Horticultural Reviews, Volume 49. Группа авторов

μM TDZ) are recommended to produce a moderate number of adequately elongated shoots (Ledbetter and Preece 2004). Additionally, inclusion of gibberellic acid in the medium can enhance shoot elongation when higher cytokinin concentrations are used (Sebastian and Heuser 1987). It was also determined that micropropagated shoots have a high ability to root; on average 93%. Sebastian and Heuser (1987) demonstrated that shoots derived from callus tissue had a greater ability to root than shoots derived directly from dormant buds; this difference was attributed to increased juvenility in the callus derived shoots. Conversely, Kästner et al. (2017) reported that tissue cultures of H. quercifolia declined in vigor after many repeated subcultures, and that it was necessary to reestablish explants periodically. Cochran et al. (2014) found significant (but inconsistently) improved branching and symmetry in container‐produced H. quercifolia ‘Alice’ which were propagated in tissue culture, compared to cutting propagated material.

X. FUTURE PROSPECTS

      Hydrangea quercifolia is a particularly understudied and underutilized species with unique horticultural potential. Because it is unrivaled among hydrangeas for its year‐round aesthetic value and intriguing foliar characteristics, it can be described as “a shrub with a difference” (Lawson‐Hall and Rothera 1995). Hydrangea quercifolia has immense potential waiting to be developed. The amount of improvement seen in H. macrophylla, H. paniculata, and H. arborescens over the previous century serves as an example of the possibilities the genus has to offer. To date, progress has been made in selecting for compactness and floral traits, however, there are other traits which would benefit from improvement.

Resistance to biotic and abiotic stressors are still a priority and have not yet received enough attention. Cold tolerance and deacclimation timing are limiting factors in cold climates. This is currently being examined in the species across its latitudinal range which will reveal the extent of cold hardiness and variation for deacclimation timing that is available for selection. Resistance to wilt and foliar pathogens still needs to be studied in order for H. quercifolia to be robust enough to survive nursery production reliably and still be attractive in the landscape with minimal pesticide applications. Tolerance to heat and direct sunlight are important traits to identify for southern growers.

      Another trait that has yet to receive any appreciable amount of attention is floral scent. The floral scent in wild oakleaf hydrangea plants is sweet and, although not strong, it is generally stronger than that of other Hydrangea species (A. Sherwood, pers. observ.). Because Hydrangea are typically not considered to possess fragrant flowers, a cultivar with a stronger fragrance would be quite significant. It is unknown what compounds make up the scent, nor what floral organs produce them. This trait would be interesting as a breeding target and likely plays a role in pollination in the wild.

LITERATURE CITED

      1 Abe, R. and K. Ohtani. 2013. An ethnobotanical study of medicinal plants and traditional therapies on Batan Island, the Philippines. J. Ethnopharmacol. 145:554–565.

      2 Alexander, L. 2017. Production of triploid Hydrangea macrophylla via unreduced gamete breeding. HortScience 52:221–224. doi:10.21273/HORTSCI11358‐16.

      3 Alonso‐Blanco, C., M.G.M. Aarts, L. Bentsink, J.J.B. Keurentjes, M. Reymond, D. Vreugdenhil, and M. Koornneef. 2009. What has natural variation taught us about plant development, physiology, and adaptation? Plant Cell 21:1877–1896. doi:10.1105/tpc.109.068114.

      4 Banks, W.H., Jr. 1953. Ethnobotany of the Cherokee Indians. Master’s Thesis, Univ. of Tennessee.

      5 Bartram, W. 1791. Travels through North & South Carolina, Georgia, East & West Florida, the Cherokee Country, the extensive territories of the Muscogulges, or Creek Confederacy, and the country of the Chactaws; containing an account of the soil and natural productions of those regions, together with observations on the manners of the Indians. James & Johnson, Philadelphia.

      6 Baysal‐Gurel, F., N. Kabir, and A. Blalock. 2016a. Foliar diseases of hydrangeas. Tennessee State Univ. Extension. p. 1–7.

      7 Baysal‐Gurel, F., N. Kabir, and A. Blalock. 2016b. Root diseases of hydrangeas. Tennessee State Univ. Extension. p. 1–4.

      8 Beck, W.T. and T.G. Ranney. 2014. Ploidy levels and interploid hybridization in panicle hydrangea (Hydrangea paniculata). SNA Research Conference 59:181–187.

      9 Beckman, T.G. and P.L. Pusey. 2001. Field testing peach rootstocks for resistance to armillaria root rot. HortScience 36:101–103.

