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In order to ascertain the role of anthocyanin content on the color and brightness of Hydrangea macrophylla sepals, anthocyanin contents of different colored sepals were measured for numerous commercial cultivars. Anthocyanin contents were primarily determined by extraction of the pigment, then measurement by differential spectrophotometry. Concentrations ranged from about 25 to over 400 μg delphinidin-3-glucoside per g of fresh sepal, with the magnitude roughly proportional to the perceived intensity of sepal coloration for that Hydrangea macrophylla cultivar. However, the anthocyanin content was independent of the sepal color, being the same for red, purple, or blue sepals of the same cultivar. Even though significant sepal-to-sepal variation in color intensity existed within a single inflorescence, the extractable anthocyanin content was constant for a specific cultivar. Accordingly, Hydrangea macrophylla cultivars were classified in terms of their color brightness or anthocyanin content in sepals as blush (very light colored, 25 to 60 μg·g−1), cold-hardy (light colored, 80 to 120 μg·g−1), classic (medium colored, 140 to 190 μg·g−1), vivid (deep colored, 230 to 270 μg·g−1), or vibrant (very deep colored, >300 μg·g−1) at peak bloom. The anthocyanin content of the sepals steadily increased as the inflorescence approached peak bloom, remained constant for a week or more, then decreased. The cultivar-dependent anthocyanin contents of the sepals can be used, in part, to rationalize the relative bluing capability of the various Hydrangea macrophylla cultivars.

Powdery mildew, Erysiphe polygoni DC, can be a significant problem on Hydrangea macrophylla (Thunb.) Ser. in the landscape in late summer to fall and during greenhouse propagation or production of potted plants. Because very little information related to sources of resistance is available, 90 H. macrophylla cultivars were evaluated for resistance to powdery mildew over a 3-year period. This included 69 H. macrophylla ssp. macrophylla and 18 H. macrophylla ssp. serrata (Thunb.) Makino cultivars, along with three cultivars that are hybrids between the two subspecies. Significant differences among cultivars to powdery mildew were found in all three study years. Three cultivars, ‘Amagi Amacha’, ‘Shirofuji’ and ‘Veitchii’, were among the most resistant each year. ‘Diadem’, ‘Komachi’, and ‘Omacha’ were highly resistant in 2006 and 2008, but only moderately resistant in 2007. ‘Komachi’ and ‘Shirofuji’ were considered unsuitable for breeding purposes as they do not appear to produce fertile flowers. ‘Veitchii’ was the only member of H. macrophylla ssp. macrophylla with a high level of powdery mildew resistance; while all other resistant cultivars were members of H. macrophylla ssp. serrata, not all members of this subspecies are resistant. Results of this study will be useful in breeding powdery mildew resistant H. macrophylla.

Hydrangeas are popular seaside plants; however, other than in anecdotal reports, there are no studies measuring their relative tolerance to salt spray. We examined response of ten cultivars and one subspecies of Hydrangea representing five species to foliar-applied salt solutions to recommend selections for seaside landscapes. Objectives were to determine whether there are differences in responses to salt spray among cultivars and species, and to determine whether varying concentrations of sodium chloride differentially damaged the plants. Plants were treated with a full-strength (ion concentration approximate to seawater) salt solution, a half-strength salt solution, or a control of tap water. Plants were rated after seven once-weekly applications based on percentage necrotic leaf area, an aesthetically and physiologically important symptom of damage. Cultivars of Hydrangea macrophylla and Hydrangea serrata were more tolerant of full-strength salt spray than cultivars of H. paniculata, H. anomala and H. arborescens. At half strength but not full strength, H. anomala ssp. petiolaris was most tolerant. Hydrangea macrophylla and H. serrata were the second most tolerant of half-strength applications. Hydrangea macrophylla or Hydrangea serrata should be planted where maritime salt spray will occur.

