Compiled and edited by Ian Donovan, Pembroke, MA
In the 1970s and 1980s on the West and East Coasts, those ARS members who were interested in breeding rhododendrons and azaleas met to formalize their information exchanges, recording and publishing the resulting sessions verbatim. The sheer amount of effort involved in transcribing and editing these recorded sessions contributed to the demise of published reports after 1988. Our thanks to the many volunteers who persevered and preserved these personal records. You have made this project possible.
With this issue of The Rosebay we begin extracting from those reports the remarks of the late Dr. Gustav A. L. Mehlquist. He was a pioneer researcher and a teacher to many of us as we grappled with how to be more effective in our pollen dabbling. His sense of humor, his scientific approach to breeding, and his need to explain to us the fundamentals of botany and applied plant genetics come through in each of his talks. We start this series with his remarks before the East Coast Rhododendron Hybridizers Symposium, hosted by the ARS New York Chapter at Planting Fields Arboretum, March 1, 1975. Only minor corrections in spelling; adjustments in punctuation and paragraphing; removal of some vocal pauses; and identification of people, plants, and references the first time appearing have been made to improve readability and understanding. Ian Donovan
Thank you, Dick [Richard Murcott, Symposium Moderator].
This has been a very interesting session so far. Being a plant breeder, I'm accustomed to being put in various groups, but this is the first time I've been placed in the general group of blooming idiots. I trust I have a good many friends with me.
I also learned that Linc Foster [H. Lincoln Foster] is frightened by me and I'm delighted. Every time I get up to his place he starts showing me plant after plant. "Well, you know this one of course and this one of course and this comes from such and such an area and this is a hybrid between the two." Of course, I know them, I don't have the guts to say I've never seen them before!
The same thing happens every time I go visit somebody who has some experience with plants. They nearly always work with something that I'm not familiar with. That, after all, is very good because in the few years that the average man can devote to any project he cannot cover a very large segment of the rhodo field. The opportunities are tremendous. My own work has been largely with the large leaf rhodos, which I won't go into much because that would enlarge the topic too much.
I would like to concentrate on extending a few ideas that Dr. [August E.] Kehr developed [earlier in this symposium]. I didn't know what Dr. Kehr was going to say and he didn't know what I was going to say, because he didn't even know I was on the program. As he said, he could not do justice to the whole field and there are a few things that I think would be worth commenting on. At least I find them usually in my own work.
My own work, aside from the hybridization of large leaf species, has been with very few azaleas and very few of the so-called dwarf species. Having a garden that is much too small for the number of plants I want to grow, and I know that many of you have similar problems, I've been interested in producing small, compact hybrids, if that's possible. It has, of course, another advantage that has already been pointed out by Linc and others, and that is they tend to bloom much sooner. One doesn't have to wait the usual five to ten years for blooming. I often admire the my English friends who, at the same age as I am, start putting out some of these treelike species, which they are lucky if their grandchildren get to see flowering.
Among the azaleas that I've been interested in largely are two groups. First of all, I was interested in David Leach's statement to the effect that Furbishi [Rhododendron x furbishii] is probably a hybrid between [R.] bakeri [now R. cumberlandense] and probably R. arborescens. I checked Lee's book on azaleas [The Azalea Book. Frederic P. Lee. 2nd ed. Princeton, NJ: Van Nostrand, 1965.] and he suggests that probably the parentage is either bakeri with arborescens or bakeri with a late blooming R. calendulaceum. I don't have any late blooming calendulaceum, but I do have what I think is a good arborescens and a good bakeri, so I made a cross between the two and flowered approximately 50 seedlings out of the 200 plants I have today.
I haven't seen any plants of furbishii grown in my area so I cannot make a direct comparison. As far as I can learn from the description of that species, I'm sure that Dave Leach is correct and that it is between bakeri and arborescens. It is a cross that comes relatively uniform. All mine were pink in some form or another and some with quite a distinct yellowish blotch. As a group they are very beautiful, combining the good features of both species and I think would be quite worthwhile. There is enough variation in them so that selection for better types would pay off, but I could say, if I were a commercial nurseryman, that I could probably expect to sell 99% of those seedlings under a grex name or a group name.
