Logo for the Journal American Rhododendron Society

Journal American Rhododendron Society

Current Editor:
Dr. Glen Jamieson ars.editor@gmail.com

Volume 60, Number 1
Winter 2006

DLA Ejournal Home | JARS Home | Table of Contents for this issue | Search JARS and other ejournals

Nothing New Under the Sun, Part I
Donald L. Craig
Centreville, Nova Scotia

In Part I of "Nothing New Under the Sun," a letter from Clement Gray Bowers is reprinted along with comments in reference to this letter. Part II & III will be published in later issues. These will include a letter from Wendell H. Camp and a lecture by Dr. Bowers and comments on these two archival publications.

        According to Ecclesiastes "there is nothing new under the sun"; well, not entirely true, but certain nagging problems are always testing the hybridizer's fundamentals and nerves.
        Having little to do one day in January I decided to tidy up the files I had brought to my new home on Lakewood Road. In back of a file "Letters Received" I found two letters that I had not glanced at in years. They were addressed to the now late Dr. R. Bill Hunter of the Central Experimental Station in Ottawa. One was from the eminent Clement G. Bowers, Research Associate, Cornell University, and Professor of Botany, Harper College, State University of New York. Bowers was the author of Rhododendrons and Azaleas, Their Origins, Cultivation and Development. The other was from Wendell H. Camp, Curator of The Academy of Natural Sciences of Philadelphia. Of Camp, we know little, but it is obvious from his letter that he had a consummate grasp of the genus Rhododendron.
        Dr. Hunter, a plant research scientist, was interested in developing a rhododendron breeding and evaluation programme for the Ottawa area, an area noted for extremely cold winters and hot, humid summers. The letters from Bowers and Camp were responses to his letters and queries for assistance in the establishment of such a project.
        Hunter and I knew one another well through our fruit breeding research. He was also aware of the success made by our Kent ville Research Station recently established (1952) rhododendron programme. To keep me informed of his aspirations he sent me copies of the Bowers and Camp correspondence.
        I asked John Weagle to read the correspondence. Subsequently John agreed that this information was of great interest and should be shared by recording it in the RSCAR Newsletter. We believe the letters are also of historic importance and in spite of their age - 53 years - contain information that is critical to anyone interested in the problems faced by the rhododendron pioneers of the first half of the 20th century, the basis of hardiness in some lines of Eastern hardy hybrids and with aspirations similar to Hunter's, that is, breeding for a climate just north of present rhododendron territory.
        I know that the Ottawa rhododendron programme was not very successful. I have information on file showing that Larry C. Sherk, a colleague of Hunter's, did compile rhododendron plant material which he evaluated at the Central Farm. Indeed in 1966 and 1967 Kentville received surplus plants from Sherk's collection. According to the RSC Bulletin Vol. 1, No. 1 from 1973, Larry Sherk is listed as a society director. He left Agriculture Canada and joined Sheridan's Nursery in southern Ontario. He has recently retired.
        The Bowers letter is presented to you in this issue, and the Camp letter will be presented to you in a later issue. We trust they will be of interest to you. Perhaps you will agree with John and me that the problems are still quite the same, nothing terribly new in that department, just exciting new found material with which to work and some better ways of doing things. There certainly seems to be much promise ahead as great advances already have been made.
        Following the printing of each letter John will focus on the relevance of the information in the letters when viewed in today's light. We look forward to his appraisal. We are indeed fortunate to have this article appraised by three distinguished rhododendron experts Joe Harvey, Peter Tigerstedt and the late August Kehr. It is with sadness that we learned of Augie's passing just weeks after having sent his article. Our thanks go to Joe for his meticulous proofreading of the entire article as well.
        The following letter from Clement Gary Bowers, Maine, NY, was mailed October 2, 1953, and received by the Horticultural Division of the Experimental Farm in Ottawa on October 6, 1953.

Dr. A.W.S. Hunter, Principal Horticulturist,
Central Experimental Farm,
Department of Agriculture,
Ottawa, Canada.

