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  • Author or Editor: Pablo Jourdan x
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Budgetary, logistical and time constraints frequently limit the extent of hands-on activities included in introductory courses in horticulture. Model organisms can facilitate the demonstration of broad-based principles and enhance learning. The Wisconsin Fast Plants®, rapid cycling forms of Brassica rapa, represent such a model organism with diverse and useful applications in horticultural instruction. These organisms offer not only a practical advantage for teaching, but also facilitate learning at higher levels of thinking because they permit integration of concepts at the molecular, organismal, and population levels. A large collection of educational activities is currently available with these plants that can be used to enhance understanding of basic botanical principles; many aspects of plant physiology; broad principles of crop production; genetics and plant breeding; and molecular manipulations. The educational strategy afforded by these plants will be described.

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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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Before attempting transformation of Pelargonium spp., it is necessary to develop procedures for shoot regeneration under selective conditions (kanamycin resistance). Leaf disks of various cultivars of regal, zonal, ivy-leaved, and scented pelargoniums were compared for shoot regenerability and phenolic production. Disks were cultured on MS medium supplemented with 10.7 μM NAA and 8.9 μM BA. After three weeks in darkness, each disk was transferred to MS with 0.89 μM BA and evaluated for proportion of disks with callus, extent of disk development, and the rate and intensity of phenolic halo production. Phenolic production was not correlated with shoot regeneration ability. Regal pelargoniums had low phenolic production, while ivy-leaved pelargoniums had both the highest phenolic production and callus formation. Shoot regeneration from leaf disks was inhibited on media containing 100 μg/ml kanamycin.

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The Wisconsin Fast Plants® (rapid cycling forms of Brassica rapa) have become a major educational tool in basic botany, plant physiology and plant genetics courses because of their versatility, ease of manipulation, and short life cycle (40-day generation). Various educational activities already developed by the Fast Plants Network can be incorporated effectively into established horticulture courses. We have been utilizing these plants in some of our introductory courses and have developed additional protocols and materials. Some of the new educational activities utilize the rapid cycling form of B. oleracea, Examples of these materials will be presented, including: new genetic stocks and use of isoenzyme markers; use of growth regulators (e.g., uniconazole) to modify plant growth and development; post-harvest physiology (e.g., growth, chlorophyll and starch content); hydroponics and plant nutrition; cell and tissue culture (micropropagation, anther culture, protoplast culture, transformation); and biochemical studies (e.g., enzyme isolation and characterization, extraction and characterization of DNA, etc).

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Poor seed set in P. xdomesticum hinders development of new and improved cultivars. Crossing data has indicated differences among selections in male fertility. A study was undertaken to examine the amount of male fertility in the species as evidenced by pollen staining and pollen germination and development. Eight P. xdomesticum selections were crossed as males onto two selections used as females. 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 produced in the style. Pollen from the 8 selections was tested for viability by staining with fluorescein diacetate (FDA) and examined using fluorescence microscopy. The males varied in pollen viability from 69% pollen staining producing 16 pollen tubes to 18% saining producing 3 tubes. The most fertile males produce enough pollen tubes to effect fertilization of all of the ovules in a P. xdomesticum ovary.

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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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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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Pulsatilla cernua var. koreana seeds were harvested at six different dates between 16 days after flowering (DAF) (8 Apr.) and 43 DAF (5 May) in 2018 and categorized into six groups based on X-ray images. Germination tests were performed without and with 2 weeks of moist 5 °C treatment [cold stratification (CS)]. Seeds harvested at 38 DAF (30 Apr.) with well-developed vegetative organs (embryo and endosperm) in seeds categorized as A and B (seed A and seed B, respectively) based on the X-ray images were considered fully developed, and 80% of seeds were considered mature. However, the germination rates were less than 26% or 28% when full seeds harvested at 43 DAF received no or 14 days of CS treatment, respectively. Our study suggests that the low germination rate of fully developed seeds as judged by X-ray images showing well-developed embryo and endosperm could result from the presence of dormancy that was not broken effectively by 14 days of CS coupled with the loss of viability caused by 8 months of dry storage at 5 °C.

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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.

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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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