Another azalea that I've worked with is R. kiusianum. I haven't yet got many crosses with kiusianum with other species because I've been interested only in kiusianum itself. I was only able to secure one plant when I started a few years ago, and that was from Mr. Harold Epstein. He told me it was a selection from a population that he grew and that this was the best one that he selected. I'm not sure that it would be the best one for my area, so I proceeded to obtain kiusianum from other areas.
I found much to my chagrin that this one plant of kiusianum was partially self sterile or self incompatible, because I got relatively few seeds. Whereas when you cross it with almost anything else you get large numbers of seeds. However, by allowing whole plants to become selfed by bees either under protection or pollinated in the greenhouse, I have secured a fair sized population and within that population I can see quite a bit of segregation for diverse types. All of them have been white and all of them fit the general description of kiusianum. There is enough variation toward some very nice, compact, ground hugging types that I should like to continue with and, of course, I will cross it to various species in the future.
Among the dwarf rhododendrons, most of my work has been concerned with R. impeditum. Part of that is out of sheer orneriness. I have several British friends, and they make my hair stand on edge every time they tell me you shouldn't cross R. yakushimanum with anything because it's better itself than any hybrid could be. Well, I never made any crosses with yakushimanum with the intention of improving on yakushimanum necessarily, but to get some of the good features of yakushimanum into hybrids with species that are easier to work with in my area, and I think I'm succeeding along those lines.
Likewise, impeditum is a delightful plant in itself. But with me it doesn't flower well unless it's out in full sun. If it is out in full sun, it has a tendency to lose a good many buds in the spring or in the fall. This fall [1974] most of our bud elimination was done in October when the temperature dropped rather abruptly to 15 degrees [Fahrenheit] for three nights in a row, and I lost thousands of flower buds in many different crosses including impeditum. I don't know if there are any buds left that will open.
Impeditum, as you know, when grown in the full sun has the bad habit of starting to open a few flowers in the fall like most of the Lapponicums do, and that doesn't help it on winter hardiness. So I crossed impeditum. I should say that some of the European botanists who visit me say that it isn't impeditum but rather R. fastigiatum. They send me impeditum from Europe that is impeditum and it turns out to be no different from mine. It's the way they grow, I guess, but the fact is it is very difficult to distinguish. I think botanically speaking there is little difference between impeditum and fastigiatum because they integrate. The form I use is the one that was originally distributed by the National Arboretum, and I know many of you have that form. It's a very compact, easy to grow form.
I crossed that one to R. dauricum album, to R. mucronulatum variety 'Cornell Pink', and to R. racemosum. I got compact hybrids in every case. With dauricum album and with racemosum they were very compact, but they still grow twice as fast as impeditum. Although I don't know much about their flower bud hardiness as yet, they promise to give me something that is different. They are all sort of a nondescript bluish purple, but there are variations in that and I hope eventually to get that straightened out.
It isn't as easy as it may seem, because if we have cool weather they tend to come plum color. If we have warm weather they fade to a nice blue. This magenta color on top of the blue apparently is dependent upon low night temperatures for expression. Therefore, the color that I might put into a nursery catalog, if I did, might not agree with someone else's description of color that grew the plant further south.
The fact is that out of that group, and I grew two or three hundred plants out of each, I expect to select types that will be of interest, particularly the one between mucronulatum 'Cornell Pink' and impeditum. They tend to be somewhat larger growing with more variation in them, and a great deal of variation in foliage color as well. I am just as interested in a good foliage plant as I am in a flower plant. At the University [of Connecticut] we sell our surplus plants when we feel they are no longer of any use to us, and I have been astounded at the number of people who selected plants by the foliage, never mind the flowers. They point out very abruptly and very accurately that the flowers will last at least two or three weeks. The plant is going to be seen the rest of the year, and they want above all else plants with good foliage and that's what I'm aiming for, too.
Now with that in mind, of course, I like the types of plants that in the wintertime develop a bronzy color or change with the season. I have numerous hybrids from various dwarf types that early in the season are green, then become bronzy, become bright red in the winter, and then within the first one or two weeks of spring weather they turn back into green again. In my opinion this adds to the garden value.
