American Rose Annual (1984) p. 37-43.
BREEDING THORNLESS ROSES
K. J. Nobbs
R.D. 2 TeKauwhata Road
Auckland, New Zealand

Editor's Note: Ken Nobbs has been hybridizing roses since 1973; now, at age 74 he has compiled an enviable record. He was formerly in Christian Missionary work in the Sudan in Africa. He founded Heritage Roses in New Zealand in 1980 and is a member of the New Zealand Rose Society Rose Breeders Association. He has hybridized fruits and some berries and is presently trying for a smooth, hairless, sweet, winter-hardy Kiwi fruit. For you Hybridizers out there, I have sent a report on his study of "Vitamin C in Rose Hips" (which I considered too technical for this publication) to Dr. Bob Harvey of RHA, to be used as reference material (per Mr. Nobbs request). The following piece, from an RHA Newsletter, will, I feel command your interest.

Unregistered seedling of Tausendschon, which the author calls Thornfree Glory

Botanically speaking, all roses are thornless. What we call thorns should, I suppose, be called bristles as they are superficial and, when young, are easily rubbed off the plant — being fixed to the bark only. Real thorns go deeper as one finds on the Hawthorn. However, rosarians and folk generally will always speak of thorns on roses.

There are degrees of thornlessness. Complete thornlessness is quite rare in roses; that is, the whole plant is without thorns on stems and under the midribs of leaves. There are rather more roses with thornfree stems but with those annoying hooks under the petioles. Sometimes these are barely perceptible. While in other plants they are very pronounced. Finally there are roses which have clean flowering stems and sometimes whole shoots without thorns but some large thorns at the base of the plant. In the case of Tausendschon, it is possible to have all degrees, from complete freedom from thorns to thorns only on the flowering stems.

One big problem for the hybridist is that most thornless roses are infertile as seed parents. Species roses often give us thornfree or near thornfree variants. Indeed, these may have to be the starting point as nature, generally speaking, has to make the first move and give us the gift of a thornfree plant.

It is edifying to observe how thornlessness came about in the cousin of the rose — the Rubus family. These blackberries, brambleberries and raspberries are as thorny as the rose as a rule. Breeding for thornlessness in brambleberries goes along with a desire to improve quality of fruit, fruiting capacity and freedom from disease in just the same way as we do in rose breeding, except that the emphasis in the Rubus family is on fruit, and in the rose, on flowers. No one today wants a thorny blackberry when he can have a selection of good cultivars with excellent quality fruits on plants free of thorns.

The problem for rosarians is that to date we do not appear to have genetically thornfree roses. Our thornfree roses, being sports, are liable to revert to thorns. Last year I discovered in Auckland a seedling rose of Mission Bells which was 100% thornfree and had been that way for seven years and was giving thornfree seedlings. I had no sooner written about it in the Auckland Rose Society monthly newsletter when this Spring, for the first time, it showed thorns. It may be interesting to note that this occurred after the coldest winter (still not severe by your northern standards) on record, and it just may be that this shock which the plant experienced, for the first time, may have induced a reversion to thorns. I have a list of roses which are considered thornless in the USA. Some of these have been imported into New Zealand but none of them are thornless here, while some have so many thorns that it is not funny. Here, again, may the shock of transfer to another hemisphere have triggered some defense mechanism to induce the plant to grow thorns? Another possibility to explain this reversion to thorns could be that the thornlessness in the plant — due to its being a chimera — may go deeper than the meristem. In this case, when buds are extracted from the parent plant they grow into the stock, the bud going into an area of the plant not changed by the sporting of thornlessness, and the new plant has thorns. Nurserymen have evolved for themselves thornfree stocks, for no one wants to work with thorny stocks. This has been done in western Australia and probably in Florida with the rose R. X fortuniana. This rose, thought to be a cross between R. banksiae (thornless in the double form) and R. laevigata, the Cherokee rose, produces for me shoots with thorns and at the same time, shoots which are quite smooth. Nurserymen, by selecting cuttings only from the smooth stems, ultimately in a few generations acquire a thornfree stock.

Mr. George Oliver of Slough, England informs me that he has arrived at the same result by propagating from smooth areas of the less thorny roses. In time, he has a thornfree plant and has growing together in his garden both the original thornless plants (with few thorns, that is) and the completely smooth stem version. It would be an interesting exercise for someone to try out this procedure with roses such as Iceberg, First Love and Pink Parfait, which are excellent plants with few thorns.

George Oliver, a dark horse unaffiliated with any Rose Breeders Association, has worked away for nearly 20 years in breeding thornfree roses and has grown 30,000 seedlings in his search for the thornless rose. He informs me that he believes, at long last, he has some genetically thornfree roses which, bred among themselves, will always give thornfree seedlings. He attained this goal eventually by turning to Ophelia, that greatest of all early hybrid tea roses with a wonderful capacity to sport which it passes on to its equally famous progeny. Although not itself thornfree, it has a capacity to give near thornfree plants. George Oliver believes that at long last, through Ophelia he has what the fruit breeders have acquired in blackberries — genetically thornfree plants. Oliver was able to produce a display of his thornfree roses in the autumn show in London in 1981. Contrary to what some rose breeders such as Sam McGredy believe, thornlessness is not color related and, indeed, Oliver has produced excellent dark red roses without thorns equally with the white and pink roses which, more often, are light on thorns.

