The objectives of this study were to evaluate self-incompatibility in Hydrangea paniculata Sieb. and H. quercifolia Bartr. and to determine optimum time for pollination of these two species. Flowers from three genotypes of each species were collected 1, 2, 4, 8, 24, 48, and 72 hours after cross- and self-pollination, stained with aniline blue and observed using a fluorescence microscope. In both species, pollen germination was observed on stigmas of over half of the flowers collected 4 to 72 hours after cross- or self-pollination. Differences in pollen tube length between cross- and self-pollinated flowers were noted from 8 to 72 hours after pollination in H. paniculata and from 24 to 72 hours after pollination in H. quercifolia. By 72 hours after pollination, most self-pollen tubes had only penetrated the top third of the style but cross-pollen tubes had grown to the base of the style and entered 40% to 60% of the ovules. Stigmas of H. paniculata were receptive to pollen from anthesis to 5 days after anthesis, while stigmas of H. quercifolia were receptive from 1 to 5 days after anthesis. This study provides evidence of a gametophytic self-incompatibility system in H. paniculata and H. quercifolia. Occasional self-seed set previously observed in these species was theorized to have been due to pseudo-self compatibility.
Tim Rinehart and Sandy Reed
Hydrangea popularity and use in the landscape has expanded rapidly in recent years with the addition of remontant varieties. Most cultivars in production belong to the species Hydrangea macrophylla but H. paniculata, H. arborescens, H. serrata, H. aspera, H. heteromalla, H. integrifolia, H. anomala, H. seemanii, and H. quercifolia are also commercially available. In addition to species diversity there is high intra-species variation, particularly in H. macrophylla, which includes mopheads, lacecaps, French, Japanese, dwarf, and variegated varieties. Relatively little is known about the genetic background or combinability of these plants. DNA sequence data, genome size, RAPD, AFLP, and ISSR markers have been used for taxonomic identification and to estimate diversity within the genus. All of these methods have limited usefulness in a large scale breeding program. We recently established microsatellite markers for Hydrangea and evaluated their utility for estimating species diversity and identifying cultivars within H. macrophylla and H. paniculata. We also verified an inter-specific cross between H. macrophylla and H. paniculata using these markers. Future research includes marker assisted breeding, particularly with respect to remontant flowering traits.
Torin O. Pope and Caula A. Beyl
Agrobacterium rhizogenes is a valuable new tool for inducing adventitious roots in difficult-to-root ornamentals To evaluate species and strain interactions, three ornamental species were chosen: Hydrangea quercifolia, Pyrus calleryana, and Photinia × fraserii. Terminal shoots (2.5 cm long) were collected at bud swelling and then immersed in bleach (20% v/v) for 10 min with stirring. They were rinsed three times in sterile distilled water and cultured individually in test tubes containing 15 ml of Murashige and Skoog medium. After 3 weeks, the uncontaminated shoots were divided into five groups: four strains of A. rhizogenes and a control. There was a significant effect of strain and species in the production of callus and organs from the shoot tips. The presence of strain by host interaction was observed In the morphogenic response of explants.
Janet C. Cole, Robert O. Brown, and Mark E. Payton
and timing of effective growth regulators for a variety of woody species are needed ( Warren et al., 1991 ). Oakleaf hydrangea is an important container crop for many nurseries in the southern and midwestern United States. It is used in the landscape
Sandra M. Reed and Lisa W. Alexander
Oakleaf hydrangea ( Hydrangea quercifolia Bartr.; Hydrangeaceae) is a woody shrub native to the southeastern United States, where it grows in calcareous soils in the understory of open woodlands ( McClintock, 1957 ). There are ≈70 species in the
Jyotsna Sharma and Jim Rich
Plants infected with Meloidogyne spp. (root-knot nematodes) often are stunted and lose aesthetic value due to chlorosis, wilting, and leaf margin necrosis. We assessed reproduction of three root-knot nematode species, Meloidogyne arenaria, M. incognita, and M. javanica, on five plant taxa native to the southeastern U.S. The plant taxa included were: Hydrangea quercifolia `Oakleaf', Viburnum obovatum `Densa', Itea virginica `Little Henry', Illicium parviflorum, and Clethra alnifolia `Ruby Spice'. Three commonly grown non-native shrubs, Ligustrum japonicum `Texanum', Ilexcrenata `Compacta', and Buxus microphylla `Wintergem', also were included in the study to serve as susceptible, positive controls. Highest gall rating (10) was observed on roots of I. crenata `Compacta' infected with M. incognita, but highest number of eggs (6397 eggs/g of roots) was observed in plants of this cultivar inoculated with M. javanica. Few or no galls were observed on roots of the five native plant taxa, and nematode eggs were recovered only from roots of I. virginica `Little Henry' inoculated with M. arenaria and M. javanica (13 and 20 eggs/g of roots, respectively). Fresh weights of shoots or roots were not affected by nematode inoculation. Due to lack of root gall development and little or no reproduction on the native taxa, we conclude that these are resistant or immune to the three species of Meloidogyne and might be suitable for planting in infested soil.
Sandra M. Reed
Oakleaf hydrangea ( Hydrangea quercifolia Bartr.; family Hydrangeaceae Dumort.) is an ornamental shrub that is native to the southeastern United States ( McClintock, 1957 ). Most plants grow 2 m or taller in height with an equal to wider spread
Xingbo Wu and Lisa W. Alexander
). Five species of Hydrangea ( H. macrophylla , H. paniculata , H. quercifolia , H. arborescens , and H. anomala ssp. petiolaris ) are widely cultivated in the United States as landscape plants ( Dirr, 2009 ). Among them, H. macrophylla , also
Joshua H. Kardos, Carol D. Robacker, Michael A. Dirr, and Timothy A. Rinehart
Nursery Assn. Res. Conf. 51 570 572 Kudo, N. Kimura, Y. Niimi, Y. 2002 Production of interspecific hybrid plants by crossing Hydrangea macrophylla f. hortensia (Lam.) Rehd. and H. quercifolia Bartr. through ovule culture Hort. Res. Japan 1 9 12 Kudo
Ming Cai, Ke Wang, Le Luo, Hui-tang Pan, Qi-xiang Zhang, and Yu-yong Yang
The genus Hydrangea is one of the most popular ornamental flowers because of its large and showy inflorescences. The genus comprises at least 30 taxa with centers of diversity in eastern Asia, eastern North America, and South America ( Kardos et