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Lisa Alexander

Hydrangea macrophylla (Thunb.) Ser., florist’s or bigleaf hydrangea, is the most economically important member of the Hydrangea genus, which accounted for over $120,000,000 in U.S. nursery sales in 2014. Both diploid and triploid H. macrophylla cultivars exist and there is some evidence that triploidy leads to larger plant and floral structures. The diploid cultivar, H. macrophylla ‘Trophee’, was previously shown to have a bimodal pollen size distribution which may be indicative of unreduced gametes. We used H. macrophylla ‘Trophee’ as a parent in a series of crosses with other diploid H. macrophylla cultivars. The objective of this study was to evaluate reciprocal full-sibling H. macrophylla families for ploidy and phenotype, determine the impact of ploidy on phenotype, and determine the efficacy of unreduced gamete breeding. Diploids and triploids were found in the offspring pool with mean 2C genome sizes of 4.5 and 6.7 pg, respectively. All offspring from crosses with ‘Trophee’ as the female parent were diploid as expected. The full-sibling family with ‘Trophee’ as the male parent contained 94% triploids, supporting the hypothesis that the bimodal pollen size distribution of ‘Trophee’ reflects the presence of unreduced male gametes. Triploids had fewer, wider inflorescences than diploids. The stems of triploids were 16% thicker and their leaves were 20% larger than those of diploid full and half-siblings. Triploids had significantly larger stomata (9.0 μm 2) than diploids (5.9 μm 2). These results establish a link between ploidy and phenotype in plants of similar genetic background and support the efficacy of unreduced gametes in polyploidy breeding.

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Cecil Pounders, Sandra Reed and Margaret Pooler

Crapemyrtle (L. indica and L. indica × L. fauriei hybrids) is one of the most popular flowering landscape plants in the U.S. Although many cultivars have been developed through breeding efforts, little has been published on the reproductive biology of the genus. The objective of this study was to evaluate barriers to successful self-seed production in crapemyrtle. Self-compatibility was assessed by comparing pollen tube growth, fruit and seed production, and seed germination following controlled self- and cross-pollinations. Observations of pollen tube growth at intervals up to 24 hours after self- and cross-pollination indicated no barriers to self-fertilization acting at the stigmatic or stylar level in L. indica, L. fauriei or cultivars derived from inter-specific hybrids of these two species. Self-pollinations of `Catawba', `Whit IV', `Tonto' and `Tuscarora' had lower percent seed pod set and seed germination than did cross-pollinations of these cultivars. The number of seeds per pod was lower when `Catawba', `Whit IV' and `Tuscarora' were self-rather than cross-pollinated, but no difference between `Tonto' self- and cross-pollinations was observed. When decreased pod set is combined with much lower seed germination for self-pollinations, selfing of crapemyrtle is extremely unproductive when compared to cross-pollination. A late-acting self-incompatibility system or inbreeding depression is indicated for L. indica and inter-specific crosses with L. fauriei.

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Zhanao Deng, Brent K. Harbaugh and Natalia A. Peres

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Zhanao Deng and Brent K. Harbaugh

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Brent K. Harbaugh, B.D. Miranda and G.J. Wilfret

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Lisa W. Alexander, Anthony L. Witcher and Fulya Baysal-Gurel

Witchhazel (Hamamelis sp.) cultivars are now available in an array of forms and flower colors, including several native, pollinator-friendly cultivars. However, little is known about response of witchhazel cultivars to powdery mildew (Podosphaera biuncinata) or the growth and flowering characteristics of witchhazel cultivars in a nursery field production setting. To provide growth, flowering, and disease incidence data to nursery growers, a cultivar trial including 23 cultivars of witchhazel representing five species was planted Apr. 2016 in McMinnville, TN. Plant growth, flowering density, length of bloom, and foliar disease incidence were evaluated over three growing seasons between May 2016 and Oct. 2018. ‘Zuccariniana’ japanese witchhazel (H. japonica) and ‘Sunglow’ common witchhazel (H. virginiana) showed the greatest height increase during the trial, and ‘Sunglow’ also added the most width during the trial. Cultivars with negative height or width growth included Sweet Sunshine chinese witchhazel (H. mollis) and hybrid witchhazels (H. ×intermedia) Aphrodite, Twilight, and Barmstedt Gold. Ten of the 23 cultivars experienced winter injury in the form of stem necrosis. Root crown sprouts were observed for all cultivars at least once during the trial. ‘Wisely Supreme’ chinese witchhazel had the longest bloom period, followed by ‘Westerstede’ and ‘Twilight’ hybrid witchhazels, whereas ‘Quasimodo’ vernal witchhazel (H. vernalis) had the greatest density of flowers. The hybrid witchhazel cultivars Aphrodite, Nina, and Arnold Promise and the common witchhazel cultivars Green Thumb and Sunglow were resistant to powdery mildew under trial conditions in all 3 years. ‘Twilight’ and ‘Barmstedt Gold’ hybrid witchhazel, ‘Little Suzie’ common witchhazel, ‘Wisley Supreme’ chinese witchhazel, and ‘Shibamichi Red’ japanese witchhazel were moderately resistant to powdery mildew.

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Zhanao Deng and Brent K. Harbaugh