Sex And The Single Rhododendron
David Leach, Brookville, Pa.
Dr. Leach presented this as an informal talk, illustrated, whenever a plant was mentioned, by a slide of that particular plant. This made for a most informative presentation. Obviously it is somewhat difficult, without the illustrations to report it for the Bulletin. The speaker was kind enough to permit me to use the notes from which he spoke and I hope I have the important points of fact, although lacking the color of picture and voice. - Ed.
I seem to be a perennial fixture at A. R. S. affairs and if you're getting tired of looking at me, I'm having a problem trying to find new things to talk about. I've spoken at meetings of all the Chapters in the East, I think, and for some of them two or three times. So I find myself sympathizing with the remark of Barbara Hutton's seventh husband on the eve of their honeymoon. "I know what to do", he said, "but I'm not so sure how to make it interesting."
I see that the title of my talk is listed in the program as "Sex and the Single Rhododendron." A word of explanation about that!
Many of us here know that there has been an unfortunate custom of giving a group name to all of the seedlings resulting from a cross. Formerly, for example, all of the progeny from griersonianum crossed with dichroanthum, were entitled to be called 'Fabia'. Now the technical word for a group name is grex, but most of us think that only clone names should be used for each single rhododendron.
So when Dr. Ernie Yelton called me several months ago to ask me to appear on this program today, I proposed to talk about grex and the clone. But to show you how his Freudian mind works this came out in the printed program as "Sex and the Single Rhododendron".
I've been instructed to talk about breeding rhododendrons this afternoon and people are always asking me about the flower color gene chart in the back of my book and how I arrived at the conclusion. The red and pink hybrids now in commerce in the N. E. U. S. are badly flawed by blue. There are just no clear colors among them. We have no hardy yellow or orange flowered rhododendrons at all. So one of the important things in attempting to produce improved hybrids for cold climates is certainly flower color. In trying to deduce the manner in which flower color is inherited, I got the first clue from this extraordinary result:
The tender Asiatic rhododendron called scyphocalyx was crossed with a red rhododendron called kyawi, after a Burmese collector. As you might expect, it produced for Mr. de Rothschild an orange-red hybrid which he called 'Indiana', much too tender, of course for the Northeast. Well, I crossed the orange-red 'Indiana' with catawbiense var. album, and to my great surprise I got from this cross a yellow flowered, semi-hardy hybrid. It is worthless as an ornamental, but why were yellow flowers produced from a cross of an orange-red with a white?
The next surprise came the following year. I had crossed our native northern maximum with a red flowered rhododendron, a familiar commercial hybrid on the West Coast called 'Jean Marie de Montague'. From this cross I got a hybrid, ordinary in every way except that the flowers were red. Now why weren't the flowers pink? I had made scores of crosses between red and white flowered rhododendrons and the progeny were always pink flowered. I understand that this is not so uncommon in breeding tender rhododendrons in the British Isles, but it was my first experience.
Putting together these two extraordinary results, and adding to them the observations made from hundreds of other crosses, I concluded, then, that rhododendron flower color was probably inherited in the manner shown in this chart (shown on slide). A horizontal line represents dominance; a vertical line represents recessiveness. Epistasis, or the suppression of one group of genes by another is shown by a parallel line ⅛" immediately below the main indicator line. To find the gene status of any given color, start at that color in the right column and follow the line leftward and upward until all six genes are represented. Dr. Bowers and Dr. John Yeates in New Zealand have both informed me that on the basis of their experience they can find no fault with the conclusions. On the other hand, Dr. Mehlquist seems not to agree.
There is no particular problem in increasing flower size in breeding rhododendrons. Here's (slide) an example of it, a cross of 'America' with 'Pink Pearl'. But the blue admixture which so often flaws the color purity is another matter. It is extremely difficult to eliminate, and so this hybrid was destroyed. We know the reason, of course, from the chart we saw a moment ago. There are two different genes, B. and P. producing in the purple, magenta or violet range. If either one, or both, of them are present as either homozygous or heterozygous dominants, blue is produced to flaw the color. This makes a very tough breeding problem.