Dear Dr. Hunter:
        At long last I am now replying to your letter of August 11th which has been awaiting a period when I had the necessary time to give you the information you needed. Even now I am not sure that I have not forgotten several important items, so that I hope that you will feel free to ask me further questions if I can be of service. Unfortunately, I have not published on a good deal of this, so that I cannot refer you to printed papers, which might have saved us both some time. I have very little on the genetical results of any of my work, although you are perhaps familiar with my book, published by McMillan in 1936 and now out of print. Sometime this fall, the Massachusetts Horticultural Society is going to print a smallish book by me on the winter-hardy rhododendrons and azaleas for sub-zero climates but this will be mainly material for the gardener rather than for the plant breeder. I shall try to let you know when this comes out.
        At the moment, I do not know what minimum winter temperatures you ordinarily expect in Ottawa, but I do know that you have sub-zero weather. I would guess that you have many times every year when the temperature goes lower than -15°F. If colder than -20°F you will find it unsatisfactory for any evergreen rhododendrons at all, as the flower buds kill at about that temperature, but it will be entirely possible for you to do well with the hardy deciduous azaleas down to -30°F or even colder. I can usually expect -20° here at my home, which stands in a "frost pocket," making it necessary for me to grow seedlings elsewhere. Only one of the Obtusum azaleas will grow here (R. poukhanense), and R. kaempferi will usually kill to the ground with prolonged temperatures of -15°. I would suspect that the Dexter hybrids and others of the Fortunei Series1, which are about the hardiest of the newer sorts, would be extremely unreliable at -15° and could be depended upon where boxwood might survive with slight protection. One might find these plants surviving one pretty cold night, but if this were repeated many times it would make a difference. Claims made for survival under sub-zero temperatures are not valid if they involve only survival under one extraordinary night. You will find many such claims in the current literature.
        There isn't much available genetical information on rhododendrons that will help with breeding for hardiness. Evidently most of the desired characters are carried as multiple factors and do not appear to segregate out easily, although I have as yet very little F2 material to base any conclusions upon. Common observations of everybody's results seems to indicate that that the "wild" or lilac color of R. catawbiense, present in varying amount in almost all of the hardy hybrids, is very hard to get rid of. I have found that even the white clones (most of which are pinkish in bud), such as 'Catawbiense Album', 'Album Elegans' and 'Boule de Neige', when inter-crossed give a preponderance of purplish or lilac colored seedlings in the F1. I think that the only chance of getting rid of this purplish tinge in Catawba hybrids is by using one of the rare white individuals found in the wild, which do not seem to transmit any purple to their seedlings. Some of these white forms were found in the Virginia mountains some years ago by Powell Glass (now deceased) of Lynchburg, Va. Gable grew seedlings of these. Also, Labar's Nursery of Stroudsburg, Pa., has a wild white individual, which they are propagating by layerage, and I have been using this in crosses, but do not have any plants near blooming size. Write to Mr. Russell Harmon of LaBar's about it; he may have a plant or two to sell you that is about to bloom. Also, you may pick up a Glass seedling from Joseph B. Gable of Stewartstown, Pa. Mrs. Glass's original plant is dead, she tells me.
        I made a lot of controlled crosses in 1926-29, then gave up all breeding work between 1930 and 1945. In these first crosses I made systematic "checkerboard" reciprocal matings between the dozen or so best clones as recommended by E.H. Wilson for Boston. I have never published the results because the work was done in a commercial nursery on Long Island, where many of the labels became mixed and the populations that were identifiable were mostly too small for statistical significance after the nursery workers had scrambled them up. Throughout, however, it was evident that most of the parental material was highly heterozygous. For your information, I will say that most of the progeny was either of the purple color or of intermediate type, but with no significant dominance of one color. For practical purposes, however, there were a few interesting evidences of inheritance. I found that red x red (such as 'Atrosanguineum' x 'Charles Dickens') gave progeny having a much higher percentage of reds than could be otherwise obtained. I also found that the character of ruffled edges on the flowers (as in the clone 'Everestianum') appeared to be transmitted to F1 progeny. I also found in deciduous azaleas (R. calendulaceum and probably R. mollis) two yellow-flowered plants crossed together produced only pure yellow offspring. So far as hardiness went, I found that hardy x half-hardy species produced seedlings that were intermediate in their hardiness. But I also found that the usual standards of hardiness, as measured by British and American ratings, often did not apply, so that one might hope to get some truly hardy offspring from certain unexpected combinations. I am banking on this for some of my present work, although I expect to find it necessary to keep on crossing and back-crossing for some generations in many instances. But the thing that has interested me is that I have seedlings between hardy American and tender oriental parents that presently seem to be standing the gaff of Long Island outdoors. They haven't bloomed yet, so we can't tell too much; one must always remember that induced apogamy apparently exists in the genus. I suspect apomixis in some plants of R. catawbiense. I also have made azaleodendron crosses (R. catawbiense x R. calendulaceum) obtaining seedlings of intermediate foliage character, but which were weak and do not survive to bloom. Azaleodendrons are sterile.
