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Wenhao Dai and Victoria Jacques

Periwinkle, a perennial commonly used as a summer bedding plant, is known as the source of vinca alkaloids used to treat lymphocytic leukemia and Hodgkin's disease. It is also one of the natural hosts of many phytoplasma diseases, such as X-disease of major Prunus species, aster yellows, and ash yellows diseases. Therefore, periwinkle is an ideal plant species for phytoplasma disease research, such as disease transmission, species resistance, and resistant gene screening. Periwinkle tissue culture was established by incubating sterile seeds in hormone-free Murashige and Skoog (MS) medium. Plants were successfully regenerated from in vitro leaf tissues of periwinkle. Adventitious shoots were induced when leaf tissues were cultured on Murashige and Skoog (MS) medium or woody plant medium (WPM) supplemented with benzyladenine (BA) and naphthaleneacetic acid (NAA). Nearly 75% of leaf explants produced shoots in both media with 10–20 μm BA and 1 μm NAA. A mean of 4.3 shoots was produced from each explant cultured on WPM, whereas only 2 shoots were produced on MS medium under 16-h photoperiod. Leaf explants under dark treatment for 2 weeks produced big callus only, indicating that light is necessary for shoot formation. Most adventitious shoots were induced from the joint of leaf blade and petiole. In vitro shoots (>1.5 cm) were easily rooted in half-strength MS medium. Addition of NAA dramatically increased root number, with more than 20 roots being induced in 5 μm NAA medium. Rooted plants were transferred to potting medium and grown in a greenhouse.

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Benyamin Lakitan, David W. Wolfe, and Richard W. Zobel

Greenhouse experiments were conducted in 1987 and 1988 to evaluate the effect of timing of a 4-day flooding stress on growth and yield of snap bean (Phaseolus vulgaris L. cv. Bush Blue Lake 274, BBL). Plant survival was reduced when flooding was imposed at postflowering growth stages, but most plants survived when flooded before flowering or when reproductive development was prevented by deflowering. Early yields of surviving plants were very low in all flooded treatments, regardless of timing, in both years. Total yield response to timing of flooding was linear in 1987, with lowest yields when flooding was imposed at later growth stages. The trend was not linear in 1988, but in both years the latest flooding treatment (36 days after planting) had few surviving plants and no measurable pod yield. Additional greenhouse experiments revealed that leaf conductance of BBL and another bean cultivar, Luna (LN), declined within the first day of flooding. This decline was concomitant with one in leaf water potential and photosynthesis (Pn) in BBL, but decline of these responses occurred 1 to 2 days later for LN. After 4 days of flooding, Pn fell to near 0 for BBL, and to 15% of the prestress value for LN. Pn of both cultivars had recovered to 18.5 μmol·m-2·s-1 10 days after termination of flooding. LN had a larger adventitious root biomass, higher percentage of adventitious roots, and a consistently lower leaf: root ratio than BBL during recovery.

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Robert L. Geneve, Wesley P. Hackett, and Bert T. Swanson

Exogenous ethylene could not substitute for NAA to induce adventitious root initiation in juvenile petiole explants of English ivy (Hedera helix L.), indicating that the action of auxin-stimulated root initiation was not directly mediated through ethylene production. Mature petioles did not initiate roots under any auxin or ethylene treatment combination. Ethephon or ACC supplied at 50 or 100 μm was inhibitory to NAA-induced root initiation in juvenile petioles. The pattern of ethylene production stimulated by NAA application was significantly different in juvenile and mature petioles. Ethylene evolution by juvenile petioles declined to near control levels during from 6 to 12 days after NAA application. Reduction in ethylene production was due to reduced availability of ACC in juvenile petioles. Mature petioles continued to produce ethylene at elevated levels throughout the course of the experiment. Ethylene does not appear to play a significant role in the differential root initiation response of juvenile and mature petioles treated with NAA. However, ethylene appeared to have an inhibitory effect during root elongation stages of adventitious root development in juvenile petioles. Chemical names used: 1-aminocyclopropane-1-carboxylic acid (ACC); 1-napthaleneacetic acid (NAA); 2-chloroethylphosphonic acid (ethephon).

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Daniel I. Leskovar and Peter J. Stoffell

Initiation, development, and subsequent growth of seedling root and shoot components can have a direct influence on the quality, adaptation, and survival of seedlings, particularly under stress conditions. Taproot, basal, lateral, and adventitious root components (common indicot plants) each have their own development sequence, growth rate, and may have separate functions for subsequent seedling growth and development. Stresses originating in root components may be expressed in shoots affecting dry matter partitioning between roots and shoots. Partitioning and development of root morphological components and root/shoot growth adaptation to stress environments will be presented for various vegetable species. Implications of root developmental differences in relation to field planting methods will be discussed. Understanding seedling morphology, physiology and assimilate partitioning during early ontogeny would assist directing strategies to improve field establishment and ultimately crop production.