Stature is an important consideration in breeding rhododendrons. People are no longer building 2 and 3 story houses. The need is for dwarf and semi-dwarf hybrids of appropriate scale for single story houses and small gardens. Here's (slide) what you'll eventually get if you go down to your friendly neighborhood nursery and buy some rhododendrons. The house is being strangled by rhododendrons, almost like a Charles Addams cartoon. What we need are semi-dwarf hybrids that will stay in scale.
Well, we have four species that seem to contribute dwarfness very satisfactorily. The first of these is williamsianum, from 9,000 feet elevation in Szechuan province in China. I mated it with an early hybrid of Joe Gable's, catawbiense crossed with discolor, which is very vigorous in growth and will probably be at least 15' eventually. It was like crossing a mouse with an elephant, or a parrot with a tiger. The latter, incidentally, is alleged to have succeeded and when the breeder was asked what he got he replied, "Not much, but when it talks, I sure listen." In any case from this mating of williamsianum with the very vigorous Gable hybrid, I got the plant stature you now see on the screen. After 12 years the plants are 15" tall. There's just one hitch. They still haven't set flower buds. And a second hitch is that the growth is too slow to he of interest to the commercial nurserymen. In general, first generation williamsianum hybrids languish in our hot, arid summers, and I have not been particularly pleased with this species as a direct parent. I much prefer to use williamsianum hybrids as parents and here (slide) are a couple of examples of the results. The white Catawba rhododendron crossed with 'Adriaan Koster' by williamsianum and catawbiense var. album by fortunei crossed with 'Eidam' by williamsianum. These retain the fine dense growth habit of williamsianum, are free-flowering and semi-dwarf in stature.
Another valuable parent for dwarfness is R. chrysanthum. As you can see from this slide this plant is about 8" tall, and this gives you a better idea of the stature of quite an old plant of chrysanthum. Incidentally, I do not find this species at all hard to grow. It flowers from seed in about six to seven years, and presents no problems at Brookville, despite its reputation of being difficult. In any case, chrysanthum crossed with 'Belle Heller', a very vigorous hybrid from Tony Shammarello, produced progeny which at six years, are 8" tall and now starting to flower freely. Again, I suspect that these may be just a little too slow to be of interest to the commercial nurserymen. But I believe these chrysanthum hybrids will be very valuable parents for further breeding.
Another species which contributes dwarfness is forrestii, a tender alpine from Tibet, Yunnan province of China, and Burma at about 13,000 feet. Unfortunately the first generation forrestii hybrids are hopelessly tender for the Northeast, but crossed with such red flowered British hybrids as 'Jean Marie de Montague', the progeny can be grown as practical garden plants in mild climates. Now when these first generation forrestii hybrids of intermediate hardiness are crossed once again, this time with extremely hardy parents such as 'America', the results are very gratifying to see. The plants are hardy, dwarf but not too dwarf, densely foliated and practically all of the blue has vanished from the flower color.
I suppose R. yakushimanum is being used more by hybridizers than any other species. It has almost every virtue and almost no faults. It is not quite ironclad hardy, however, and the professional nurserymen say it grows too slowly to be profitable. For those two reasons, I crossed it with the white form of the Catawba rhododendron, and got a uniform batch of hybrids of exceptionally high quality. This (Slide) is one selection called 'Spring Frolic', scheduled for introduction in 1969. 'Spring Frolic' has ornamental new growths, as you can see here. The indumentum, however, is thin. Otherwise, I believe it captures all of the charms of yakushimanum, while being ironclad hardy and satisfactorily vigorous for professional nurserymen.
Of course hardiness is the biggest problem of all in breeding rhododendrons for the N. E. United States. Hardiness certainly seems to be quantitative in its inheritance in rhododendrons. You usually get the classic additive effect. The more hardiness genes there are in the ancestry, the hardier the progeny will be, figuratively speaking.