In that connection I am particularly interested in a very dwarf mucronulatum. I secured some seeds from Epstein who had a plant from Japan. I've had seedlings now for eight years and they are only six inches high and a foot wide. They have terrific color so I think that form crossed with some of the other species is going to mean something. I don't think that the first generation will differentiate, because if you cross one with another species you tend to get the same kind of population as you would have between normal types.
The reason for that being that whatever causes the different forms in one species is not necessarily correlated with similar genes in other species. They tend to counteract each other so it makes little difference as far as the F1 plant is concerned in the first generation what plant you raise, but it sure makes a difference in the second generation and that's where we operate. In my opinion the time is virtually over when you can expect to get a good rhododendron from just crossing two species. You have to go further than that in order to get the types that you are really interested in and they have got to come from the second generation.
In some instances this would be a second generation made by selfing; in other instances it's going to be one made by sibbing, and sometimes you have to resort to other methods. This is because if you happen to raise a population between R. fortunei with something else, it's quite likely that the whole population will be rather nice to look at, but they won't have any pollen.
Male sterility seems to be a feature of fortunei hybrids and many of the fortunei in our area have no pollen. You examine them for their other characteristics and you will probably come to the conclusion that they are not true fortunei because all the fortunei that I have which appear to check out with herbarium specimens have pollen. Those that I buy, for the most part, in the trade (and most of those are labeled 'Lushan') have no pollen. Apparently the name 'Lushan' has been associated with hardiness in the Fortunei Group and so if you have anything that is hardy it is apt to be labeled 'Lushan' form. I have never been able to find out what that form really looks like but everything that I have gotten under that name has turned out to be male sterile, developing no anthers. But it does set tremendous quantities of seed even without pollination, meaning that the insects are quite busy.
One subject that was touched upon this morning by Mr. George Miller who said that at higher temperatures you are likely to get more seed. I think that's true though I wouldn't go quite as far as he did in making the statement that temperature and seed set are correlated. That implies the higher the temperature the more seed set or negatively the lower the temperature the less seed set. That isn't true.
What is true, however, is that any rhododendron, any plant I believe, sets seed best at a certain temperature for seed setting that we may call optimum temperature. It will vary with different generations, and it will vary with different species, and it varies with many other things. The studies that have been made in various Liliaceous plants suggest that it is directly related to the speed with which the pollen tubes can get down through the style and enter the embryo sac. For that reason I do much of my pollination in the greenhouse and I find, generally speaking, with the early blooming species I get much better results when I pollinate them in the greenhouse.
Occasionally that backfires because we have unusual weather in Connecticut and sometimes I move the plants into the greenhouse and everything is fine. Then we get 90 degrees weather on the outside and the greenhouse runs up to about 110 to 120 degrees. Then I have difficulties with the seed set again so you can't win for losing. The secret is, of course, to have plants in containers so you can move them about and work with some in the greenhouse and some out of doors. That saves a lot of time.
If you are hell bent on getting crosses and getting them to flower as soon as possible, it is not only good to have a greenhouse for pollination. It doesn't have to be a very good greenhouse, most any greenhouse will do. Then one can also grow the seeds under ideal conditions. Give the seedlings long days and flower some of these things that Linc Foster can flower in two years and I guarantee I'll flower in one year in the greenhouse. Now those seedlings will cost a great deal more so I have to balance the cost against other factors. The result is that I'll grow in the greenhouse only seedlings that I'm vitally interested in. I couldn't afford to do it with the big fortunei hybrids and so forth because even if I could cut five years off of these hybrids there would still be five years of greenhouse expense and that's too much. For species that you can flower early and readily, that of course helps.
Furthermore, we run into problems which I haven't solved yet, and that is whenever we make hybrids between Asiatic species we find that they grow very beautifully in the greenhouse. No matter what we do to them, long days, short days, high fertility, low fertility they still grow pretty well. Not so with R. catawbiense hybrids. If they are straight Rhododendron catawbiense, and I don't mean hybrid 'Catawbiense Album' but I mean the straight species, they are very obstinate. They often develop brown edges on the leaves as soon as the temperature reading isn't right. I suspect that catawbiense is very closely related to the particular climate in which it evolved and it isn't anywhere near as pliable as the Asiatic species.
