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J. Frick and C.A. Mitchell

Due to its short time to flower (14-18 days) and rapid maturation cycle (50-55 days), dwarf rapid-cycling brassica (Brassica napus) is under consideration as a candidate oilseed crop for NASA's Controlled Ecological Life Support Systems program. Recent work has focused on defining a set of optimum environmental conditions which permit increased crop yield in terms of g·m-2d-1 of edible biomass. A wide range of environmental variables have been considered including lamp type, CO2 level, nutrient solution pH, and planting density. In addition, nitrogen nutrition regimes have been manipulated with respect to nitrogen concentration (2 to 30 mM), source (NH4 + and/or NO3 -), and time of stepwise changes in nitrogen level (day 14 to 28). The highest seed oil content (42% DW basis) has been found under limiting nitrogen levels (2 mM). However, the low nitrogen inhibits overall seed production potential. Different cultural techniques also have been compared, including solid-substrate, passive wicking hydroponics versus liquid culture systems. Trials are underway to assess crop growth and development under the “best set” scenario of environmental conditions. At present, the highest seed yield (10.6 g·m-2d-1) has been obtained using solid-substrate hydroponic systems under a combination of metal halide and high-pressure sodium lamps. Constant CO2 enrichment to 1000 μmol·mol-1 did not increase crop yield rate.

Research supported in part by NASA grant NAGW - 2329.

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B.H. McCown, E.T. Jordan, C.H. Chen, D.D. Ellis, and R.D. Vierstra

Although the size of pot mums can be controlled with retardants, the use of such chemicals may become limited. Genetically dwarfing current cultivars may be an alternative. Using a construct including a chimeric oat phytochrome structural gene, tobacco phenotypes have been produced that strongly resemble retardant-treated plants. We wished to insert this construct in mum by using particle bombardment and determine the effects on plant size and flowering dynamics. A target system was developed using `Iridon' mum leaf sections regenerated on an IAA/BA medium. Shoots developed from surface cells principally at the cut edges. Regenerates were grown-on through flowering and no visual aberrations were apparent. Levels of 50 to 100 mg/l kanamycin were inhibitory to bud development. Sections were exposed to gene transfer and shoots recovered that appear resistant to kanamycin. Some appear chimeric while others appear to be escapes stimulated by a `feeder' effect from nearby transformed cells. Further analyses will determine whether some plants are stably transformed. (Supported by a Duffett Research Grant from Yoder Brothers, Inc.)

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Kyung-Ku Shim, Yoo-Mi Ha, and Jae-Ho Ha

This cultivar originated from a grafting mutant in grafted plants of a selected 100-year-old seedling of Hibiscus syriacus L. for 5 years. In 1999, the plant is named H. syriacus `Andong'. Hibiscus syriacus `Andong' is a deciduous, erect-growing, multiple-stemmed, dwarf type that, in 7 years, has grown 120 cm high and 65 cm wide, with dense branching to the base. It has more than 200 flowers in a 7-year-old tree. The alternate, leathery, waxy, dark green leaves are 5.3 cm long, 3.8 cm wide. But it is 0.48 mm thick and 34.42 mg/cm2 of fresh weight and then is thickier and heavier than that of other cultivars. Therefore, the plant is rarely damaged by aphids and is reliably hardy to -20 °C. The flowers are white with a prominent dark red eye spot that radiates along the veins to midpetal, 5-7 cm in diameter, and blooms profusely from July to October. Total flowering time of `Andong' was 36 h in both 1998 and 1999. It sets very little fruit. AIt does not only germinate by pollen, but also by seeds. This cultivar can be readily propagated by softwood (on 24 July with 7000 ppm IBA in the mist) or hardwood cutting (1000 ppm IBA) and by grafting on seedling H. syriacus understock.

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Hamidou F. Sakhanokho, Anthony L. Witcher, Cecil T. Pounders, and James M. Spiers

’s Nursery of Nashville, NC. Developing new dwarf compact cultivars with novel foliar characteristics is a major objective of the Hedychium breeding program at the USDA-ARS Thad Cochran Southern Horticultural Laboratory (TCSHL) in Poplarville, MS. Reported

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Zhanao Deng and Brent K. Harbaugh

glasshouse in Wimauma, FL, 2007. z Recommendation UF 44-4 is a new lance-leaved cultivar with a novel combination of leaf color and shape (dwarf red with slightly undulated and rounded leaves). Plants of UF 44-4 produce a superb number of bright red leaves in

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Dean E. Knavel and Robert L. Houtz

Plants of Main Dwarf, a short-internode mutant of the normal-internode `Mainstream' muskmelon (Cucumis melo L.), have shorter internodes, fewer nodes, less total vine length, less total dry weight, smaller leaves, increased chlorophyll concentrations, increased specific leaf dry weight, and increased ribulose-1, 5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39, rubisco) activity per unit leaf area than `Mainstream' plants. Main Dwarf plants produce an equal number of fruit as `Mainstream' plants but are only half their size. Many of the plant and fruit characteristics for F1(Main Dwarf × `Mainstream') are similar to those of `Mainstream', except for greater leaf chlorophyll and rubisco activity per unit leaf area. The F1 (`Mainstream' × Main Dwarf) produced fewer and lower weight fruit than its reciprocal, F1 (Main Dwarf × `Mainstream').