        Recently I have used R. maximum extensively to avoid the lilac color and for hardiness. It has the disadvantage of being slow, but its hybrids in the past have been better than the wild parent. I have also used some of my previous late-blooming hybrids (containing maximum genes) in crosses with exotic species and hybrids obtaining pollen imported from Britain and from the West Coast. The anthers can be cut off bodily and shipped by airmail, then placed in capsules or in desiccators in the presence of calcium chloride. In 1927 I tried 16 different sets of temperature and moisture conditions for pollen storage, and found complete dryness at room temperature worked the best. I reported this at the 1932 genetical congress.
        The old records indicate that much of our best color in the Catawba hybrids has come from R. arboreum and other tender species, through several generations of subsequent inter-crossing of the progeny. Whether this is the shortest way to proceed or not, I am trying everything at first, and so have done a somewhat systematic job of crossing hardy American material with highly colored half-hardy or tender species and clones from abroad. Not anything of significance has bloomed yet, since these were all made within the last four or five years. If we get some good F1 material, which will probably not be hardy itself we may be able to do something with its F2 or later. For safety against winter-killing of valuable F1 plants, I am having most of them grown at the Farmingdale Station on Long Island and a few at University of Washington Arboretum in Seattle, both places being much milder than Ithaca. We carry a few under glass at Cornell, but besides the cold, we also have "hard" alkaline water there and can water our plants only with distilled H2O or with rain. This makes matters slow and difficult.
        As briefly as possible, let me add a few more practical points: Crosses between lepidote and elepidote sections of the genus seldom work. R. carolinianum2 (lepidote) is hard to cross outside its series, except with the Alpine Rose3, R. mucronulatum and a few others. I have tried to put yellow on it unsuccessfully. Practically all species, including great numbers of the Chinese sorts, seem to be genetically unstable in nature and vary widely from the type. They appear to be heterozygous in color pattern and other features, and without long and expensive genetical research one cannot predict what their basic genes really are like. In the ones we work with, there seems to be no polyploidy, except in R. calendulaceum, which is a tetraploid. The basic chromosome number is 13 and not 12 as I reported. The most complete study of polyploidy has been made by Dr. Janaki of the R.H.S. and is as follows: Ammal, E.K. Janaki. "Polyploidy in the Genus Rhododendron". Royal Hort. Society Rhododendron Yearbook, 1950; p.92-98.
        Almost complete self-incompatibility existed in about 25% of the species and hybrids I tested in the late 1920s, mostly American materials. Only about 25% of the others seemed fully self-fertile, the 50% in-between exhibiting various degrees of self-incompatibility ranging from very feeble to fairly normal seedlings from self flowers. A huge number of them were so depleted in vigor that they barely existed and slowly perished before coming to blooming size. I suppose I should have done more work with those which could be carried to bloom in an effort to isolate genes and recombine them later, but that is just one of the many things that circumstances have not permitted me to do, and which I may tackle later. It is difficult to carry along weak individuals, which is what you have to do in most cases of self-pollinated material.
        At Cornell, we have worked out a new system for raising seedlings (not yet published) and have also grown them on sugar-agar media exactly as orchids are grown, in cases where we had only a very few rare seeds. Look out for hard water and keep the soil reaction around pH 5.0. Malnutrition effects sometimes simulate fungus infections in appearance. We have found that Knudson's Orchid Solution "C" is a good nutrient for rhododendron seedlings growing on pure granulated peat moss.
        I have not worked recently on azaleas, but feel that these are better than the evergreen sorts to grow in cold climates. If I were you I would raise a lot of seedlings of the American species, which exhibit great variation, especially R. calendulaceum and its forms. The American species are longer-enduring than the mollis kinds. I think you will find it very rewarding to try them out and also get seed of the best Exbury, Goldsworth (Slocock) and improved Knap hill hybrid Ghent Azaleas from England. I do not think the English selections will prove to be so good over here as to get a lot of mixed seed of the best kinds and make your own selections after trails.
        I shall enclose a mimeographed copy of a list of cold-weather rhododendrons and azaleas as selected for this region. It is quite old and rather incomplete.
        Please get in touch with me again if I can help some more. And please remember me to Dr. Senn if he is there; I served on a committee with him in London last year at the Horticultural Congress.