Seed germination was optimized for ten Hydrangea macrophylla (Thunb.) Ser. and two Hydrangea paniculata Siebold cultivars in vitro. Methods were also developed to assay seed physiology. Best results for in vitro study were obtained with 0.5× Gamborgs solid media in conjunction with Plant Preservative Mixture (PPM), and by sterilizing seed with trichloro-s-triazinetrione (Trichlor). Assays of physiology were conducted by sterilizing seed and treating with combinations of white and red light, cold-treatment, gibberellic acid and potassium nitrate, and light cycles. Estimates of seed viability/dormancy, germination of non-dormant seed, and germination overall were calculated for each treatment combination. The most favorable conditions for overall Hydrangea seed germination were cold-treatment for 6 weeks, imbibition with GA3 + KNO3, and plating on half-strength Gamborgs media supplemented with GA3 in the presence of white light.

A lack of adequate watering reduces the shelf life of many ornamental plants during retail. Our goals were to determine whether sprays or drenches with abscisic acid (ABA) can reduce transpiration and extend the shelf life of hydrangea (Hydrangea macrophylla). During the first 5 days after treatment, ABA drenches of 125 to 1000 ppm reduced stomatal conductance (gs) by 50 to 80% as compared to water. ABA-induced stomatal closure reduced plant water uptake from the substrate; control plants took up half of the plant-available water during the first 7 days after treatment, while it took 14 days for plants drenched with 1000 ppm to take up half of the available water. Control plants wilted after 12 days and time to wilting of drenched plants increased with increasing ABA concentrations, up to 23 days in the 1000 ppm treatment. Spray treatments had little effect on gs and no detectable effect on water uptake or time to wilting. Some yellowing of older leaves was seen with ABA drenches of 500 or 1000 ppm. Despite this side effect, ABA drenches have potential to extend the shelf life of hydrangeas in retail environments.

An experiment was conducted in 2005 and repeated in 2006 to determine the influence of mulch products and controlled release fertilizer (CRF) placement on irrigation and nutrition requirements of container-grown crops. Hydrangea (Hydrangea macrophylla ‘Fasan’ and ‘Endless Summer’) were grown in 2.7 liter (#1) containers with CRF placed above or below the mulch. Non-mulched controls were also maintained. Mulch products included geotextile discs, coco discs, plastic discs, hazelnut shells, sawdust, Biotop, and crumb rubber. Hydrangea growth, plant quality, foliar color, and foliar nutrition were measured, as well as water loss from containers. Controlled release fertilizer placed below mulch resulted in larger plants with higher quality ratings and foliar N levels compared to CRF placed above the mulch, and similar or superior size, quality and foliar N compared to non-mulched containers. After correcting for differences in plant size, there were few and minor differences in water loss from hydrangea between mulched and non-mulched containers.

Efficacy of azoxystrobin (Heritage 50W™) was assessed over a range of application rates and intervals for the control of powdery mildew (Erysiphe polygoni) and Cercospora leaf spot (Cercospora hydrangea) on bigleaf hydrangea (Hydrangea macrophylla) ‘Nikko Blue’. Rooted hydrangea cuttings were transplanted in a pine bark/peat mixture. In 1998 and 1999, azoxystrobin at 0.16 g ai/liter and 0.32 g ai/liter, as well as 0.24 g ai/liter myclobutanil (Eagle 40W™) and 0.84 g ai/liter thiophanate methyl (3336 4.5F™), greatly reduced the incidence of powdery mildew compared with the untreated control where 75% of the leaves of were infected by the causal fungus. When applied at 1-, 2-, and 3-week intervals, both rates of azoxystrobin were equally effective in both years in preventing the development of powdery mildew on bigleaf hydrangea. In 1998, all fungicides except for thiophanate methyl protected bigleaf hydrangea from Cercospora leaf spot. In the last two trials, the incidence of powdery mildew increased significantly as the application rate for azoxystrobin decreased from 0.16 to 0.04 g ai/liter and the application interval was lengthened from 1 to 3 weeks. In general, all rates of azoxystrobin applied on a 3-week schedule failed to provide the level of powdery mildew control needed to produce quality bigleaf hydrangea for the florist and landscape market. When applied at 2-week intervals, myclobutanil was equally or more effective in controlling powdery mildew than any rate of azoxystrobin applied on the same schedule. When compared to the untreated controls, significant reductions in the incidence of powdery mildew on bigleaf hydrangea were obtained with weekly applications of paraffinic oil. No symptoms of phytotoxicity were associated with the use of any of the fungicides screened.