      10 Behnke, M. 1979. Selection of potato callus for resistance to culture filtrates of Phytophthora infestans and regeneration of resistant plants. Theor. Appl. Genet. 55:69–71. doi:10.1007/BF00285192,

      11 Cerbah, M., E. Mortreau, S. Brown, S. Siljak‐Yakovlev, H. Bertrand, and C. Lambert. 2001. Genome size and species relationships in the genus Hydrangea. Theor. Appl. Genet. 103:45–51.

      12 Choi, H., T. Ito, M. Yokogawa, S. Kaneko, Y. Suyama, and Y. Isagi. 2017. Population and genetic status of a critically endangered species in Korea: Hydrangea luteovenosa (Hydrangeaceae). Korean J. Pl. Taxon. 47:1–5.

      13 Church, G. 2001. Hydrangeas. Firefly Books, Buffalo, NY.

      14 Cochran, D.R., M. Benitez‐Ramirez, and A. Fulcher. 2014. Effect of branch‐inducing treatments on growth of tissue culture and cutting‐propagated Hydrangea quercifolia ‘Alice.’ J. Environ. Hortic. 32:182–188.

      15 Collard, B.C.Y. and D.J. Mackill. 2008. Marker‐assisted selection: an approach for precision plant breeding in the twenty‐first century. Phil. Trans. R. Soc. B. 363:557–572.

      16 Cozzo, D.N. 2004. Ethnobotanical classification system and medicinal ethnobotany of the Eastern Band of the Cherokee Indians. Doctoral Thesis, Univ. of Georgia Athens.

      17 De Smet, Y., C.G. Mendoza, S. Wanke, P. Goetghebeur, and M.S. Samain. 2015. Molecular phylogenetics and new (infra)generic classification to alleviate polyphyly in tribe Hydrangeeae (Cornales: Hydrangeaceae). Taxon 64:741–753. doi:10.12705/644.6.

      18 Deans, L.E., I.E. Palmer, D.H. Touchell and T.G. Ranney. 2021. In vitro induction and characterization of polyploid Hydrangea macrophylla and H. serrata. HortScience 56:709‐715. doi:10.21273/HORTSCI15783‐21.

      19 Dirr, M.A. 2004. Hydrangeas for American Gardens. Timber Press, Portland, OR.

      20 Dirr, M.A., O.M. Lindstrom Jr., R. Lewandowski, and M.J. Vehr. 1993. Cold hardiness estimates of woody taxa from cultivated and wild collections. J. Environ. Hortic. 11:200–203.

      21 Elshire, R.J., J.C. Glaubitz, Q. Sun, J.A. Poland, K. Kawamoto, E.S. Buckler, and S.E. Mitchell. 2011. A robust, simple genotyping‐by‐sequencing (GBS) approach for high diversity species. PLoS ONE. e19379. doi:10.1371/journal.pone.0019379.

      22 Friedman, J.M., J.E. Roelle, J.F. Gaskin, A.E. Pepper, and J.R. Manhart. 2008. Latitudinal variation in cold hardiness in introduced Tamarix and native Populus. Evol. Appl. 598–607. doi:10.1111/j.1752‐4571.2008.00044.x.

      23 Funamoto, T. and M. Ogawa. 2002. A cytogeographical study in Hydrangea paniculata Sieb. (Saxifragaceae s. l.) in Japan. Chromosome Science 6:73–82.

      24 Granados Mendoza, C., S. Wanke, P. Goetghebeur, and M.S. Samain. 2013. Facilitating wide hybridization in Hydrangea s. l. cultivars: a phylogenetic and marker‐assisted breeding approach. Mol. Breed. 32:233–239. doi:10.1007/s11032‐012‐9822‐8.

      25 Greer, S.P. and T.A. Rinehart. 2009. in vitro germination and dormancy responses of Hydrangea macrophylla and Hydrangea paniculata seeds to ethyl methane sulfonate and cold treatment. HortScience 44:764–769.

      26 Gronovius, J.F. 1739. Flora Virginica. Reprinted (1946) by Arnold Arboretum, Boston, MA.

      27 Gupta, P.K., H.S. Balyan, P.C. Sharma, and B. Ramesh. 1996. Microsatellites in plants: A new class of molecular markers. Curr. Sci. 70:45–54.

      28 Hagan, A.K. and J.M. Mullen. 2001. Diseases of Hydrangea. Alabama Cooperative Extension System, Alabama A&M and Auburn Univ. p. 1–8.

      29 Hagan,