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Abstract
The total number and length of new shoots of Leucothoe catesbaei Gray were significantly greater, and the plants were of better quality with NO3 nutrition than with NH4 or urea nutrition. Especially with the NH4-N sources, growth was as good as or significantly greater at pH 6 to 7 than at 4 to 5. The total number and length of new shoots of Rhododendron catawbiense Michx. cv. Roseum Elegans were not significantly affected by the N source or pH, although plant appearance was significantly better with NO3 nutrition than with NH4 or urea nutrition. The nitrification inhibitor, a substituted pyridine, had no significant effect on the growth and development of either leucothoe or rhododendron.
The correct identification of horticultural taxa becomes more and more important for intellectual property protection and economic reasons. Traditionally, morphological characteristics have been used to differentiate among the horticultural taxa. However, the morphological characteristics may vary with plant age, cultural conditions, and climate. Modern technologies, such as DNA markers, are now employed in the identification of horticultural taxa. Currently, technologies of DNA sequencing (gene sequences) and DNA fingerprinting (RAPD, RFLP, SSR, and AFLP) are available for distinguishing among horticultural taxa. The literature and our personal experience indicate that the application of each technique depends on the taxon and ultimate goal for the research. DNA sequencing of a variety of nuclear or chloroplast encoded genes or intergenic spacers (rbcL, ndhF, matK, ITS) can be applied to distinguish different species. All DNA fingerprinting technologies can be used to classify infraspecies taxa. AFLP (the most modern technique) is the better and more-reliable to identify taxa subordinate to the species, while RAPDs can be employed in clonal or individual identification. Techniques of RFLP and SSR lie between AFLP and RAPD in their effectiveness to delineate taxa. Mechanics, laboratory procedures, and inherent difficulties of each technique will be briefly discussed. Application of the above technologies to the classification of Cephalo taxus will be discussed in concert with the morphological and horticultural characteristics. Future classification and identification of horticultural taxa should combine DNA technology and standard morphological markers.
Abstract
Mung bean (Phaseolus aureus Roxb.) cuttings and cucumber (Cucumis sativus L. cv. Marketer) seedlings were cultured in water extracts of bark from silver maple (Acer saccharinum L.) hackberry (Celtis occidentalis L.), sycamore (Platanus occidentalis L.) and cottonwood (Populus deltoides Marsh.). Extracts of fresh silver maple bark inhibited root elongation of cucumbers and the adventitious rooting of mung bean. Composting the silver maple bark for 30 days prior to preparing the water extracts reduced inhibition. Pretreatment of fresh silver maple bark extracts with insoluble polyvinylpyrrolidone (PVP) reduced inhibition and indicated that the inhibitory compound was phenolic in nature. Chromatography and spectral analysis of common phenolic compounds and silver maple bark extracts revealed the toxic substance was similar to tannic acid.
Positive cultivar identification is often difficult or impossible based solely on morphological traits. A technique ensuring reliable, repeatable, and unique cultivar identification is needed. The use of molecular markers offers such a technique, allowing assessment of fine levels of variation directly at the DNA level. In this study, RAPD (Random Amplified Polymorphic DNA) markers were investigated for their utility to identify red maple cultivars. Three out of nineteen primers tested resulted in unique banding patterns for all the maples tested, including 9 red maple clones, 5 silver maple seedlings, and 4 purported interspecific cultivars. The red maple cultivars `Red Sunset' and `October Glory', which are almost indistinguishable morphologically as young trees, were clearly distinguished using RAPD markers. Thus, RAPD markers provide a consistently reliable technique for red maple cultivar identification.
Lysimachia congestiflora Wils. (Primulaceae) is a new crop for American nurseries and may be used as an annual in the north and a half-hardy perennial in the south. The purpose of this study was to investigate the influence of photoperiod, temperature, and irradiance on its flowering and growth. Three experiments were conducted with photoperiod of 8, 12, 16 hrs day-1, temperature of 10, 18, 26C, and irradiance of 100, 200, 300 μmol m-2s-1, respectively. Plant.9 given long day photoperiod (16 hours) flowered 21 and 34 days earlier, respectively, than plants at 12 sad 8 hour photoperiods. Plants under long day treatment produced more flowers than those at 8 and 12 hours. Plant dry weight did not differ between treatments, but plants grown in the long day treatment produced fewer but larger leaves. Total plant growth increased as temperature increased, but lower temperature (10C) decreased flower initiation and prevented flower development, while high temperature (26C) reduced the longevity of the open flowers. Flowering was accelerated and dry weight increased as plants were subjected to high irradiance levels. The results suggest that Lysimachia congestiflora is a quantitative long day plant. It should be grown under a photoperiod of at least 12 hours at a temperature of approximately 20C. Low light areas should be avoided and supplemental lighting to provide the long days may improve the plant quality.
Two experiments were conducted to determine the effect of drought stress on the susceptibility of Buddleia davidii Franch. `Pink Delight' to the two-spotted spider mite (Tetranychus urticae Koch). In the first experiment, drought stress was imposed by withholding water until predawn xylem pressure potential fell below -1 MPa. Shoot growth was 75% less in drought-stressed than in nonstressed plants. Mite population densities were not affected, but noninfested leaf area was 14% higher, and degree of mite damage was lower, in nonstressed plants. Evidently, the greater amount of new growth in nonstressed plants leads to lower spider mite densities by diluting populations. In a second experiment, nonstressed B. davidii `Pink Delight' plants were watered every 1 to 2 days and drought-stressed plants were watered every 3 days. Spider mite populations were monitored by sampling newly expanded and mature foliage. Mite populations on mature foliage were not affected by stress, but stressed plants grew less and had larger spider mite populations on their newly expanded foliage than did nonstressed plants.
The genetic diversity among H. macrophylla (Thunberg) Seringe taxa is limited as a result of the restricted native distribution and multiple breeding programs that used the same taxa and targeted similar breeding goals. This study assessed the compatibility of interspecific crosses between Hydrangea macrophylla and H. angustipetala Hayata as a source of genetic diversity. Two lacecap cultivars of H. macrophylla, ‘Lady in Red’ and Midnight Duchess® (‘HYMMAD II’), were compatible with H. angustipetala. Hybridity of progeny was confirmed by simple sequence repeat markers and morphological comparisons. Some hybrids had red- or purple-pigmented stems, which are characteristic of ‘Lady in Red’ or Midnight Duchess®, respectively. All hybrids had white lacecap inflorescences. Some of the hybrid flowers were fragrant. Winter leaf retention of the hybrids ranged from deciduous to semievergreen. Male fertility of progeny was evaluated by fluorescein diacetate staining of pollen. ‘Lady in Red’, Midnight Duchess®, and H. angustipetala had 62%, 58%, and 79% stainable pollen, respectively, whereas the ‘Lady in Red’ × H. angustipetala and Midnight Duchess® × H. angustipetala hybrids had means of 48% and 47% stainable pollen, respectively. Selected progeny were used to develop F2 and BC1 populations. The interspecific hybrids produced in this study were attractive, fertile plants that are being used in further breeding to develop new cultivars.