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- Author or Editor: C. I. Lee x
The histological and histochemical changes in developing seeds of Cypripedium debile Rchb. f., a native slipper orchid species with horticultural potential, were investigated. The effects of timing for seed collection, culture media, and cultural conditions were also examined. The optimum germination percentage occurred when mature seeds were collected and sowed on 1/4 Murashige and Skoog basal medium. Besides, the liquid culture promoted germination of mature seeds. This finding is contrary to most other Cypripedium species, which are relatively easy to germinate with immature seeds. Moreover, two notable cytological changes of C. debile were observed. First, the suspensor cell protruded beyond the micropyle opening of the inner seedcoat, making the inner seedcoat not substantial. Second, Nile red staining indicated that the deposition of cuticular material on the seedcoat was fragmentary. It is proposed that the less hydrophobic nature of the seedcoat makes mature seeds of C. debile easier to obtain water and nutrients for germination.
Chrysanthemum morifolium cv. Brilliant Anne was grown in 13 different media under frequent irrigation such that all media were nominally at container capacity. Media were selected to represent a range in airfilled porosity (0–20%) at container capacity with a depth of 12 cm. Substantial addition of organic amendment (40–90% v/v) improved aeration in a poorly aggregated loam and in two sands. Peat plus vermiculite had the best aeration of all media. Thirty day top yields were related to aeration properties of the media measured at container capacity. A value of 10–15% air-filled porosity was generally related to best growth. Oxygen diffusion rate (ODR) for the medium profile provided a better correlation with plant growth than air-filled porosity. A profile ODR of 45g O2 × 10‒8 cm-2 min-1 and above gave best growth.
The root-regenera ting potential (RRP) of one-year-old Pistacia chinensis seedlings at different growth stages was determined by recording the number of newly initiated roots during the period of 4 weeks after bare-root transplanting into a bottom misting chamber. RRP of intact pistacias was greatest when leaves were fully expanded and the terminal bud was forming (stage III) and lowest when seedlings were in a dormant condition (stages V and VI). However, seedlings disbudded before transplanting and also root cuttings showed two peaks in RRP; one at spring bud break (stage I) and the other at stage III. Removal of buds resulted in decreased RRP at stage I, but had little effect when plants were dormant. Treatments such as thiourea sprays of growing seedlings and chilling of dormant seedlings enhanced bud break and RRP. Potassium indolebutyrate applied to the root system promoted RRP of pistacia seedlings but did not eliminate the seasonal variation of RRP. Potassium indolebutyrate could replace the influence of buds only when seedlings were not in a dormant condition. Sucrose feeding via the stem substantially increased RRP at spring bud break. The results indicate that the dormant condition of buds and the availability of carbohydrates are the factors controlling the RRP of bare root transplanted pistacias.
An inverse correlation between number of roots regenerated and diameter of root segments (except fibrous roots) was found in Rosa ⨯ Noisettiana cv. Manettii. Length of regenerated roots was proportional to the diameter of root segments. The root-regenerating potential varied among scion cultivars. Manetti root segments regenerated best with rose scion cultivar ‘Cara Mia’, and least with ‘Golden Wave’.
Root regeneration from root cuttings of both difficult-to-transplant Pistacia chinensis and moderately easy-to-transplant Liquidambar styraciflua was studied in a sphagnum peat medium varying from 0-100% Ca saturation and from 0-50% air filled porosity. Maximum root regeneration of Pistacia root cuttings was obtained at 75% Ca saturation and 30% and 40% air filled porosity, whereas Liquidambar root cuttings regenerated roots best at 25% Ca saturation and at 20% to 40% air filled porosity. Indolebutyric acid applied to the root cuttings greatly increased root-regenerating potential of Pistacia root cuttings but did not affect the optimum Ca and aeration requirement(s). Similarly, indolebutyric acid treatment greatly promoted the root-regeneration potential of Liquidambar root cuttings. Satisfactory root-regenerating conditions of both Ca saturation and air filled porosity for Liquidambar root cuttings were a little broadened by indolebutyric acid (IBA) application.
Pistacia bare root seedlings also required high levels of Ca saturation and aeration for optimum root regeneration. Considerably greater numbers of roots were regenerated in peat having 75% Ca saturation and 20% air filled porosity than in peat having 0% Ca saturation and 5% air filled porosity. Root regeneration was not improved by increasing only the air filled porosity when Ca was low.
