Counter - Counter - Observations on Breeding Rhododendrons
David G. Leach, Brookville, Pennsylvania
Mr. Guy Nearing, in his entertaining article on breeding rhododendrons which appeared in the April issue of "The Quarterly Bulletin" attacks with a good deal of glee my views on this same subject as expressed in the issue of July, 1951.
Despite his uncomplimentary remarks about genetics, most readers will recognize that it is a very exact science employing tens of thousands of professional breeders in projects which have resulted in brilliant achievements among plants of commercial importance ranging from hybrid corn to rubber trees. If Mr. Nearing wishes to hold a convention of professional plant breeders throughout the world who agree with him they can be comfortably accommodated in a telephone booth. Should he be right, we must close our great agricultural experiment stations, the genetics departments in the universities of every nation on the face of the globe and end the research grants from eminent scientific institutions. Millions of dollars and some of the finest intellects in existence are being wasted, if we are to believe Mr. Nearing.
He infers that the methods I proposed will not produce hardy plants for our Eastern conditions. He complains that to self-pollinate decorum x auklandii "would have been futile, for not a single plant of the offspring would have been hardy."
I tried to be less provincial. I meant to establish the principles and I assumed that those of adequate capacity would adapt them to gain their goals for whatever climate might prevail. I understand that rhododendrons are bred on the West Coast, too. Is it necessary for all readers to be bludgeoned into submission by belaboring the obvious point that for Eastern conditions a fully hardy species or hybrid must figure in the parentage?
Mr. Nearing speaks repeatedly of beauty and remarks that "there is no gene for beauty." Really? This one looks to me like the old shell game of setting up the stuffed doll just to have the pleasure of knocking it down.
Mr. Nearing treads on dangerous ground when he says that rhododendrons breed toward a mediocre norm, which even he admits is a mystical conception from his private imagination. "The results . . . of crossing complicated hybrids tends to approach this (inferior) norm," he says. Mr. Nearing seems to be confused by the obvious fact that, in segregating generations, the number of plants with the mean characteristics inherent in their forebears will far outnumber the population of plants exhibiting the extremes of their heritage. Mr. Donald Hardgrove shares this same misconception. Writing in "The Rhododendron Yearbook for 1946" he says: "Many breeders... spend much of their efforts crossing named hybrids of complex parentage. The experience of those who have been breeding for many years has conclusively indicated that such crosses are worthless. In complicated breeding, rhododendrons tend to fall quickly into a sort of racial norm, with little variation and not much chance of anything good." This sentiment might fairly be described as an echo of Mr. Nearing's views. Well, what is the evidence?
It would be hard to imagine a more complicated assortment of mongrels than the Exbury azaleas. They are complicated hybrids thrice complicated and yet compounded by dozens of progressive crosses dating back far beyond the turn of the century. These, the finest deciduous azaleas in the world in most colors, are the "inferior norm" about which Mr. Nearing wails in the night.
More evidence? A few years ago Mr. A. M. Shammarello of Cleveland made numerous crosses among various of the standard commercial catawbiense hybrid rhododendrons, which certainly fit Mr. Nearing's description of "complicated hybrids." Three years ago, 3,500 of these seedlings came into bloom. Instead of Mr. Nearing's "inferior norm" there appeared 175 plants quite superior to either parent; 85%, of the balance were about the same quality as the parents; and only 10% were inferior. Now 175 fine plants out of 3,500 is 51/. of the progeny which proved to be improvements over the parents in both foliage and color of blossom. Even Mr. Nearing will admit that to be a pretty good score, better than any plant breeder has a right to expect. But where is this mythical "inferior norm?" And may we not with reason refuse to accept his statement that "the use of hardy hybrids seldom gives good results when they are crossed with each other?"
"The rhododendrons actually planted and generally popular are mostly bred in the nurseries of England and Holland," Mr. Nearing says. How right he is, and how badly he undermines his position that progeny of complex hybrids are worthless!