Very sincerely,

Clement Gray Bowers
Research associate, Cornell University
and Professor of Botany,
Harper College, State Univ. of New York,
Oct 2, 1953

1 Now subsection Fortunea.
2 Now R. minus var. minus Carolinianum Group.
3 Probably is referring to R. ferrugineum and R. hirsutum of the European Alps.

Comments by John Weagle
(Specific comments to the text are in italics.)
        A few observations on Bower's letter seem in order. My first thought was what little contact there was between North Americans and Scandinavian test sites like the Göteborg Botanic Gardens. The important information that these worlds could have gleaned from one another was substantial. The potentially useful R. purdomii, R. rufum, R. nigroglandulosum, R. phaeochrysum and R. przewalskii were being grown at Göteborg which, while hardy enough, may not have tolerated the heat in a large portion of eastern North America including Ottawa. Good-looking tough species like R. bureavii and R. bureavioides, similarly heat sensitive, had most likely not been tested in colder areas at that point. Peter Tigerstedt Sr.'s knowledge and introductions in Finland in those early days could have helped the easterner pioneers immeasurably. Tigerstedt at this point already had his super-hardy R. brachycarpum which had endured more than twice the bottom limit of -20°F (-29°C) that Bowers noted for evergreen rhododendrons in North America. Furthermore this R. brachycarpum (now within the Tigerstedtii Group) and the dwarf R. brachycarpum Roseum Group as well, have little trouble transmitting colours compared with R. catawbiense, R. maximum and their hybrids. These species could have contributed (and could still!) their hardiness in the F1 and F2 generations and added needed variety into so many North American hybrids which suffer a certain sameness about them. Members should realize that R. degronianum ssp. yakushimanum was not freely available in North America until the mid-1960s. My comments in italics follow statements quoted from the Bowers letter.
        "Only one of the Obtusum azaleas will grow here (R. poukhanense), and R. kaempferi will usually kill to the ground with prolonged temperatures of -15°F (-26°C)." Hybridizers seem to have made much headway pushing the boundary for the evergreen azaleas northward since those early days. Various forms of R. poukhanense and R. kaempferi and the Gable crosses using these two crossed together have been valuable in this pursuit. I have to wonder if the rock-hardy species R. kiusianum was at their disposal. It has proved to be a very tough species and is only now being combined with more tender varieties to produce a line of potentially hardier evergreen azaleas. It would be of interest to see if winters have gotten milder in Bowers' test area since those early days.
        "I would suspect that the Dexter hybrids and others of the Fortunei Series, which are about the hardiest of the newer sorts, would be extremely unreliable at -15°F (-26°C) and could be depended upon where boxwood might survive with slight protection." These assumptions about the hardiness of the Dexter hybrids were well ahead of the times and accurate for the most part.
        "Claims made for survival under sub-zero temperatures are not valid if they involve only survival under one extraordinary night. You will find many such claims in the current literature."I was particularly pleased to read this statement. These "sub-zero" claims still abound today in both literature and nursery catalogues especially those originating on the West Coast. I still maintain that those in mild climes do not have the foggiest notion of what constitutes a bad winter. Cold temperatures are but one of the worries facing a rhododendron in these northern climes. Just try growing a big Glenn Dale azalea developed in Washington, D.C., in milder but cooler-summered Edinburgh or Halifax! Bowers' caveat is a most important lesson a breeder will heed - one will NEVER go wrong breeding too much hardiness into a plant. Imagine basing your life's work on a plant that proves tender halfway through the arduous breeding process. I believe a good twenty years of testing is required to prove a plant's hardiness in our climate, and yet breeders everywhere churn out new material purported to be fully hardy after but a few years in the field.
        It is no surprise that Bowers had knowledge of the important true white selections of R. catawbiense in the hands of Gable, Glass and Harmon; how many years would have been saved if the pioneers had started their breeding with the advantage of those plants? I would concur with his findings with 'Everestianum' - my only cross of 'Everestianum' x 'Olin O. Dobbs' produced an entire lot of ruffle-edged progeny. His note that hardy species x half-hardy species produced seedlings intermediate in hardiness is a rule I am hoping is steadfast in my own programme using the super-hardy R. brachycarpum as mother and big-leaf species like R. rex as pollen parents, in the hope of opening the doors to hardy big-leaf look-alikes for coastal Nova Scotia. To do the same for Ottawa might very well be impossible, but such a pursuit would certainly require the hardiest possible R. rex - be it highest altitude or most northerly rather than simply the best form. Even that approach may not give sufficient Ottawa hardiness.
"In 1927 I tried sixteen different sets of temperature and moisture conditions for pollen storage and found complete dryness at room temperature worked the best." This rather baffles me; modern day reliable freezers were certainly not available then, but refrigerators certainly were. These tests would be worth reviewing. "R. carolinianum (lepidote) is hard to cross outside its series, except with the Alpine Rose (R. ferrugineum)." This cross was unknown to me and aroused my curiosity. Is this 'Myrtifolium'? It is unfortunate he did not have the luxury of yellow R. keiskei 'Yaku Fairy' and Kehr's tetraploid 'Epoch'.

