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Robert D. Marquard

Six phosphoglucomutase phenotypes were observed in pecan [Carya illinoensis (Wangenh.) K. Koch] progeny after controlled pollinations. At least one locus (Pgm-1) is present that controls polymorphism of phosphoglucomutase (PGM) isozymes in pecan. The inheritance appears simple with three observed alleles. However, progeny produced from two crosses resulted in significant deviation from the expected segregation ratios. Out of 65 named cultivars, 61 were of a single phenotype, and two of six possible phenotypes were not observed. Only one region of PGM activity was consistently expressed by gel electrophoresis from pecan tissue.

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Robert D. Marquard

More than 30 pecan [Carya illinoensis (Wangenh.) K. Koch] seedlings of `Riverside' have exhibited an unusual leaf morphology described as lace-leafed. Seedlings have relatively low vigor, compound leaves, and leaflets with deeply serrated margins with higher length: width ratios than normal seedings. Some leaves are both pinnate and palmately compound and some leaflets are lobed. The segregation ratio of lace-leafed seedlings for one gene controlling a polymorphic genetic marker supports the hypothesis that lace-leafed seedlings result from selfing of `Riverside.' Nine percent (three of 33) of seedlings derived from selfing of `Riverside' exhibited the lace-leafed morphology, suggesting a recessive trait controlled by one or two genes. The gene(s) controlling this phenotype in pecan is arbitrarily designated the ll gene(s).

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Robert D. Marquard

In vivo pollen tube growth of pecan [Carya illinoinensis (Wangenh.) K. Koch] was estimated to be ≈ 150 μm·hour-1 from 3 to 8 hours postpollination. Pollen tubes averaged 47, 194, 405, and 946 μm after 2, 3, 4, and 8 hours postpollination, respectively. Pollen tube growth was strongly influenced by temperature, and in vitro studies demonstrated pollen germination and tube growth were optimal at 27C for `Cape Fear' pecan. In in vivo studies, tubes of cross-pollen did not grow significantly faster than tubes of self-pollen. Pollen tubes of water hickory [C. aquatica (Michx. f.) Nutt.] grew significantly faster than those of C. illinoinensis. Bitternut [C. cordiformis (Wangenh.) K. Koch] and mockernut hickory (C. tomentosa Nutt.) pollen tubes grew significantly slower on pecan stigmas than did pecan pollen. Pollen arriving first on the stigma has a decided advantage for fertilization success of pecan. The fertilization success rate of pecan pollen arriving 24 hours after first pollen arrival was <3%.

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Bruce W. Wood and Robert D. Marquard

Self-pollination was estimated in three Georgia pecan [Carya illinoinensis (Wangenh.) K. Koch] orchards. Selfing in two large orchards lacking an interplanted complementary pollinizer (one orchard being comprised of `Curtis' and the other `Moneymaker') was estimated to be at least 3% and 49%, respectively. A `Cheyenne' orchard containing `Stuart' as a complementary pollinizer at 5% density was estimated to have had at least 14% and 42% of ripened nuts derived from selfing in two consecutive years. These estimates suggest self-pollination may reduce yield in pecan orchards in the southeastern United States.

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Charlotte R. Chan and Robert D. Marquard

Hamamelis cultivars are typically propagated by grafting onto H. virginiana rootstock. Grafting is labor-intensive and the understock frequently suckers which can lead to the loss of the scion. A cultivar growing on its own root system would eliminate this problem. Our research was undertaken to develop a successful method of rooting micropropagules. The source material was established cultures of H. × intermedia `Diane,' H. virginiana, and a H. vernalis selection. The rooting treatments consisted of four concentrations of K-IBA (0, 5, 10, and 20 μM) in 0.02% Tween 80. Three replicates of eight cuttings each were taken from the three sources for each of the four treatments. The cuttings were placed in 50-mL beakers, cut-end down, with 10 mL of the treatment solution. The beakers were sealed with Parafilm, and cuttings were soaked for 24 h. After treatment, the cuttings were randomly stuck into Kadon flats prepared in advance with a sterile mix of 1 peat: 1 perlite and were watered-in. Cuttings were misted, and flats were covered with plastic and Remay. They were kept in a warm (19-24 °C) greenhouse. Cuttings rooted in 3 to 4 weeks and were subsequently fertilized weekly with Peter's 20N-20P-20K at 150 ppm. At 12 weeks, data were collected for the rate of survival, height, branching, number of nodes, and root mass, and the plants were transplanted to quart pots. Ninety percent of the cuttings rooted; the most favorable response was with 10 μM K-IBA, although all treatments produced >80% rooting. This method was time and labor efficient. Moreover, micropropagation is not dependent on the season, and production of new plants could proceed on a continuous basis, making this a viable alternative to commercial grafting.