The vast majority of nursery-bred rhododendrons have been the result of mating extremely complex hybrids, as Mr. Nearing would have discovered had his research been a little more exhaustive. To name just a few, 'Armistice Day', 'Borde Hill', 'Britannia', 'C. B. Van Nes', 'Countess of Athlone', and many others equally well known, date back to 1890 when some of the old hardy hybrids were crossed with R. griffithianum . The progeny were crossed once again, in 1898, with other commercial hybrids of complicated ancestry to produce about 40 distinguished rhododendrons including those listed above, of a heritage so involved that it would be a major project to unravel it. And we must not forget that 99%) of the rhododendron hybrids growing in the eastern part of the United States today are themselves intricately mixed, and in large part from the Waterer nursery in England. Are these, the most popular of all rhododendrons, the "inferior norm" which Mr. Nearing gloomily prophecies as the result of crossing complicated hybrids?
I do not advocate crossing complicated hybrids but my position is far different from Mr. Nearing's. I know that the "inferior norm" is nonsense, and that fine results can be obtained that way; but I also know that better results can be obtained more easily and quickly through the use of modern genetic principles.
Mr. Nearing says that "if . . . interspecific hybrids are selfed,, we will have a series of intermediates between them and the inferior norm of the genus." I should like to see Mr. Nearing defy the law of gravity with equal imprudence!
If we self-pollinate such an interspecific hybrid as maximum x decorum we shall get plants ranging in hardiness all the way from that of R. maximum to the relative tenderness of R. decorum in this, the F2 segregating generation. We shall also get blossoms ranging in quality from those typical of R. maximum to those of the species decorum. If enough seedlings are grown, as Mr. Nearing should have discovered, we shall get blossoms of decorum quality and fragrance on a plant of maximum hardiness, or nearly so, and such a result realizes all of the progress inherent in this simple example, which is typical of the method I proposed.
Mr. Nearing cites a very ancient English nursery record of degeneration from inbreeding caucasicum album as evidence of the folly of such a procedure. The record is 102 years old, to be exact, and it seems to me to be reaching pretty far out for the support he needs so badly for his position. But I have looked up this record too, and I am at a loss to understand why Mr. Nearing did not go on to point out the outstanding results achieved by Messrs. Standish and Noble from inbreeding the hybrid called "caucasicum album." Among them is The Bride which still boasts a two star rating from the R. H. S. after 102 years of affection and devotion on the part of the British gardening public. Mr. Frederick Street, the present successor to Standish and Noble, writing in "The Rhododendron Yearbook" for 1949 said: "The Bride is a beautiful plant. (It has) a pure white flower with a green centre. The habit is compact and bushy, the foliage...is glossy and of good colour. It is a hardy plant. The origin of this plant is most interesting. Briefly, it is an inbred form of caucasicum album." In citing the experience of Standish and Noble, Mr. Nearing could scarcely have hanged himself more neatly!
For more modern evidence I propose the following: in 1951 I self pollinated catawbiense x discolor . The seeds were sown in January and as of May 10, 1952, the seedlings are at least as vigorous as the average of various progeny from cross-bred rhododendrons mated at the same time.
Mr. Nearing mentions the fortunate results of his cross of decorum x auklandii with several of the red catawbiense hybrids as "astonishing." Why "astonishing?" catawbiense x decorum is hardy under eastern conditions and this was merely a segregation of the semi-hardy decorum genes combined with the griffithianum flower size to produce in the intermediate progeny blossoms about the size of decorum and of a pink shade midway between the red of the one parent and the white of the other. It was exactly what a geneticist would expect. And they are exceptionally fine rhododendrons. But Mr. Nearing, drawing a moral from this experience which he regards as merely fortunate, then goes on to advise other hybridists to close their eyes, pull the trigger on a few shotgun marriages, and hope for the best from whatever may be at hand in the way of breeding resources. Or to let the bees do it!
Such a recommendation may result in some good rhododendrons but it should be obvious that more scientific planning will produce far better results in less time with less effort than any such breeding by expedience as is here proposed. And it would be quite impossible to start out with the definite goal which every hybridist should have in mind and achieve it by any such informal mixture of hope and faith. I think Mr. Nearing is now growing seedlings from some brother and-sister crosses of these same fine rhododendrons which he mentions. This is a procedure which I recommended and which he derides!
