was to compare the growth and quality of bedding impatiens (Impatiens wallerana XTREME™ ‘Scarlet’) when grown with typical water-soluble fertilizer (WSF) and with different combinations of longevity and rates of a single formulation of CRF. The CRF 16N–3.9P–10K consisted of different longevities (3–4, 5–6, 8–9, or 12–14 months) and application rates (1.4, 3.4, 6.8, 10.2, or 13.6 kg·m−3). Plants were grown in the greenhouse, and consumer evaluations were performed at market maturity. Plant canopy cover, flower cover (FC), and shoot dry weight (DW) were also determined. Commercially acceptable plant quality was achieved with CRF application rates between 3.4 and 6.8 kg·m−3. At low CRF application rates, the faster release rate (shorter longevities) CRFs produced larger plants [DW and leaf canopy cover (LCC)] with greater flowering potential (FC) than slower release rate CRFs. At higher application rates, slower release rates (longer longevities) outperformed the faster release CRFs for the same parameters. CRF-grown plants were smaller than WSF plants when CRFs were applied at the lowest rates. No differences in any of the three variables measured were found when plants were grown at a rate of 6.8 kg·m−3 CRF of any longevity or with WSF. Growers should adjust CRF application rates according to CRF longevity.

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Clíssia Barboza da Silva, Julio Marcos-Filho, Pablo Jourdan and Mark A. Bennett

Drum priming systems are among the most common methods of seed priming for commercial treatment. The supply of water to the seeds is controlled by physical means, and seeds are able to reach a desired moisture content without the use of osmotic solutions for hydration control. The brassinosteroid (BR), 24-epibrassinolide (24-EpiBL), has been shown previously to have a significant effect on seed performance. Therefore, the aim of this study was to verify the feasibility of drum priming associated with added 24-EpiBL on enhancement of bell pepper seed performance. Two bell pepper cultivars (AF-6 and AF-7) were tested, and each cultivar represented, respectively, by three and four seed lots with different initial physiological potentials. Seed performance was determined by evaluating standard germination, initial seedling growth, and changes on the antioxidant activity of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX). Seed Vigor Imaging System (SVIS®) was used to assess the initial seedling growth. The nondenaturing polyacrylamide gel electrophoresis (PAGE) technique was used to evaluate possible changes in the enzymatic antioxidant system. Several advantages were verified in the drum priming technique with added 24-EpiBL compared with the traditional procedure (water alone). Germination time was reduced followed by a seedling growth increase. Concomitantly, seed enzymatic activity was improved. However, results showed different response for each enzyme. Drum priming with 24-EpiBL demonstrates viability for commercial treatment and enhancement of bell pepper seeds.

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Ji Hee Kim, Jeung Keun Suh, Seong-Tak Yoon, Pablo Jourdan and Mark S. Roh

Corylopsis seed germination tests were conducted to assess the influence of harvest date (seed maturity) and cold stratification (CS) at 5 °C. Corylopsis gotoana seeds harvested on 12 July, 2 and 22 Aug., 6 and 20 Sept., and 1 and 10 Oct. 2011 were immersed in water for 20 min to separate fully developed seeds (full seeds) from empty seeds by floatation, and by X-ray scanning to identify full from empty seeds (Expt. 1). Immersing seeds in water did not effectively separate full seeds from empty seeds as evaluated by seed germination tests. Seeds harvested on or around 6 Sept. that sank showed translucent X-ray images with fully developed internal structures composed of embryo, cotyledons, and endosperm, and were considered mature. Without CS, >12% seeds harvested on 20 Sept. germinated, regardless of whether seeds were full or empty. Seeds of C. coreana harvested on 5 and 15 Sept., and 5 and 18 Oct. were stored dry at 20 °C until 27 Dec. and germinated after 0, 3, 6, 9, and 12 weeks of CS (Expt. 2). Longer than 6 weeks of CS was required to accelerate and increase the germination of seeds harvested on or after 5 Sept. Germination percentage of full seeds harvested on Oct. 18 was increased to >72% as the duration of CS treatment increased to 12 weeks. In conclusion, fully developed seeds harvested on or after 6 Sept. were considered mature and 6 weeks of CS accelerated germination and increased the germination percentage. Further, dormancy of Corylopsis seeds appears to be shallow since germination occurred without any CS.