Rooting of stem cuttings of Bougainvillea cv. San Diego Red, Ceratonia siliqua L., Chrysanthemum morifolium Ramat. cvs. Golden Anne and Mandalay, Euonymus japonica L. cv. Yellow Edge, Euphorbia pulcherrima Willd. cv. Eckspoint C-1 Red, Hedera helix L., Trachelospermum jasminoides [Lindl.] Lem., Juglans hindsii (Jeps.) Jeps., Pistacia chinensis Bunge, and Salix laevigata Bebb. is greatly promoted by basal dipping in H2SO4 prior to applying indolebutryic acid. Pre-treatment with NaOH results in considerable increase of rooting of cuttings of Rhododendron (Pericat) cv. Sweetheart Supreme, Bougainvillea, Liquidambar styraciflua L., Osmanthus heterophyllus G. Don cv. Ilicifolius, and Pinus radiata D. Don.
Changes in endogenous abscisic acid (ABA) concentrations were investigated in developing seeds and the pretreated seeds of Calanthe tricarinata, a hard-to-germinate terrestrial orchid. ABA concentration was as low as 2.16 to 2.26 ng·mg−1 fresh weight at the proembryo stage [60 to 90 days after pollination (DAP)] and then continuously increased to 11.6 ng·mg−1 fresh weight at 210 DAP. Seed maturation was accompanied by a dramatic decrease in water content and a prominent accumulation of protein and lipid bodies within the embryo proper. The optimum time for asymbiotic seed germination was obtained from immature seeds at 150 DAP. At this stage, the embryo proper reached its maximum size, and the seedcoat became dehydrated and gradually shrunk into a thin layer. By 180 DAP, seed germination declined sharply as seed approached maturity. Mature seeds pretreated with ultrasound (45 min), 1% NaOCl (45 to 60 min), or 1N NaOH (45 min) were effective in improving the germination percentage and lowering seed ABA concentrations. Our results suggest that high concentrations of endogenous ABA in orchid seeds may play a critical role in arresting embryo growth and in preventing seed germination.
This investigation documents the key anatomical features in embryo development of Cypripedium formosanum Hayata, in association with the ability of embryos to germinate in vitro, and examines the effects of culture media and seed pretreatments on seed germination. A better understanding of zygotic embryogenesis for the Cypripedium L. species would provide insights into subsequent germination events and aid in the in vitro propagation of these endangered species. In seeds collected at 60 days after pollination (DAP), soon after fertilization, no germination was recorded. The best overall germination was found at 90 DAP (≈70%), at which time early globular to globular embryos with a single-celled suspensors can be observed. After 135 DAP, the seeds germinated poorly. At this time the inner integument shrinks and forms a tight layer, which encloses the embryo, the so-called “carapace.” Using Nile red stain, a cuticular substance was detected in the carapace, which may play a role in the impermeability of the mature seed and may help the seeds survive in the stringent environment. At maturity (after 210 DAP), the embryo proper has an average size of eight cells along its length and six cells across the width. Lipids and proteins are the main storage products within the embryo. To improve seed germination, experiments were conducted to test the suitability of various media and pretreatments of seeds. When different media were used, except for the Harvais medium at 120 DAP, there was no significant difference in seed germination at three different developmental stages tested. Soaking mature seeds in 1% NaOCl or treating them with ultrasound may slightly increase the germination percentage. For seed germination, our results indicate that the timing of seed collection outweighs the composition of medium and the seed pretreatments.
Germ tube, appressorium, and subcuticular hypha development were analyzed on host and nonhost leaves for Cladosporium caryigenum (Ell. et Lang. Gottwald), the fungus causing scab on pecan [Carya illinoinensis (Wangenh.) C. Koch]. Plant features characterized for supporting fungal growth were genotype, adaxial and abaxial leaf surfaces, and leaf maturity. Germ tubes and appressoria developed on all plant leaves, despite genotype, leaf surface, or maturity. Germ tube frequency on the susceptible host, `Wichita', was lower than on the resistant host, `Elliott', but was not significantly different from the nonhost, tobacco (Nicotiana tabacum L.). Appressoria formed with equal frequency on leaves of both pecan cultivars and tobacco. Adaxial and abaxial leaf surfaces were not different within any given genotype for supporting fungal development. Immature leaves of `Elliott', but not of `Wichita', had a higher frequency of germ tubes and appressoria than mature leaves. Subcuticular hyphal development occurred only on immature leaves of susceptible `Wichita' pecan. Hence, subcuticular hyphal development is a prime candidate for being the fungal stage specific for host susceptibility. Resistance to C. caryigenum infection appears to be expressed at the plant site beneath the cuticle as fungal hyphae did not develop in a resistant pecan genotype or on nonhost leaves. Thus, resistance to the fungus causing pecan scab likely is expressed after both germ tube and appressorium development and operates beneath, not on the surface, of the leaf cuticle. Furthermore, technology developed to make these assessments would be adaptable in pecan breeding programs to screen for scab resistance.
A calcined shale potting medium is useful to obtain intact root systems free of substrate. Root system structure and shape is retained with minimal damage upon removal from this medium.