We see the same difference when we compare the American species of azaleas with the Asiatic species. The American species of [deciduous] azaleas appear to be very strongly daylight controlled. They know when to stop growing in the late summer no matter how much fertilizer, how much water, how much mulch you put on.
Not so with the Japanese evergreen azaleas. If you water or feed them well or keep a heavy mulch on, they'll continue to grow regardless of day length until the first frost comes and kills them. Many of our commercial men have lost untold thousands of greenhouse azaleas the first night the temperature dropped below 32 degrees. When such azaleas are grown outdoors in my area it is best to take the mulch off in August so they will abruptly stop growing for lack of moisture and fertility, and then they are very hardy. If you push them way late into the season, they are very unhardy, if you will pardon the expression.
Now since much of my work is with interspecific hybridization, I would like to elaborate a little bit on Dr. Kehr's explanation on interspecific hybridization. I'm sure that between the two of us we agree, but he didn't have time to quite finish his exposition on the subject and I can well understand that. Speaking of interspecific hybridization is like trying to prove the old statement that a little education is dangerous education because you are sometimes forced to leave off at the point where, by implication, something else should take place which isn't likely to take place. If you will permit me, I will go to the blackboard and start from scratch, so to speak. Then if Dr. Kehr wants to comment on that later on, he can do so.
Generally speaking in studying interspecific hybridization in plants as a whole, they vary tremendously in their behavior. If you read all the textbooks on breeding, you will find that hybridity is normally equated with sterility. That isn't necessarily true. We know that some interspecific hybrids, hybrids between species which no taxonomist would even put together in the same Series [a closely related group of rhododendrons in the obsolescent Balfourian classification system], give us fully fertile hybrids. We also know, of course, that there are many species which you can't intercross under any circumstances.
So for teaching purposes, I have divided interspecific hybridization in two general groups. The reason why I stress interspecific hybrids so much is that pretty nearly everything that you do in hybridization within the Genus Rhododendron is apt to be interspecific hybridization rather than intraspecific hybridization.
Many people reading an elementary paper on Mendelism cannot understand why the data they get doesn't agree with that. Let me say at the outset that so called Mendelian genetics is to be expected in intraspecific crosses within the species. If we put four categories down, we have hybrids that give us full fertility in the first generation, one that gives us only partial fertility, a third group that gives nearly sterile, and a fourth group that gives us all sterile.
We'll soon learn that what is called sterility by one person may not apply to the next person because temperature and age of the plant have much to do with it. Mr. Edmund V. Mezitt of Weston Nurseries has had hybrids around for ten years and never gotten any seed pods. When they have some older plants they are getting seed pods, but they are not getting seed from young plants growing right next to them. So there must be something about old age. We've often heard that as the plant gets older it probably realizes that it shall be now or never. Not that the plant thinks in exactly those terms, but many plant breeders are beginning to notice that plants of a given age are more likely to give seeds than others. Then, of course, we have those that are simply sterile, and let's say again that's not an absolute term because Mr. Mezitt would have said his PJMs were sterile five years ago. Now he says that they are nearly sterile because he is getting some seed and this is very important.
When we make interspecific hybrids between different chromosome numbers we may get results that fall into these [four] categories. Rarely, full fertility when we make crosses between different species if they are different chromosome numbers unless we do something about the chromosome numbers. You remember that Dr. Kehr mentioned his tetraploid white evergreen azalea 'Banka'. Dr. Kehr crossed this to calendulaceum and got a fertile hybrid. That to me indicated that calendulaceum is a hybrid between two related species. Why? Well how do you think calendulaceum came about its increased chromosome number? Just double? It's an interspecific hybrid and has a doubled number from two distinct species. If those two species were closely related, they wouldn't get fertility in the first generation.
Let me illustrate, and I'll do it with an entirely different plant because I have more backup numbers to support my contention. I have some 70,000 seedlings to back it up with.
We wanted to cross Delphinium cardinale, a California species with red flowers, to Delphinium elatum. We used either the species elatum or hybrids of it that are common in the trade—Pacific hybrids, 'Blackmore', and 'Langdon', etc. They are all elatum hybrids. One has 2n = 16 and the other has 2n = 32.