R. hanceanum var. nanum is a nice dwarf scaly leaved rhododendron. I crossed it with carolinianum, by far the best parent to impart hardiness in scaly leaved crosses and this (slide) is a more or less typical result in breeding scaly leaved rhododendrons. The genotypes of the most desirable tender scaly leafed rhododendrons are so dissimilar from the gene complement of carolinianum that apparently they fail to work reciprocally, and extreme lack of vigor often results. R. carolinianum, as a seed parent also characteristically produces many somatic apomicts. This is such a problem, these apomicts, that I no longer use carolinianum as a seed parent. It is used solely as a pollen parent, and tender seed parents are grown in pots with protection over winter. In many crosses with carolinianum used as a seed parent, 100% of the progeny will be apomicts, that is, reproducing carolinianum only, without hybridity.
On a preliminary basis, R. ludlowii appears to be very promising as a parent, for the introduction of yellow color into hardy, scaly leaved hybrids, along with dwarfness. As you see in the picture (slide) a 4" label is holding up the flower. The hybrids derived from this species bloom when they're three years old. I'm sorry I don't have a picture of them to show you, but they're pale yellow.
Just to give you an idea how important this business of selecting good parents is, here (slide) is the typical magenta-pink R. catawbiense, which Mr. Lem crossed with 'Fabia' and a quite ordinary pink hybrid resulted. But Mr. Lem also crossed catawbiense var. album with 'Fabia' and he got a quite distinguished hybrid, which I would think would be worth trial at least as far north as New York City. R. catawbiense produced nothing of interest but catawbiense var. album sired a winner.
Here you see on one side of the slide the familiar hybrid 'Lady Armstrong', attractive enough but with flowers and a truss only about a third of the size of the finest tender hybrids to be found in the United Kingdom and on our west coast. I crossed 'Lady Armstrong' with the large flowered tender 'Pink Pearl' and got the poisonously colored, half-hardy hybrid with bigger blossoms that you see on the right. And herein lies the story. Suppose we liken our hardy parent to a flock of black sheep. It's familiar, we're tired of it, it's not really very good, and all we can say for it is that it survives our winters. Imagine then that each sheep in the flock represents a gene, one of the minute bodies in the cell nucleus which determines all of the characteristics of a plant's offspring. Along comes one of those spectacular, giant flowered, tender rhododendrons and we decide that it is a good bet to cross the two. The dazzler has all white genes, we bring the two together. We make the cross, with a vision of the splendid white sheep separating out in a flock with a couple of black sheep tagging along to provide the hardiness we want. But that isn't the way it works. We forget that each flock is contributing the same number of sheep to the pool. For every hardiness gene, there is a gene for non-hardiness. For every gene for yellow flower color there is a gene for non-yellow. For every gene for dwarfness, there is a gene for non-dwarfness. In any case, our first generation is usually midway between the two parents in almost all respects. In a cross between a hardy and a tender rhododendron, the first generation will be half-hardy. In a cross between a red and a white rhododendron, the first generation will usually be pink. The same goes for most other characteristics, because the one parent is contributing as many genes as the other. So we have a flock with the sheep half black and half white. (Illustrated by slides).
But if you take two of these flocks and intermingle them once more the results are quite different. The same thing is true if you cross two of the first generation hybrids. In the next generation the sheep have had some lambs, figuratively speaking, and the flock has white and black and gray sheep in it. These represent the genes in one type of hybrid we'll get in the second generation. The black sheep have given us hardiness but the gray sheep won't give us the full ornamental quality we want. Another type of hybrid in the second generation doesn't have nearly enough white sheep in it. It will be of lower quality still. But a minor portion of the second generation will have mostly white sheep with just enough blacks to give us what we want: all of the good qualities of the original white flock with the hardiness of the black. You can not get this result by mingling an equal number of black sheep and white sheep in the first generation. You must take two mixed flocks and mingle them once again. So don't expect too much from your first generation rhododendron hybrids. Don't be discouraged. So don't throw away your first generation because the hybrids are nondescript: half-hardy, or half-red or half-dwarf. Regardless of how poor they may appear to be, cross the two best first generation hybrids once again and the chances are good that in the second generation your shining vision will become a reality.