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Wenhao Dai, Bingcheng Sheng, and Zhen Zhang

`Xiao Fang Shi' is a rare, dwarf cultivar of persimmon (Diospyros kaki Linn cv.) recently found north of Shanghai, China. The tree starts to bear fruit at 2 years of age, while standard trees start fruiting at 5 or 6 years of age. Dwarf and standard cultivars have about equal spring shoot growth, but the dwarf cultivar has little fall growth. To determine the mechanisms of dwarfness and early fruiting, enzyme-linked immunosorbant assay (ELISA) was used to analyze the endogenous indoleacetic acid (IAA), gibberellic acid (GA1+3) and abscicic acid (ABA) contents in leaves and shoot tips of dwarf (`Xiao Fang Shi') and standard (`Da Fang Shi' and `Zhu Sha Hong') persimmon. The measurement was done during the entire growing season. The results showed that IAA, GA1+3, and ABA contents were influenced by cultivars, ages of trees, and phenophases. The dwarf cultivar `Xiao Fang Shi' has lower IAA and GA1+3 but higher ABA contents than the two standard cultivars during the growing season. These correlations are especially evident when the fruit is ripening. The correlation coefficiency between contents of IAA and GA1+3 and tree height was 0.9704, while that between ABA content and tree height is –0.9697. The low IAA and GA, and high ABA contents may be responsible for little shoot growth of the dwarf cultivar in the fall.

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Frank Suozhan Cheng and Mikeal L. Roose

`Flying Dragon' Poncirus trifoliata L. Raf. is a dwarfing rootstock for citrus. Inheritance of dwarfing ability was studied in a population of open-pollinated seedlings of `Flying Dragon'. Molecular marker genotypes suggest that all seedlings originated from selfing. Progeny seedlings were budded with `Cutter Valencia' orange and planted in the field to evaluate the dwarfing effect of the seedling rootstock. At 5 years after planting, rankit analysis of the frequency distributions of trunk cross-sectional area and canopy volume suggested the presence of two overlapping distributions of 34 dwarf trees and 7 nondwarf. This ratio is consistent with inheritance of rootstock dwarfing as a single dominant gene for which `Flying Dragon' is heterozygous. Two morphological characteristics of `Flying Dragon', curved thorns and twisted trunk growth, were closely linked to, or pleiotropic effects of, the dwarfing gene. Bulked segregant analysis was used to identify three RAPD markers linked to the dwarfing gene. `Flying Dragon' was identical to nondwarfing cultivars of trifoliate orange at 40 homozygous and heterozygous isozyme and RFLP markers; therefore, it is likely that `Flying Dragon' originated as a mutant of a nondwarfing genotype and has not undergone sexual recombination since this event.

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Haim D. Rabinowitch, Batya Friedlander, and Ross Peters

Recently, a dwarf scape mutant was found in `Autumn Beit-Alpha' onion (Allium cepa L.). The development of dwarf scape in onion, the genetic control of this attribute, and its response to external application of ethephon and GA3 were studied. Data from segregating populations conclusively showed that a single recessive gene, designated dw1, controls scape dwarfness in onions. Its expression is slightly modified by minor genes. Relatively slow growth and early cessation of cell elongation are the characteristics associated with scape dwarfness. A similar developmental pattern characterized emerging normal flower stalks treated with ethephon. GA3 application at 50 ppm had no effect on scape elongation of dwarf plants. In each of 3 years, dwarf genotypes always produced scapes about half the length of normal ones. The marked expression stability of the dw 1 gene will facilitate its introduction into onion cultivars. Providing there is no negative pleiotropic effect, the dwarfness gene is expected to reduce lodging and, thus, improve mechanical harvest of onion seed. Chemical names used: 2-chloroethyl phosphoric acid (ethephon), gibberellic acid (GA3).

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I.L. Goldman

Few genes have been identified in red beet. A spontaneously occurring dwarf mutant was identified in the late 1970s and again in 1994 in several breeding populations. Mutant plants are characterized by extreme dwarfing of both root and shoot. Young leaves are narrow, thin and strap-like while older leaves are thicker and deeply veined. The shoot axis forms a compressed rosette. Neither the shoot axis nor the root axis of field-grown plants exceeds 3 cm in height. Genetic analysis of F2 and backcross populations revealed the dwarf phenotype is conditioned by a single recessive gene. Several experiments were conducted to determine if the dwarf phenotype was due to a lack of gibberellic acid (GA) production. Exogenous application of GA3 at concentrations ranging from 1 to 1000 ppm on dwarf plants a) following seeding and b) during reproductive growth revealed a linear increase in plant height. Control dwarf plants receiving a water-only treatment were 18% as tall as plants receiving regular application of 1000 ppm GA3. A wild-type phenotype during reproductive growth was recoverable following regular GA3 application.