American Rose Magazine 4(1): 18-20 (Jan-Feb 1941) 12-13
The Fading of Rose Blooms
J. C. Ratsek
Horticulturalist, Texas Agricultural Experiment Station,
A. & M. College of Texas, Substation No. 2, Tyler, Texas.

Address at Annual Meeting, Oklahoma City, Oklahoma, October 22, 1940,

MOST rose varieties have a tendency to fade to a greater or less extent during the summer months and to deepen in color in the spring and fall. This fading has been considered to be due to the effect of intense sunlight or heat. Results of experimental work at Tyler would seem to indicate that the fading is not the result of intense sunlight and only indirectly due to the effect of high temperature.

In the spring of 1940, in connection with a pruning test, Talisman plants were pruned as follows: thinned to 2 to 4 canes, which were pruned to 4 inches; thinned, pruned to 12 inches; thinned, pruned to 20 inches; thinned, not pruned; not thinned, not pruned. When the first crop of blooms opened, there was a great difference in their color due to the various pruning treatments. The blooms of the 4-inch pruned plants were in general somewhat deformed because of insufficient petal expansion; the centers were large and dark brown and the petals were almost white. With less severe pruning the petals expanded more normally, the centers of the blooms became somewhat smaller and much lighter in color, and the color of the petals showed more and more of the red pigment. Those treatments with no pruning resulted in blooms that were deep red in color and of true Talisman form.

It was evident that the pruning was in some way responsible for the difference in color. It is a well-known fact that with the coming of cold weather carbohydrates stored in the plant in the fall as starch change to sugars, and much of this sugar is present in the wood as a protection against freezing. The carbohydrates remain as a sugar into the early spring and serve as a source of rapidly available food for the newly forced buds. When tops of bushes are severely pruned, much of the carbohydrate store is removed. All that is left is the little in the stubs of the pruned canes and in the roots. The newly forced buds must have and do use this for wood production-that is, growth.

Investigators working on the relationship of inheritance and color have already pointed out that flavins, the pigments which produce the yellow color in blooms, and anthocyanins, the pigments which produce the red color, are composed of carbon, hydrogen, and oxygen and are carbohydrates. Both flavins for the yellow and anthocyanins for the red color are present in Talisman blooms. What apparently happened in the case of the severely pruned plants was this: the drain made on the sugar stores for wood growth left insufficient carbohydrates for the development of flavins and anthocyanins and the blooms were white or pale pink.

ARM 4(2): 44-45 (Mar-Apr 1941)
Dr. Ratsek's Rose Culture Exhibit
No. 3. "Pruning Your Garden Roses." Plants show the effect of various heights of spring pruning on roses in the garden. Front planting on the left shows typical 4-inch pruning and thinning to 3 to 4 canes. The plant just in back shows the pruned plant as it would be in the garden in September. It produced 101 blooms. Plants to the right show thinning and 12-inch pruning. This pruning height produced 176 blooms up to September 1. The plants in the rear show no pruning or thinning. These plants grew to 6 to 8 feet high and averaged 276 blooms per plant. The first and second crops of blooms on the 4-inch pruned plants were white with dark brown centers. The first crop on the 12-inch pruned plants were pale pink, with yellow-brown centers. Blooms on the unpruned plants were a deep Talisman red and remained so throughout the blooming season.

A series of experiments was begun to test this theory. Stems were completely defoliated. Within four days, the blooms that developed were white to pale pink. If defoliated stems were fed with a sugar solution, the color was appreciably deeper. When blooms were shaded with brown paper bags the blooms were pale pink in color regardless of whether leaves were present or not. Apparently light as well as a supply of carbohydrate is necessary to develop the red color of the blooms. Stems with a varying number of buds from one to twelve were observed for several weeks. Some were on defoliated plants, others were not. One bud on stripped stems produced from white to palest pink blooms. Two buds on stripped stems opened white. For stems with leaves present, the blooms varied in color from a medium pink to a deep red. As more buds were present, the color became lighter and lighter until at 5, 7, and 12 blooms the petals were again pale pink to white. It was further found that when several buds were present on one stem, the first bloom to open was nearly always lighter in color than later blooms.

To determine whether similar fading would result in blooms of other colors, plants of Etoile de Hollande (red), Briarcliff (pink), President Herbert Hoover (two-tone), and Julien Potin (yellow) were defoliated. In all cases except Hollande the blooms faded to white or very pale pink or pale yellow. Hollande faded to a pale purple-pink.

Based on the above experimental results, it would seem safe to conclude that intensity of flower color in roses is correlated with carbohydrate supply. Any factor, therefore, that would tend to reduce the amount of carbohydrate would also reduce the intensity of color in blooms. Defoliation by black-spot is such a factor. A reduction of leaves necessarily means a reduction in carbohydrates since it is the leaves that manufacture the carbohydrates. This is probably the most important single factor in the garden and nursery to affect color and cause fading.

Experiments showed that it is not the only factor, for even though foliage was maintained on plants there was still a small but appreciable amount of fading in the hot summer. The probable explanation is as follows: photosynthesis increases in intensity with an increase of temperature to about 78°; growth increases in intensity with an increase of temperature to about 86°; beyond these temperatures there is a gradual slowing up of the two processes. During periods of hot weather carbohydrate manufacture begins to slow down while growth is still increasing in intensity. All carbohydrates made in the leaves would be used in growth leaving little for pigment formation and bloom color would be pale. As cold weather sets in growth is reduced materially while carbohydrate manufacture still continues at a high rate. A surplus of carbohydrate is formed that is stored in the canes and roots for the winter dormant period and the new spring growth. With this surplus, plenty of carbohydrate is available for pigment formation and bloom colors deepen in the fall.

Previous studies at Tyler have shown that a relatively large supply of carbohydrate is necessary to develop a bloom. When only one bud is present on a stem sufficient carbohydrate is manufactured by the leaves to develop both bloom and pigment and the bloom color is of normal intensity. If two or more buds are present, competition between them does not permit of full color pigment formation and blooms are faded. The first bloom to open having the most competition is palest. Later blooms on the same stem with the first bloom matured and no longer competing will be of deeper color. Disbudding should and will increase the intensity of color.

The evidence also seems to show that strong light is necessary for the full development of the color pigments in roses. During cloudy weather or when plants are grown in continual shade, there is usually a fading of color which would seem to bear out the experimental evidence. This effect of light does not seem to be connected with the carbohydrate supply since in the experiment only blooms and not leaves were shaded. The effect may be due to a photo-chemical effect either on the pigment itself or on some other material not part of the pigment but necessary for the production of the color, possibly an enzyme.