Roses in the wild grow in reds, pinks, yellows and white. The dazzling color variations in a modern garden catalogue or florist shop have expanded the basics to include every color except blue. Rose color variations are achieved through genetics or environmental conditions. Selective or accidental breeding or the production of a sport on a rosebush may result in colors different from the parents, including variegations. Phototropic and thermotropic influences can result in interesting variations.
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Cell sacs in the petals of roses contain pigments, which are capable of absorbing, transmitting and reflecting white light. Just as with a paint box, the mixing of colors produces somewhat predictable results. The introduction of wild yellow roses into selective breeding programs resulted in the first known orange roses around the turn of the 20th century. The concentration of pigments or the variation in the pH of the cell sap will affect the resulting color of the rose. Trace minerals can have an effect on rose colors, too. Rose breeders take all these factors into consideration when selectively breeding for color.
Roses in the field are pollinated as are other plants, and desirably colored seedlings may result from these open crossings. William Baffin received its bright pink color from its parents as a result of open pollination. When an especially desirable rose color is observed from a chance seedling, breeders take very seriously the opportunity to test and develop the plant over several years to evaluate its eventual market worthiness.
A rose sport is a genetic mutation that occurs on the branch of a rosebush. This natural or environmentally induced event is unpredictable. Desirable sports are cloned and cultivated as possible candidates for market. Chicago Peace is a sport of the famous Peace rose. Found growing in Chicago, its bright, rich pink and orange coloration is much deeper and more intense than its parent. Autumn Sunset is a yellow rose resulting from a sport. It is similar in form to its orange parent, Westerland.
Phototropic and Thermotropic Influences
Light and temperature can greatly affect the color variations in some roses. Cooler temperatures enhance rose colors, with white or very light-colored roses taking on pink, apricot or yellow tones in cooler seasons. Heat washes out the color of some lighter varieties, resulting in pink or yellow roses fading to white or near white in the heat of mid-summer. The availability of sugars in the rose’s bud stage is affected by temperature and light, resulting in these environmentally induced variations in color. The hybrid tea Double Delight as is a white rose with cherry-red coloration in direct proportion to sunlight exposure. Some modern breeders, such as John and Robyn Sheldon, are actively pursuing these tendencies in their breeding program.