After examining Mr. Nearing's other ideas about breeding rhododendrons I am alarmed that he should agree with me about the value of back-crossing, but he seems to think it has recently become popular in England mainly because seed parents for such back crosses are conveniently available. I doubt the motive of expedience which he attributes to our English friends who have exhibited in the past the most extreme care and attention to insuring the successful outcome of their hybridizing efforts. I was recently in Washington to attend the azalea symposium of the Department of Agriculture. Dr. Creech at Glenn Dale there outlined to me his proposed breeding program for the rhododendrons with which he is now working. He proposes to use back-crosses but the motive is certainly not expedience. He expects thereby to reduce the number of seedlings which must be grown to obtain the recombination of characteristics which he is seeking, a familiar procedure to geneticists as outlined in my article in the January "Quarterly Bulletin."
Mr. Nearing suggests ( dichroanthum x griersonianum ) x ( griffithianum x catawbiense ) as presenting a typical example of a good formula for producing a hardy rhododendron of high quality. I think such a cross would be a complete waste of the hybridist's time!
Before making any final cross the breeder working under Eastern conditions should certainly determine that the possibility of hardy progeny does exist. It is elementary that both parents contribute their genes in equal measure to their offspring. When the segregation of genes in such a cross of four species does occur, the hybridist in the East must ask himself the question "Will R. catawbiense crossed with either of the species, or a combination of them in the other parent produce hardy offspring?" For a possibility of success even to exist in Mr. Nearing's proposed cross, catawbiense x griersonianum , catawbiense x dichroanthum x catawbiense x ( dichroanthum x griersonianum ) must be capable of producing hardy progeny. And I think he will agree that none of these combinations will result in plants of sufficient hardiness to be widely useful in the Eastern part of the United States. If he concedes the latter, he must then concede the impossibility of such a cross producing a successful result.
But let's suppose that it could result in hardy progeny. It is still a poor method of breeding rhododendrons. The principal trouble with the proposed cross is that the hybridist must be content to take what chance may present to him. The breeder may get his hardiness combined with catawbiense color; dichroanthum flower size and truss formation; and griffithianum stature and plant habit. A more miserable failure could scarcely be imagined.
Every time the variables are increased through the introduction into the cross of additional species, the number of seedlings which must be grown to obtain the desired recombination of characters increases enormously. And manifestations of recessive genes combined in an undesirable manner increase in equal proportion. If we admit that this proposed cross is capable of producing progeny hardy for Eastern conditions, and that the ideal result is sought, we shall want (1) hardiness; (2) large flowers; (3) compact habit; (4) orange colored blossoms; and (5) a well formed truss. The number of seedlings which must be grown from a combination of four species to secure in one plant these five characteristics is not just five times the quantity which would be required were we to be content with just one desirable characteristic. It is astronomical.
But the principal objection to this proposed cross is that it permits no reasonable prospect of achieving a preconceived goal. There is no advance way of calculating the number of seedlings which ought to be grown, and there is no possible estimate of the likely manner of recombinations occurring. It is a wasteful, inefficient shotgun method.
Successful plant breeders of the 20th century working with plants of commercial value start out with a definite goal to be reached, and through the application of proven genetic principles, they achieve their aim or a reasonable approximation of it. Mr. Nearing's method offers no such possibility of mixing the cake to suit the taste. He proposes tossing into a bowl a dash of wanted ingredients, a surfeit of unwanted, turning on the mixer-"shaking Mendel's hat," he calls it-and hoping for the best.
Finally, Mr. Nearing recites with some pride his method of separating seeds of an authentic smirnowii x discolor cross from those of self-pollinated seed of R. discolor , all from the same capsule. Much as I admire Mr. Nearing's contributions to our cult, I did not know that his accomplishments included a Swami-like ability to foretell the future. I have seen seedlings from crosses of R. maximum develop to all outward appearance through six or seven years as typical of the seed parent with absolutely no evidence of hybridity, only to blossom with flowers of clearly hybrid origin. My admiration for his occult ability to distinguish hybrid from non-hybrid seed out of the same capsule therefore increases boundlessly.
But the methods I proposed for breeding rhododendrons are exactly parallel to those which have been employed by professional plant hybridists to achieve the innumerable noteworthy accomplishments in agriculture and horticulture the world over. There are no known instances where the basic principles of genetics have been invalidated in any field of hybridizing, from fruit flies to sugar beets. If Mr. Nearing thinks rhododendrons are unique in being outside the realm of physical inheritance, I think the burden of proof is on him.