Well, you say, show me. Here (slide) we have the familiar hybrid, 'Mars', which Frank Knight will probably recognize as having been photographed at Wisley. It's not hardy at Brookville. I crossed it with catawbiense var. rubrum and made a selection from among the progeny which I called 'Blaze'. It's quite an improvement over our standard commercial hybrid 'Nova Zembla', as you can see from the single flower of 'Nova Zembla' pushed into the side of the 'Blaze' truss. It's also very vigorous in growth and has exceptionally good foliage. But it still wasn't the brilliant color I had in mind. So I back-crossed this hybrid onto 'Mars' and this (slide) is the result which showed up in the second generation. It has the brilliance and purity of color I was seeking. But I didn't get it in the first generation; it appeared in the second.
As another example, take 'Mrs. Furnival', which has a very bold blotch. It too is tender at Brookville, but I wanted something on that order which would be hardy to 20° below zero. So I crossed 'Mrs. Furnival' with the white form of the Catawba rhododendron, and got quite a nice batch of hybrids, of which this (slide) is one selection, to be introduced. But I still hadn't achieved my original goal. So I crossed these two first generation descendants of 'Mrs. Furnival' together, and in the second generation I got the bold blotch I was seeking, a much larger truss, and the good foliage of 'Mrs. Furnival'. But it took two generations to achieve the goal.
Most of us know 'Pioneer', a hybrid of racemosum and mucronulatum made by Joe Gable. It has been extremely popular, but some people have thought the pink color a bit too bluish, and it has not been bud hardy in recent years in my extremely cold climate at Brookville. So I self-pollinated 'Pioneer' and got, in the second generation, this (slide) clearer, brighter pink which is even more bud hardy than mucronulatum, its grandparent. But it took a second generation to obtain the result. I'd like to add here that wherever possible, I would recommend sibling crosses to obtain the second generation for which I am plugging so hard. The results are almost always better than self-pollination of one of the first generation plants. In the case of 'Pioneer', I had no choice. But ordinarily it is much wiser to cross two different plants of the first generation to obtain the second generation, in rhododendrons at least.
Now what about orange color in hybrids hardy enough to be grown in the Northeast? Here is a tender hybrid, 'Fabia' by discolor, produced by Lord Swaythling. I crossed it with catawbiense var. album and it produced this (slide) hybrid, which is about as close to orange as I've been able to get, so far. The second generation has not yet flowered.
And to show you that the external appearance of a rhododendron does not give a very good indication of its value as a parent, here is 'King of Shrubs', in a picture which Dr. Phetteplace was kind enough to take for me. It is somewhat similar to the Swaythling hybrid but has deeper, richer coloring. But crossed with catawbiense var. album, it produced only a disappointing ivory color. It sometimes seems that you can't win. It's like the fellow who quit smoking because he was afraid of lung cancer; he took to chewing toothpicks and died of Dutch Elm Disease. But the second generation from this cross may tell a different story.
Occasionally, of course, you do get satisfactory progress in the first generation. Lionel de Rothschild crossed dichroanthum, here seen on the screen, with the mammoth flowered tender griffithianum. He then took one of that hybrid and crossed it with auriculatum. The result was, of course, much too tender to be grown at Brookville but Peter Barber sent me pollen from it and I crossed it with our old friend, the white form of the Catawba Rhododendron. I found among the progeny this (slide) hybrid which I called 'Duet'. This one will be introduced in a couple of years. This was an exceptionally lucky cross because a sister seedling which I called 'Peach Parfait' seemed worth naming too. And still another one from the same cross has been put aside for further observation, as well as a fourth. There is quite a variation in these four sister seedlings, all from the same cross.