Comments by Peter Tigerstedt
It has been clear to me that one of the major reasons for lack of hardiness in breeding material of rhododendrons has been the fact that plant explorers (Wilson, Kingdon-Ward, Forrest, Rock and others) some 100 years ago and earlier mainly collected in areas in China and elsewhere where the climates were more or less like in the UK, France and generally Central Europe. Therefore they frequently missed the most harsh locations (high altitudes or northernmost). Often the same appears to have happened in the Appalachians. Also there was not enough understanding in those days for ecological gradients (clines) or for ecotypes. The notion of ecotype, which means a locally adapted and genetically distinct subgroup within a species, was first launched by Turesson in Sweden in 1922 and continued by Clausen, Keck and Hisey some twenty years later in the US. The notion of cline, which means a gradual change in genetic adaptation of a species along ecological gradients, was coined by Huxley in the UK about 1940. When it comes to plant hardiness one has to consider at least three major clines: 1) a maritimity-continentality cline and 2) a south-north cline and 3) a low-high altitude cline. I have the suspicion that the early explorers mainly saw the species as a unit and did not consider the most important within-species genetic variation in adaptation to climatic conditions. What was collected in those days must clearly have influenced the results in rhododendron breeding in the 1950s when the three articles were written.
        Another fact that was often overlooked by the breeders was the "within seed lot" (within-population) variation in hardiness. We have seen that, repeatedly both in rhododendrons and several forest tree species, there may be considerable genetic variation in hardiness between individuals of a seed lot. Thus at the time of introduction, a few plants do not tell you the truth; you ought to work with populations of hundreds to single out the hardy ones. The same of course concerns F2 hybrids where character recombinations may cause very large differences in hardiness even between full-sibs having the same parents. Again one should work with hundreds of plants in the family (siblings).
        Some specific comments to the Bowers text (comments in italics):
        "There isn't much available genetical information on rhododendrons that will help with breeding for hardiness...I have as yet very little F2 material to base any conclusion upon." This was the case at that time. Bowers seems to suspect F2 variation in hardiness, but he has no evidence.
        "In these first crosses I made (1926-29) systematic checkerboard reciprocal matings between the dozen or so best clones as recommended by E.H. Wilson for Boston...the populations that were identifiable were mostly too small (probably just a few plants) for statistical significance." Again he crossed between best clones for Boston and evaluated only a few plants per cross.
        "I found that hardy x half-hardy (he clearly classifies a species as hardy or semi-hardy without noting within-species variation in hardiness) produced seedlings that were intermediate in their hardiness." I agree with the intermediate, hut hardiness may depend on how the cross reacts along a continentality-maritimity cline and a south-north cline and a low - high altitude cline. We have, for example, found in crossing Japanese (maritime) and Siberian (continental) larch, that you can change the growth profile of the hybrid, thus tailoring it to, for example, a semi-maritime climate like ours in Finland.
        "I have not worked recently on azaleas, but feel that these are better than evergreen sorts to grow in cold climates." If you look at the "Northern Lights" series developed by Harold Pellett for Minnesota and other continental states, this comment is very true. I think it partly is due to late-winter desiccation of evergreen rhododendrons in those regions where sunshine in late winter can he intensive on the leaves, but the plant can not take up water due to frozen ground - this is another kind of plant hardiness!
        The comment on "one extraordinary night" needs a note. Testing for hardiness by freezing in a cooler can never tell you the truth that you get by testing in a specific climate. Freezing under one extraordinary night can only specify particular bud or shoot hardiness at a certain point in time, but certainly does not tell you the plant hardiness through the whole winter We have found that generally plants that originate from extremely cold continental climates will flush early and get damaged by spring frosts in Finland. Again plants that come from cold maritime extremes will grow too far into the autumn and will he damaged by frosts at that time. For us the only right thing is to cross between those two growth profiles and thus tailor the plants for hardiness in our climate.

Volume 60, Number 1
Winter 2006

DLA Ejournal Home | JARS Home | Table of Contents for this issue | Search JARS and other ejournals