When I was a graduate student I decided that in order to get hybrids that were fertile, we would have to double the number of the first to get it up to 32. Then crossing this doubled one with the other, we might get a fertile hybrid. My professor said: "No, you won't get a fertile hybrid." But I pointed out to him that a Dutch nursery had just crossed a Northern California species to another and did get a fertile hybrid. He said that was exceptional. I asked why and he said you figure it out! We eventually reasoned it out and I agree that he was probably right.
Elatum, which is tetraploid, is not autotetraploid. Autotetraploid is when a plant is doubled in itself, such as the azalea that Dr. Kehr has. Then there will be four chromosomes of each kind. In the case of azaleas there will be 13 times what ever you have. Twenty-six is the diploid number, 52 the tetraploid. There are 13 different kinds of chromosomes. Each occurs four times.
But there are only one or two cases known in nature where autotetraploidy has produced new species because the autotetraploids, in addition to being rather dominant in their appearance, are larger in every respect, heavier substance, take longer to mature, etc. They seldom make it within the time interval that is available to the diploid species. Furthermore, they tend to be almost sterile. It is most difficult to obtain any more than 60% seed set in a newly made autotetraploid compared to a diploid. So what is logical to assume here is that two species, both diploid 2n = 16, or doubled 2n = 32, form sterile hybrids. Sterile because the chromosomes most likely couldn't pair. That plant became doubled at some time. We know that happens many times in nature. If sterile plants are perennial, sooner or later they become doubled by Mother Nature herself. I didn't say how many years it will take to do it, but we have seen it often enough in culture that it does happen.
[At this point the transcriptionist notes that Dr. Mehlquist proceeded to explain this point using a blackboard and it became impossible to reproduce this portion of his talk.]
I'm not trying to discourage you, just pointing out that when you undertake to transfer a particular factor or gene onto a species, you are in for a long program because the species are millions of years old, and are the best that Mother Nature can come up with. You can't change that overnight.
Many people have been trying to produce red-flowered rhododendrons, including me. I crossed 'Vulcan' and 'Mars' with white catawbiense. I used 'La Bars White', 'Catalgla', 'Catanea'. It doesn't make any difference which one you use. I get the same hybrid: magenta pink every time. No variation. Many of them are good, so good that Mr. Mezitt said you could sell the whole batch in the nursery trade as seedlings and they would be better than those obtained by so called selfing, which means nothing more than open pollination of 'America', 'Nova Zembla', or what have you.
I would like to get back to a hardy red flowered rhododendron. I'm in the F1 generation now and if you were to visit my place now you would see some 40,000 seedlings that are reaching the flowering stage. You would see at least 2,000 seedlings of advanced generations of those two crosses. I doubt that you'll see a decent red there. There were some red ones last spring, but everyone was tender. I'm looking for one that is red and hardy. Those that were hardy were not red.
Why? Because the R. griersonianum that produced the red of 'Vulcan' and 'Mars' is not represented by one or two genes, but by hundreds of genes in a certain combination. Catawbiense alba is also represented by a large number of genes. There are many more genes than chromosomes.
Therefore, many genes are located on the same chromosome. There is no way in the world that you are going to separate them except if that chromosome breaks in the right place. We know there are chromosome interchanges taking place in every generation. But to get the break between the right two genes is a very slight probability, which means you have to grow an enormous number of seedlings in order to achieve your goal.
I am often puzzled by people who raise a great population of seedlings and then they keep 12 or 15 of the best. The rest they give to someone else who promptly forgets what they were and after a while you have nothing to show for your work. They would do much better to concentrate on one cross and grow a tremendous number of seedlings. The question that is often directed to me is how many do you have to grow to recover a certain desirable plant. You can't calculate that unless you know the number of genes involved. But it is sufficient to say that if you are trying to recover a hybrid between two species that involves 20 genes, you have to raise an enormous number of seedlings, a number that no one could grow them all in order to see the full potential of any cross.
This series of "The Breeders Talk" will continue with Dr. Mehlquist in the next issue of The Rosebay. I.D.