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Sven E. Svenson and Diane L. Johnston

Stem tip cuttings of Evolvulus glomeratus Nees & Mart., E. tenuis Nees & Mart., Lantana camara L. `Dallas Red,' and L. montevidensis Briq. `Alba' were rooted for 6 weeks in 57-mm-diameter (150 ml) square pots. Before rooting, interior surfaces of half of the pots were treated with 100 g Cu(OH)2/liter, while remaining pots were left untreated. Elongation of adventitious roots stopped when root tips came in contact with a Cu(OH)2-treated surface. Cupric hydroxide treatment reduced total root length and the length of the longest root for all four species, but did not influence root, shoot, or total plant weight. One month after transplanting to 150-mm-diameter (1.2 liter) hanging baskets, plants moved from Cu(OH)2-treated pots had more flowers than those transplanted from nontreated pots. Applying Cu(OH)2 to interior surfaces of pots used for propagation prevented root deformation, reduced root length, and increased flowering following transplanting.

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Sven E. Svenson and Fred T. Davies Jr.

Variation in tissue elemental concentration in apical stem cuttings of `Lilo' and `V-10 Amy' poinsettia (Euphorbia pulcherrima Willd. ex. Klotzch) were studied during the initiation and development of adventitious roots. Changes in selected macro- and micro-element concentrations coincided with root initiation (i.e., Fe, Cu, and Mo accumulated in the basal portions of stem cuttings during early root initiation before root primordia elongation); P, K, Ca, and Mg concentrations declined. During root primordia elongation and root emergence, Fe, Cu, and Mo and Mg, Mn, B, and Zn concentrations continued to increase at the cutting bases, but P and K concentrations remained low compared to when cuttings were initially inserted in the propagation medium. When all cutting of both cultivars had rooted, foliar N, Fe, and Mo concentrations declined, but Cu increased compared to when cuttings were initially propagated.

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Torin O. Pope and Caula A. Beyl

Agrobacterium rhizogenes is a valuable new tool for inducing adventitious roots in difficult-to-root ornamentals To evaluate species and strain interactions, three ornamental species were chosen: Hydrangea quercifolia, Pyrus calleryana, and Photinia × fraserii. Terminal shoots (2.5 cm long) were collected at bud swelling and then immersed in bleach (20% v/v) for 10 min with stirring. They were rinsed three times in sterile distilled water and cultured individually in test tubes containing 15 ml of Murashige and Skoog medium. After 3 weeks, the uncontaminated shoots were divided into five groups: four strains of A. rhizogenes and a control. There was a significant effect of strain and species in the production of callus and organs from the shoot tips. The presence of strain by host interaction was observed In the morphogenic response of explants.

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Timothy K. Broschat

Mature pygmy date palms (Phoenix roebelenii O'Brien) having a minimum of 90 cm of clear trunk were transplanted into a field nursery at their original depth or with 15, 30, 60, or 90 cm of soil above the original rootball. Palms planted at the original level or with the visible portion of the root initiation zone buried had the largest canopies, highest survival rates, and lowest incidence of Mn deficiency 15 months after transplanting. Palms planted 90 cm deep had only a 40% survival rate, with small, Mn-deficient canopies on surviving palms. Palms whose original rootballs were planted 90 cm deep had very poor or no root growth at any level, but had elevated Fe levels in the foliage. None of the deeply planted palms produced any new adventitious roots higher than 15 cm above the visible portion of the root initiation zone.

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Chiwon W. Lee, Joel T. Nichols, Lijuan Wang, and Shanqiang Ke

Excised leaf sections of lance coreopsis cultured on Murashige Skoog (MS) medium produced adventitious shoots in response to BA. When the combinations of 0, 0.5, 1, or 2 μm NAA with 0, 5, 10, 20, or 40 μm BA were tested, shoots were induced by any of the four BA concentrations used in the medium, regardless of the presence of NAA. The average number of shoots formed per leaf section ranged from 1.4 to 4.3 seven weeks after culture initiation. Roots were induced at the base of individual shoots on the same regeneration medium when cultures were kept longer than 7 weeks. The rooted plants were transferred successfully into soil. The regenerated plants had the same growth and flowering characteristics as the seed-grown plants. Chemical names used: benzyladenine (BA); naphthaleneacetic acid (NAA).

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Steven T. McNamara and Cary A. Mitchell

Tomato accessions PI 128644 (Lycopersicon peruvianum var. dentatum Mill.) and PI 406966 (Lycopersicon esculentum Mill.) were identified in preliminary screening trials as being relatively nonresistant and resistant to 120 hr of flooding, respectively. Many adventitious roots (AR) developed on the lower stems of flooded PI 406966 seedlings, while few formed on flooded PI 128644 plants. Root formation by flooded PI 406966 seedlings depended on de novo initiation rather than emergence of preformed initials. Hypocotyl porosity of PI 406966 plants increased from between 3% and 6% to 8% by 36 and 72 hr of flooding, respectively. Porosity of PI 128644 hypocotyls was unchanged by 72 hr of inundation. Flooding did not affect the secondary root porosity of either accession. The limited capacity of PI 128644 seedlings to develop AR and aerenchyma was not related to an inability to synthesize 1-aminocyclopropane-l.carboxylic acid or ethylene in response to hypoxia. Chemical name used: 1-aminocyclopropane-1-carboxylic acid (ACC).