Hydrangeas are an increasingly popular group of shrubs which are prized for their showy inflorescence. Nursery crop producers grow numerous hydrangea varieties for the landscape and florist markets. Hydrangeas are typically hand-pruned during propagation and production to promote compaction and to increase the number of branches which has potential for increasing blooms and marketability. Identifying a plant growth regulator (PGR) treatment that effectively improves the architecture of hydrangeas became an IR-4 Project research priority for 2011. Research evaluating Augeo (dikegulac sodium), Configure (benzyladenine) and Florel (ethephon) shows worthwhile results. Augeo (800 and 1600 ppm) significantly increased branching compared to untreated pots of florist varieties Hydrangea macrophylla ‘Merritt's Supreme’ and landscape varieties H. macrophylla ‘Nikko Blue’ and H. paniculata ‘Limelight’. Configure (300 ppm and 600 ppm) and Florel (500 and 1000 ppm) did not significantly improve branching in five of six trials compared to the control. Significant chlorosis on Augeo treated plants was observed initially but this diminished by 6 weeks after treatment (WAT) for four out of six trials. Little to no crop injury was observed with Configure or Florel treatments to hydrangea liners. This research shows promise for identifying a plant growth regulator treatment to meet the demand for improved branching on hydrangea.

Randomly amplified polymorphic DNA (RAPD) markers were used to distinguish five remontant and two cold-hardy Hy- drangea macrophylla (Thunb.) Ser. taxa. Eleven primers generated sufficient polymorphisms to separate these seven culti- vars into two groups. One group contained 'Penny Mac', 'Dooley' and 'Nikko Blue', while the remaining taxa, 'David Ramsay', 'Endless Summer', 'Decatur Blue' and 'Oak Hill' were clustered in the second group. All hydrangea cultivars examined are closely related; the most divergent cultivars exhibited 88% similarity based on RAPD markers. Index words: RAPD (randomly amplified polymorphic DNA) markers, Hydrangea, remontant. Species used in this study: Hydrangea macrophylla. Chemicals used in this study: Tris(hydroxymethyl)aminomethane (Tris), borate (boric acid), ethylenediaminetetraacetic acid (EDTA). Abstract Two experiments were conducted to develop a protocol for propagation of Castanopsis sclerophylla (Lindley & Paxton) Schottky by stem cuttings. In the first experiment completed in 2000, stem cuttings were taken on three dates representing three growth stages (softwood, semi-hardwood, or hardwood). Semi-hardwood and hardwood cuttings were treated with 0, 2500 (0.25%), 5000 (0.5%), 7500 (0.75%), or 10,000 (1.0%) ppm of the free acid of indolebutyric acid (IBA) dissolved in 50% isopropyl alcohol, whereas softwood cuttings were treated with the same concentrations of the potassium (K) salt of IBA (K- IBA) dissolved in distilled water. Cuttings were placed in a raised greenhouse bench and rooted under intermittent mist. Cuttings taken at the semi-hardwood and hardwood stages began to drop their leaves after approximately 2 weeks and the majority eventually died, with negligible rooting of surviving cuttings. The response of the softwood cuttings to K-IBA was quadratic with the greatest rooting (63%) at 7500 ppm K-IBA. Seventy softwood cuttings that rooted were potted for obser- vance of overwinter survival. Of these, 90% produced a flush of growth during the summer, with 80% overwinter survival. In the second experiment conducted in 2001, semi-hardwood cuttings were taken and treated with 0, 2500 (0.25%), 5000 (0.5%), 7500 (0.75%), or 10,000 (1.0%) ppm K-IBA and placed in a raised greenhouse bench with intermittent mist for rooting as in the first experiment. Results were similar to the semi-hardwood cuttings treated in the first experiment with the free acid of IBA, indicating semi-hardwood cuttings do not root and that the auxin and/or isopropyl alcohol were not toxic to the cuttings.

