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  • Author or Editor: S.E. Schlarbaum x
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Progeny from two open-pollinated mother trees were grown for 1 year in a commercial tree nursery in Murphy, N.C. Shade cloths were applied to one half of the seed plots from each mother tree and the other half were exposed to full sunlight. Seedlings were fertilized throughout the growing season to increase growth performance for better discernment of progeny and shade effects. Seedlings in shaded plots were significantly taller and had larger root collar diameters (RCD) than unshaded seedlings. An interaction between progeny and shade effects on first-order lateral root number indicates that genetic or other unknown factors were affecting the seedlings' response to changes in light. Results indicate that the use of shade cloths in nurseries may improve seedling quality of 1-0 sugar maple in the southern portion of the species range.

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A series of experiments was conducted with flowering dogwood (Cornus florida L.) to evaluate in vitro pollen germination both prior to and following storage at various temperatures. For all experiments, pollen was germinated on an agar-solidified medium containing 20% sucrose. Collection method had a significant effect on germination of `Cherokee Chief', `Cherokee Princess', and `Cloud 9' pollen. Pollen obtained from anthers that had been collected prior to dehiscence and allowed to air-dry for 24 hours had a higher germination rate than did pollen that had undergone a desiccation treatment. None of the treated pollen tested, however, had a germination rate >25% of that of freshly collected pollen. The deleterious effect of dehydration could not be reversed by rehydration. Pollen germination was tested after 1, 4, 7, and 108 days at 5, –20, and –196 °C. Pollen stored at –196 and at –20 °C had a better germination rate than that stored at 5 °C. Germination was not significantly affected by length of storage, nor was there any significant temperature × length of storage interaction.

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Development of Cornus florida L. pollen was monitored using standard paraffin histological techniques and light microscopy. Terminal buds (putative floral buds) were collected over a 6 weeks from mature landscape trees located on The Univ. of Tennessee Agricultural Campus, Knoxville. Examination of samples taken at 3- to 7-day intervals revealed variations in development representing 1- to 2-week differences between florets in a single inflorescence, florets on the same tree, and florets from different trees. Floral initiation occurred before 19 July in the 2 years of this study. Pollen development followed typical angiosperm stages: tapetal cells were multinucleate, pollen tetrads were tetrahedral, and meiosis occurred late in the developmental period. Pollen grains appeared morphologically mature by early September in both years.

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DNA amplification fingerprinting (DAF) was Used to characterize both parents (different cultivars) in breeding experiments with Cornus florida. Putative hybrids were fingerprinted and true crosses identified by finding unique male parent products in amplification profiles. Both manual and honey bee mediated pollinations successfully produced hybrid seed. Axillary buds from seedlings were used to initiate proliferating shoot cultures on woody plant medium with 4.5 μm BA. Initiation and development of adventitious roots were dependent on IBA (4.1 μm), sucrose (0–2%), and agar (0.2–0.6%) concentrations. About 40–50% of the microshoots produced roots and were acclimatized to greenhouse conditions. Cultures have been maintained without loss of regeneration potential for over 2 years. Clonal material can be reentered into the breeding program or used to evaluate horticultural characteristics in different environments and locales.

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Hand pollinations and honey bees were used to cross Cornus florida cultivars in a series of experiments investigating dogwood pollination biology from a breeding viewpoint and testing the use of insects (domestic honey bees and ladybug beetles as pollinators in dogwood breeding. Experiments were conducted to study possible incompatibility between dogwood cultivars and to determine if self-compatibility and self-fertility occur in Cornus florida. Since 1993, ≈200 seedlings have been produced by hand and insect-mediated pollinations. Honey bees can be used in dogwood breeding. Trees cross pollinated by ladybeetles had lower fruit set than trees cross pollinated by honey bees. Greenhouse forcing to accelerate anthesis and cold storage to delay the onset of bloom of container-grown trees can extend the dogwood breeding season effectively.

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