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Charlotte R. Chan and Robert D. Marquard

The Holden Arboretum, established in 1931, is the largest arboretum in the United States. Its mission is to promote the knowledge and appreciation of plants for personal enjoyment, inspiration, and recreation; for scientific research; and for educational and aesthetic purposes. Of the Arboretum's 3100 acres, 800 acres support collections and display gardens, while the balance comprise natural areas. The collections include nearly 8,000 accessions from 76 plant families; about 700 plant species, some rare or endangered, occupy the natural areas. The education component of the mission connects the Arboretum with the public through school programs, classes, horticultural therapy, and seasonal internships. Two research fellowships are also available. The Holden Arboretum has expanded the research emphasis. The David G. Leach Research Station, part of the Arboretum since 1986, focuses on rhododendron and magnolia breeding and research. Built in 1993, the Horticulture Science Center is a modern research and production facility able to more fully implement and support a broad range of formal horticultural research. The main objective of the research program is to develop superior woody ornamentals for the landscape through hybridization. Additional research emphasizes reproductive biology and using biochemical markers (isozymes and RAPDs) to answer basic questions about the genera under study (Aesculus, Hamamelis, Cercis).

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Arthur M. Richwine and Robert D. Marquard

×Chitalpa tashkentensis (Chilopsis linearis × Catalpa bignonoides) is an attractive small tree producing lavender to white orchid like flowers. Micropropagation would allow for the rapid clonal propagation of new hybrids for testing cold hardiness and landscape performance. The rapid growth response of Chitalpa shoot cultures also makes it an excellent subject for the study of in vitro growth parameters of woody plants. Shoot cultures were initiated from shoot tips on Anderson's rhododendron medium with MS vitamins, 3% sucrose, 1 μm BA, pH 5.6 and solidified with 0.6% phytagar. Shoot cultures stabilized rapidly. Two-node microcuttings were placed on modified MS media (200.1 μm Na2 EDTA and 200.5 μm FeSO47H2O), MS vitamins, 3% sucrose, pH 5.6, 0.6% phytagar and supplemented with NAA (0 0.5, 1.5, or 3 μm) in combination with BA (0, 1, 5, 10, 15, 20, 30, or 40 μm). Cultures grown on media supplemented with 1 mm BA produced the longest shoots and the most nodes per shoot. Cultures grown on media supplemented with 10 μm BA produced the most shoots. Microshoots readily rooted on plant growth regulator free MS medium and were easily acclimated.

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Robert D. Marquard and Jimmy L. Tipton

Desert willow (Chilopsis linearis) is native to the arid southwestern U.S. and is used as a landscape shrub. Catalpa (Catalpa bignonioides) is a small tree common in the southern U.S. that is used as a landscape plant. Both species have showy flowers and are members of the Bignoniaceae family. Controlled crosses were made using pollen from a single catalpa tree and desert willow stigmas of the cv. `Marfa Lace'. Fruit developed normally and seven seedlings were produced that had leaf morphology intermediate between the parents. From starch gel electrophoresis, putative hybrids had isozyme banding patterns consistent with hybridization between the parent species. A second biochemical verification is being conducted using probes for ribosomal RNA genes.

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Charlotte R. Chan and Robert D. Marquard

Traditional seed propagation (warm/cold stratification) was compared to embryo culture of Chionanthus virginicus L. to determine if germination could be promoted and time necessary to produce a sizable plant could be reduced. Embryos of C. virginicus were extracted from immature fruit collected 9, 16, and 23 Aug. 1995 and grown in vitro on Anderson's rhododendron medium. They germinated in 4 weeks and were transferred ex vitro to flats. Mature fruit from the same source were grown simultaneously using warm/cold stratification. The two groups were evaluated periodically over a 2-year period for percent germination, plant size, and seedling success. The embryo-cultured plants had a lower survival rate (16% vs. 44%) and were more labor intensive. After 2 years, embryo-cultured plants were 13.4-fold the mass and 4.7-fold taller than traditionally grown plants. Ten-month-old cultured plants were comparable in size to 2-year-old plants grown traditionally.