A wild hybrid from LaBar's Rhododendron Nursery has been a good parent for me. I assume it to be the result of a traveling salesman bee, flitting from high altitude catawbiense to a low altitude maximum. In any case, crossed with a 'Goldsworth Orange', it produced an interesting hybrid which I rather like. Lionel de Rothschild crossed dichroanthum with Rhododendron discolor. The resulting hybrid was then crossed with campylocarpum and the best of the progeny was called 'Jasper'. It attracted me for the richness of its coloring, so I obtained pollen and used it on the wild hybrid 'Russell Harmon'. The cross produced 'Tahiti', which is scheduled for introduction in 1969 and 'Serenata', which is quite a distinctive rhododendron to be hardy at 20° below zero.
Here (slide) we have the famous Rothschild hybrid, 'Crest', probably the supreme achievement of the renowned British breeder. But crossed with the white form of the Catawba Rhododendron, the first generation hybrids, one of which you see on the screen, have been rather disappointing. We shall have to wait for the second generation.
My best parent for producing yellow was another Rothschild hybrid, made by crossing fortunei, with wardii. I used pollen from that hybrid on, once again, the white form of the Catawba rhododendron, and found among the progeny a seedling I named 'Limelight', which is scheduled for introduction in 1969.
'Goldfort', a British hybrid from Slocock's Nursery, is not really very Gold, but it is hardier than most British yellows, so I crossed it with the white Catawba and got this rather pleasing ivory, which most visitors seem to like. This, in turn, was crossed with the yellowest of the progeny resulting from the mating we saw earlier of catawbiense album x (dichroanthum x griffithianum) x auriculatum and the result was a great disappointment. Even though this was the second generation, and I might have hoped for a much stronger yellow, I evidently did not grow enough seedlings to obtain the segregation of the yellow genes in the right fashion to produce the pigment saturation I wanted. Reminds me of the story of the man who said his wife was a great help in decision-making; she was always wrong.
A direct cross of catawbiense var. album with Rhododendron wardii from the Sheriff expedition yielded a fairly good yellow which has been numbered and set aside for further observation. But I am beginning to think that for real honest-to-goodness, deep dandelion yellow, we are going to have to use the type of cross in which dichroanthum appears in the parentage of one hybrid and wardii or campylocarpum appears in the parentage of the other. Here (slide) is an example, a hybrid made on the West Coast by Carl Sifferman, a cross between a dichroanthum and a wardii hybrid. It is, by far the deepest yellow rhododendron I have ever seen.
Since I was instructed to talk about breeding, I am going to show you quickly now a few hybrids which must necessarily be of my own making for me to know very much about them. 'Swansdown' is going to be introduced in a year or two. It resulted from a cross of catawbiense var. album with 'Belle Heller'. By coincidence, Tony Shammarello made exactly the same cross and called his best seedling 'Ice Cube'. 'Boule de Rose' is a pink edition of 'Boule de Neige'. It grows up to about three feet and then spreads outward. At the present time the plant is 3' high and 9' across. Unfortunately, it has been a lousy parent. I would like to retain that habit of growth in hybrids with flowers of other colors.
R. catawbiense album 'Glass' crossed with a Dexter hybrid by Edmond Amateis produced this (slide) fine Rhododendron from one of the plants in a flat of small seedlings that he gave to me years ago. I intend to name it for him. I crossed 'America' with a Dexter hybrid that I got from his original place at Sandwich, Mass. and got this rather unusual rhododendron. (slide). 'Vernus' is scheduled to be introduced next year by the five nurseries which propagate and sell my hybrids. It owes its early bloom to Rhododendron caucasicum, and the landscape architects like it because it blooms right with the daffodils and dogwoods. There has been a need for a completely hardy Rhododendron to do that for a long time. This one flowered after 35 below zero in 1963.