The flowering performance of 21 Hydrangea macrophylla cultivars was evaluated for three years at two locations. Ten plants of each cultivar were planted during 1997 in field plots at McMinnville, TN (USDA hardiness Zone 6b), and New Franklin, MO (USDA hardiness Zone 5b). The number of inflorescences was recorded every two weeks from May through September in 1999, 2000 and 2001. Daily maximum and minimum temperatures were recorded from October 1998 through September 2001. Differences among cultivars were found all three years at McMinnville and in 1999 and 2000 in New Franklin. While rankings of cultivars for number of inflorescences differed among years and locations, ‘All Summer Beauty’ and ‘Nikko Blue’ were consistently among the best performing cultivars. ‘Blauer Prinz’, ‘Blue Wave’, ‘Mariesii’ and ‘Todi’ flowered poorly all 3 years at both locations. No cultivar flowered reliably all three years of the study. Although some cultivars flowered sporadically throughout the summer, no remontant cultivars were identified. Poor flowering performance during the study appeared to be related to damage to aboveground portions of plants from a combination of early fall freezes, low winter temperatures and late spring freezes.

Nine Hydrangea macrophylla (Thunb.) Ser. and one H. serrata (Thunb. ex J.A. Murr.) Ser. cultivars were evaluated for midwinter cold hardiness, acclimation, and deacclimation to identify cultivars with increased cold tolerance. Hydrangea macrophylla ‘Endless Summer’, ‘Mariesii Variegata’, and ‘Veitchii’ acclimated later than all other cultivars. ‘Générale Vicomtesse de Vibraye’ acclimated first, and was cold hardy to −6C (21F) by September 28, 2000. The greatest cold hardiness in all cultivars occurred on January 5, 2001. Maximum cold tolerance in all cultivars was within a 6C (11F) range with ‘Endless Summer’ being the least cold hardy [−18C (0F)], while ‘Dooley’, ‘Générale Vicomtesse de Vibraye’, ‘Mme. Emile Mouillère’, and H. serrata ‘Bluebird’ possessed the greatest cold hardiness [−24C (−11F)] on January 5. Deacclimation in all cultivars began after the January 5 collection date as indicated by the February 1, 2001, data. On March 1,2001, ‘Ayesha’ and ‘Mariesii Variegata’ survived only 4C (39F) while all other cultivars survived at least −6C (21F).

An interspecific hydrangea breeding project with the goal of producing cold-hardy hydrangeas with brightly colored flowers was initiated in 1997. The objective of the current study was to transfer Hydrangea macrophylla x H. paniculata plants obtained using ovule culture to in vivo conditions and to verify their hybrid nature. Putative hybrids, representing five H. macrophylla x H. paniculata cultivar combinations, were propagated and rooted in vitro. ‘Kardinal’ x ‘Brussels Lace’ putative hybrids were the only plants that produced roots and survived transfer to the greenhouse. RAPD markers were used to verify hybridity in 13 of these plants, only 5 of which survived. Four of the ‘Kardinal’ x ‘Brussels Lace’ hybrids were greatly reduced in size and slow-growing, having an average height of only 6.4 cm (2.5 in) 8 months after being removed from in vitro conditions. Height, internode length, leaf length and leaf width were approximately six times greater in the remaining ‘Kardinal’ x ‘Brussels Lace’ hybrid than in the four small hybrids. All hybrids resembled H. paniculata in leaf shape and pubescence, and appeared to be less susceptible than H. macrophylla to powdery mildew. Intercrosses between hybrids and backcrosses to parental species will be made when the hybrids flower.

Improvement in cold-hardiness is needed in bigleaf hydrangea (Hydrangea macrophylla). Potential sources of cold-hardiness for enhancing the usefulness of this popular shrub include panicle hydrangea (H. paniculata), smooth hydrangea (H. arborescens), and oakleaf hydrangea (H. quercifolia). The objective of this study was to investigate the possibility of creating hybrids between these three species and H. macrophylla. In addition, self-compatibility of each of the species was evaluated to determine the need for emasculation when making controlled pollinations. Numerous cultivars of the species were utilized in both the self-pollination and interspecific hybridization studies. Number of flowers self-pollinated ranged from 1000 in H. arborescens to 3000 in H. quercifolia. Viable seeds were obtained from all species except H. arborescens. All five of H. quercifolia, 9 of the 18 H. paniculata, and 1 of the 8 H. macrophylla self progeny obtained survived. Emasculation of Hydrangea flowers to be used in controlled pollinations is therefore recommended. Seedlings were obtained from all interspecific crosses in which H. macrophylla was used as the maternal parent. All putative hybrid seedlings died either at the cotyledonary stage or while the first set of true leaves was expanding.