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United States Department of Agriculture

Agricultural Research Service

Research Project: Development of Tetraploid Hydrangea Macrophylla Cultivars
2011 Annual Report

1a.Objectives (from AD-416)
The goal of this research is to develop a reliable method of producing H. macrophylla tetraploids from clonal material and then evaluate the effects of polyploidy on beneficial traits. This research will improve both landscape and florist cultivars. Several landscape cultivars with re-flowering ability have been introduced in the last five years; however, most have slender stems and irregular and often droopy inflorescences. Tetraploid versions of these cultivars might have increased stem thickness, shorter internodes, and larger flowers, and are unlikely to lose existing traits such as reblooming during the genome doubling process. We have identified more than 12 landscape cultivars that may benefit from ploidy manipulation and be quickly released as new cultivars. Alternatively, several hydrangea cultivars that are used exclusively in the landscape have traits that would be valuable for greenhouse production. Powdery mildew resistance is found in ‘Veitchii’, a lacecap cultivar with slender stems and light colored flowers. Several new cultivars with bi-colored or double flowers have been recently introduced to the U.S., but are only suited for garden use. We also propose that the most efficient method of transferring traits from landscape cultivars to those suited for pot plant production is through the development of polyploid cultivars from clonal tissues.

1b.Approach (from AD-416)
Methods using C-mitotic agents to induce tetraploidy in H. macrophylla cultivars have been explored by collaborating researcher. Oryzalin and colchicine will be applied to shoots of diploid H. macrophylla cultivars growing in a greenhouse and tested in vitro on clonally propagated shoots. Preliminary research suggests that trifluralin may also be an effective doubling agent in H. macrophylla. If desired results are not obtained, additional antimitotic chemical treatments will be used. Flow cytometry will be used to detect polyploids and results will be confirmed with root tip chromosome counts. Cultivars will be chosen for traits not available in existing triploids, such as powdery mildew resistance, remontant flowering, and unusual flower forms or colors. Polyploids obtained through the use of c-mitotic agents will be compared side-by-side to the cultivar from which they were derived. Traits that will be examined include plant size; leaf size and color; stem diameter; number, size and quality of inflorescences; flower color; and where applicable, reblooming.

3.Progress Report

This is the Final Report. The goal of this research was to develop a reliable method of producing Hydrangea macrophylla tetraploids from clonal material and then evaluate the effects of polyploidy on beneficial traits. We conducted six experiments attempting to induce polyploidy in Hydrangea macrophylla. Attempts have included an in vivo treatment to intact meristems as well as in vitro treatment of micropropagated meristems. There was higher than expected mortality during in vivo treatments based on previous studies with other taxa, therefore, treatments were reduced in severity and attempted again during 2011. Five in vitro experiments were all unsuccessful, several of which were terminated due to extensive fungal and/or bacterial contamination. Discussions with industry contacts with expertise in micropropagation of bigleaf hydrangea have indicated that intercellular bacteria are difficult to control during in vitro handling. Protocols for increasing ploidy in Hydrangea macrophylla were successfully developed but intact tetraploid plants were not generated during the timeline of this agreement. The ADODR or designated representative met regularly with the cooperating scientist.

Last Modified: 8/27/2015
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