Up-date on the Red maximum from Mount Mitchell
August E. Kehr
Hendersonville, North Carolina
This article discusses a new theory to explain the cause of the mysterious red colored Rhododendron maximum that grows wild in the area of Mount Mitchell in the western part of North Carolina (Kehr 1994) and suggests the unusual red color may be brought about by the action of a movable (transportable) gene.
In the report written in 1994, it was suggested that the unusual red color of the mysterious red maximum from Mount Mitchell, North Carolina, was the result of a somatic chimera, based on a consideration of five possible explanations for the source of the red color. These considerations were:
1. Is it a hybrid?
2. Is the effect caused by some plant pathogen?
3. Is it caused by some physiological factor?
4. Is it caused by movable genes?
5. Is it caused by a chimera?
Of the above it was concluded in 1994 that no one guess (hypothesis) of the cause was entirely satisfactory in explaining the mysterious and unusual color behavior and color patterns in the red maximum. However, based upon evidence available at the time, it was concluded that the color behavior most nearly fit an explanation of a chimera. A chimera is defined as a plant composed of two or more genetically distinct tissues. As such it is propagated by cuttings, grafts air layers or other similar vegetative means.
Plants vegetatively propagated from the same one collected by Mr. Joe Gable from Mount Mitchell over 50 years ago are growing, in addition to my own garden, in the Rhododendron Species Botanical Garden in Federal Way, Wash., and the gardens of Dr. Harold Crutcher in Asheville, N.C., Capt. Dick Steele in Nova Scotia, the late Caroline Gable in Pennsylvania, George Ring in Virginia, and Polly Hill on the island of Martha's Vineyard, Massachusetts. In my garden the red color appeared at random or in various parts of the plant, but was never permanently located at any one location on the plant. In addition, the flower color was variable in that the individual florets could be all red, or combinations of red and white. The latter included picotee, white throats and red on the outside rims of the petals, red throats with white on the outside rims of the petals. The affected stems could be beet red in their entire diameter, or partially red in their diameters. All these conditions could be explained under the description of a chimera.
Flower variations in the red R. maximum.
Photo by Polly Hill
Everything changed when a seedling grown from self-pollinated seed, taken from red flowers of a truss of the plant of red maximum, finally bloomed. The seedling produced four trusses, all four of which had white centers and red outside rims on the petals. An examination of the young stems on the newly flowering plant showed they were red completely through to the center, although one lower branch failed to be red. In summary, the plant and the four trusses that opened in 1997 showed the red color throughout with the exception of one lower branch. To identify the plant, I have tentatively given it the designation of 'Summer Joy', although it has not yet been registered as such. Seedlings of the red maximum have been grown by many other people including George Ring, Robert Gamlin, Weldon Delp, and probably others of whom I am not aware. I have given seedlings to many members of the Society.1
With the flowering of 'Summer Joy', the hypothesis of a chimera as a cause of the unusual red color had to be rejected on the grounds that the red color had been carried in the seed. To my knowledge and understanding of chimeras, the red color of a chimera would not be expected to be transmitted by means of true seed. In order to be transmitted by seed it would be essential that the red color be passed on to its progeny through the egg and pollen cells. It is my understanding that chimeral tissues are propagated only by vegetative means and are not transmitted by means of fertilization of eggs and pollen grains. At least up the present, I cannot find any literature that indicates anything but a somatic or non-sexual manner of transmission of chimeras to the progeny of the plant.
After much deliberation, my best guess is that the red color in this R. maximum is the result of movable genes, as postulated in corn by Dr. Barbara McClintock at Cornell University and Brookhaven Laboratory and for which work she received the Nobel Prize. This movable gene theory can be described as follows. Special genes can move about on the chromosomes in the process of egg and pollen cell formation and come to rest at unpredictable locations on the chromosomes. When the gene comes to rest at a more or less random location, it causes the genes adjacent to it to mutate. Thus plants, such as 'Summer Joy', will not be stable. When the movable gene moves to another location, the adjacent mutated genes return to their original expression. As a result, such plants that have movable genes in their genetic make-up may mutate more or less at random depending upon the activity of the movable genes. Only time will tell how stable or unstable 'Summer Joy' will perform. I believe it will continue to mutate just as it already has done.
To me, the movable gene hypothesis as applied to the red maximum is not quite the same in its total action as that found in corn and some evergreen azaleas. In the latter the color appears in mottles, narrow stripes, specks, and color sectors of the seed or flowers. I have similar characteristics of movable genes in progenies of azaleas found in some progenies of plants used in my long-standing project to develop a yellow flowered evergreen azalea. These are primarily stripes, specks, and segments of red in the background of cream, and thus have a somewhat different appearance than those color variants in the red maximum. I have never seen striping, tiny spots, or specks in the red maximum.
It is interesting that a very similar condition of an unstable red color appeared in peaches (Chaparro, Werner, Whetten, and O'Malley 1995). These authors also concluded that the unstable red color was the result of a movable gene. They self-pollinated different sectors of the plant and were able to develop red colored individuals that showed no instability.
In conclusion, there is need for more study of the red maximum and its nature. The observations made here, and previously, do not provide conclusive evidence of the nature of the red color in these plants, nor of its inheritance. It is my hope that some student or scientist will conduct some comprehensive research on this problem. It is very probable a grant to conduct such research would receive high priority by the trustees of the ARS Research Foundation or even the Horticulture Research Institute.
In addition, there may be others who have grown, or are growing seedlings. I urge such persons to report their observations and results in short notes to the editor of our Journal. Like the work on peaches, it is probable red colors could be developed that are no longer unstable.
Chaparro, J.X., D.J. Werner, R.W. Whetten, and D.M. O'Malley. 1995. Characterization of an unstable anthocyanin phenotype and estimation of somatic mutation rates in peach. Jour. HeredityVol.86:83-193.
Kehr, A.E. 1994. The mysterious red maximum from Mount Mitchell. J. Amer. Rhod. Soc. Vol. 48(1):31-37,47.
1 Dr. Kehr is willing to send seed of the red maximum to anyone who wishes to conduct further research as that done by Dr. Werner on peaches, i.e., selfing the different sectors in an effort to "fix" them in a stable condition.
Dr. August Kehr is a member of the Southeastern Chapter and a frequent contributor to the Journal.