Observations on Seedling Populations of Rhododendron mucronulatum Turcz
Edward J. Garvey & Barbara L. Bullock
U.S. National Arboretum Washington D.C.
Seedlings of Rhododendron mucronulatum grown from seed collected from indigenous populations in South Korea in 1984 and from two different white flowered plants in 1985 were established in an un-replicated test plot at the U.S. National Arboretum. Observations were made in the spring and fall of 1990 and 1991 for the following characteristics: flower color, relative flower size and shape, plant size, plant form, leaf color, fall foliage color, relative time of leaf coloring, leaf shape, and leaf abscission in the fall.
Photo by Edward Garvey
Nine white flowered seedlings were found in the open pollinated population of 116 plants from R. mucronulatum f. albiflorum NA 57105. No white flowering seedlings were found in the other population of R. mucronulatum f albiflorum (N A 56379) nor the wild collected South Korean populations. There was much variation in all the characteristics evaluated. Particularly attractive was the deep red fall color of some of the seedlings. Time of leaf coloration was also quite variable, some leaves turning bright red in September and some not until December. The population from NA 57105 had a number of seedlings which retained many of their leaves all winter, but both observation years had mild winters. Only one seedling had true pink flowers. The flower color of all other plants (except the white seedlings) were shades of lavender. Seedlings from population NA 56379 were uniformly upright, tall growing, and early flowering. Two seedlings from two different populations (NA 55252 and NA55248) had narrow "willow-like" leaves.
The R. mucronulatum f. albiflorum (NA 57105), was donated to the USNA by Dr. T. Tamura of Tosu City, Japan. The plant was collected in the wild by Dr. Tamura on Tsushima, Japan, and he reported it to be more tolerant of cold, drought, and seaside conditions and it rooted easily from cuttings. The other white flowered plant (NA 56379) is believed to be of cultivated origin and the open pollinated seed were donated by Professor Pyung Sub Yoon of Seoul, Korea. The other seeds were collected on the 1984 National Arboretum Cooperative Plant Exploration Trip to the northwestern coast and islands of South Korea. The Holden Arboretum in Mentor, Ohio, and the Morris Arboretum in Philadelphia, Pennsylvania, were joint participants in this trip. It is doubtful that any plants from this program will be named, but 70 selections have been transplanted to a permanent site for germplasm preservation. Small numbers of un-rooted cuttings are available to breeders, wholesale nurseries, and botanic gardens by contacting either author, or the U.S. National Arboretum's Plant Record Office.
Dr. Edward J. Garvey is the Research Leader of the Germplasm Unit at the U.S. National Arboretum, Washington, D.C.