'Betty Breene' came from a cross between smirnowii and a Dexter hybrid. Visitors, particularly women visitors, seem to like it very much, but I've withdrawn it because propagated plants won't set buds until their fourth year.
'Janet Blair' has already been introduced. It was named for the entertainer who came from Blair County, not far from my home in Pennsylvania. The previous picture was Kodachrome. This close-up will show the very large, ruffled flowers of a sort of nightgown pink. This shot was made with Ektachrome and the truth lies about half way between. Anyway, 'Janet Blair' is the sort of constant reminder that keeps rhododendron breeders from getting too cocky. The cross was made by a bee; it's a waif with an unknown father, and the wayward mother probably produced a better child than if I'd officiated at a formal marriage.
Now in closing, just a few slides of unusual rhododendrons or unusual uses of them, which I thought you might enjoy seeing. A rare, red tipped form of Rhododendron keiskei. A very unusual, red striped form of Rhododendron fauriei found on Mt. Asama in Japan.
The Japanese like to grow the dwarf form of Rhododendron dauricum in containers. I have a few plants of this dwarf form but it seems not to be generally available commercially, so I propose to send seeds to the Society's seed exchange to get it distributed.
People who walk through my garden when this (slide) is in bloom almost always stop and ask what kind of Spirea it is. Actually it's Rhododendron micranthum, a scaly leaved species that is hardy almost anywhere. I've tried many times to make crosses on it. Seeds are produced but they have never germinated.
An unusual use for rhododendrons, 'English Roseum' used as a hedge in a garden designed by Orlando Pride of Butler, Pennsylvania. Certainly it seems much more interesting and colorful than the usual array of hedging plants we see.
And the deciduous Azalea 'Red King', with Clematis candida languinosa planted to climb up through it. It's an arresting feature in Tony Shammarello's display garden.
Most of us think of something like this when someone mentions the West Coast native Azalea, Rhododendron occidentale. But this is an extremely variable species and I'll show you just three out of 20 or 25 quite striking variants that can be found in Northern California. Here's one with semi-double flowers and the color pattern on this one seems to me quite striking. This one looks more like a Magnolia with two flowers hose-in-hose. If I were breeding azaleas on any scale, I would certainly make use of the variability to be found in Rhododendron occidentale. It should be possible to create a whole new race of distinctive hybrids, using these extraordinary forms of the western Azalea.
In conclusion now, I'd like to show you a dozen slides of the New Guinea rhododendrons and how they grow in nature. These rhododendrons are virtually unknown. Many of them grow like orchids, high in the green roof of the tropical jungle, forced through millions of years to an aerial life in order to receive enough light to survive the jungle competition. Here we have zoelleri with flowers 1 to 5". It makes a shrub about 8' high. Still another color form of the same species, this one from Telefomin in Papua. The rainfall here is 150"; in contrast, you have about 38" here in Asheville. As you can see, this is quite a striking and colorful species.
Here we have a terrestrial species of unusual appearance, growing at an altitude of about 1500 ft. in the New Guinea mountains. Not all of the New Guinea rhododendrons are outstanding ornamentals, by any means. When they are terrestrial, they're quite likely to grow out in open fields as you see here. But many of them are extra ordinarily beautiful. It hardly seems possible, but of about 200 species growing in New Guinea a large number have been discovered within the last five years by Dr. Sleumer and by the Archbold Expedition. Here we have one called konori. Unfortunately, the climate of San Francisco is about as severe as these rhododendrons can endure outdoors. Jock Brydon has 25 or 30 different species growing at the Strybing Arboretum.
One of the most common of the New Guinea rhododendrons is macgregoriae, and here we see it as an epiphyte, growing in nature. The foliage of macgregoriae is said to be extremely poisonous to livestock. There are about 12 to 15 flowers, each 1½" across making up the truss of this species.