*Basye (ARA 1985) crossed the very prickly Basye's Amphidiploid x Commander Gillette and got one seedling that was completely smooth.

Dr. Roberts of the East London Polytechnic has propounded the theory that thornlessness in the rose is due to cytoplasmic causes just as Dr. Griffith Buck informs me aromatic foliage in the Sweet Brier R. eglanteria is also. Of some 100 garden roses which have sported to become climbers, it is suggested these are also due to this cause. Dr. Roberts, in his article in the RNRS Animal for 1982 asked George Oliver to do an experiment by crossing a seedling of his without thorns with Fragrant Cloud. When the thornless seedling plant was used as seed parent, it produced three seedlings without thorns, but when Fragrant Cloud was used as seed parent with pollen from the thornfree rose, all seven seedlings had thorns. This experiment is obviously insufficient to prove a point, but it does give a strong lead and suggests that if anyone wishes to breed thornfree roses, they should always use the thornless plant as a seed parent.*

Royal Flush, LCl, a cross of Little Darling x Suspense. A good seed parent for thornfree progeny — a pillar-type rose.

I am working with Lee Fuller's lovely Royal Flush on which, on same sex plants, I have so far only found one thorn, except for those barbs under the petioles. As I am interested also in trying to hybridize to produce roses with fragrant foliage there is a problem: that if one must use either the rose with aromatic foliage as seed parent, equally with a thornless rose as seed parent, one cannot have both at once — unless the plant with the fragrant foliage is also thornfree. Most species roses with fragrant leaves are very thorny, but amongst some seedlings of R. Villosa (R. pomifera) I have a thornless rose. This is still juvenile and has to prove to be fertile. Another unfortunate thing is that this thornless species rose has less fragrance in the leaf than the plants I have grown from seed, which are normally bristly.

We need some thornfree species roses, especially roses such as the Sweet Brier, R. primula, R. villosa, R. setipoda (with three different fragrances in the plant) and R. multibracteata. I have found the Canina rose R. inodora which, while having little or no fragrance in its flowers, has the strong scent of apple in the foliage, as R. eglangeria has. A Sweet Brier rose found in our South Island by Dr. Malloy of Lincoln College is infertile. R. banksia roses, at least the double ones, both white and primrose yellow, are quite infertile. I have tried many times to hybridize the flowers without success. Two seedling plants from seed from the Shanghai Botanical Gardens began life with a few thorns, then quietly shed them. I await their flowering with interest.

Percy Wright tells me he has a thornless rugosa rose. I must ask him if it is fertile. If it is, it would be a valuable seed parent, for the rugosa has extreme hardiness, good health and remontancy so often missing in species roses. Rugosas, unfortunately, have a long juvenile period.

Now that a thornless miniature rose has been bred by Ralph Moore, and miniatures with moss buds are also available, the ultimate miniature rose must be one with fragrant flowers, moss buds, no thorns and that forgotten fragrance of foliage. As Jack Harkness points out in his recent book Roses, the rose fragrance on foliage, as in the Sweet Brier, can carry farther in a garden under the correct atmospheric conditions than that of the flower. The ultimate miniature rose, with this lovely characteristic, sitting on the window boxes of millions living in vast cities, without gardens could, activated by rain showers, fill the room with fragrance. Marvelous!

Thousands and thousands of people will not grow roses because they don't like thorns. In this country one rose for every six people is sold each year. They are all thorny except for a few sold by two nurseries who sell old world roses. How much more popular would the rose become if roses of good quality and good health and completely thornless were available to the public at large. This is long overdue, and it is up to the amateur hybridist to do what the professional rose hybridists make no effort to do. That is, give the public a chance to have roses which a blind person could feel without discomfort.

Aversion to thorns can, with me, be largely seasonal. Facing the pruning of several hundred rosebushes, especially climbers, is daunting. When, however, that long and unpleasant task is finished and the last thorns have been extracted from under the finger nails, or the lacerations of nose and ears have healed, one's hostility slowly abates. In that non-flowering stage, when roses have their fresh, clean leaves, the soft and scarlet thorns of many roses are indeed handsome. Thorns are useful for identification; by and large, the disadvantages far outweigh any attraction they may have. When I come to cut rose blooms, I find myself trying to avoid those with heavy thorns and choose those with long, clean stems from which no thorns have to be removed.

I will go on growing the really great roses, old and new, irrespective of whether they are thorny or not, but if the flowers and plant are not of that high standard and have thorns, they will be eliminated in favor of the smooth stemmed roses. Increasingly, my selection of seedling roses, which I wish to retain, will be governed, all other things being equal, by those without thorns.