How can roses be hybridized to produce new varieties?
The hybridization of roses has the potential to produce new varieties with desirable traits, e.g. color, fragrance, hardiness, resistance to diseases, etc. The process of producing a new hybrid is laborious and time-consuming but is technically easy and can be learned by any dedicated amateur. The basic techniques of isolating pollen from one plant (the father) and using it to pollinate another plant (the mother) are well known and have been used for centuries to produce new varieties in many plant species. Newer approaches using genetic engineering offer the possibility of simplifying the process of introducing new traits into plants, although these methods are only in their infancy.
Traditional hybridization methods
- First, it is important to pick parents that are known to give good results in hybridizing. This is because the seeds of some rose varieties do not germinate well. The Marin Rose Society lists recommended seed parents. It also lists pollen parents, but these are not so critical.
- Start your hybridization efforts in the spring as soon as the roses have started to bloom. Choose flowers that have not fully opened.
- Remove the petals from the father bloom and remove the stamens. These are the male parts that surround the central pistil (female organ). Place the pollen sacs on a sheet of paper indoors while the sacs ripen and release their pollen.
- At the same time remove the petals and the pistils from the mother rose. Wait for a day or more until the stigma on the tip of the pistil becomes sticky. Then, using a small brush, transfer the pollen onto these structures. Place a label around the stem showing the name of the mother (first) and the father (second). It may be wise to protect the pollinated flower from birds etc. with a suitable cover.
- When the hips mature (usually indicated by turning yellow or red), harvest them and keep them in the dark for about a month. The seeds can then be removed and sown in a tray of vermiculite and sphagnum moss and covered with a layer of sand.
- The seeds will germinate after about 2 months. When they have matured into seedlings, they can be planted in potting soil and grown under lights or in a sunny window. The plants will bloom in a month or two and can be evaluated at that point, or the plant can be grown further and evaluated for other characteristics.
Genetic engineering approaches
Using genetic engineering to hybridize roses is not for the amateur gardener, but the technique is interesting and worth knowing about. It allows the introduction of new genes into a plant, thereby giving it a new characteristic that it didn’t possess previously. The most common technique for introducing new genes is using a plasmid (circular DNA) called Ti from the crown-gall-inducing bacterium Agrobacterium tumifaciens. The sequence for the new, desirable gene is introduced into the plasmid, and the modified plasmid is used to infect the parent plant. This reprograms the plant's cells by transferring new genetic information into the plant’s genome. Transgenic plants (plants containing foreign genes) will transfer the foreign gene to their progeny, thus ensuring a continued supply of the new variety. Traits governed by a single gene can be introduced relatively easily, but many desirable characteristics are coded by several genes and so are not easy to change.
The most successful use of genetic engineering in roses so far has been to produce a blue, or blueish, rose variety. This had been attempted but never accomplished using traditional methods. The new color was created by transferring delphinidin (a blue pigment) from a pansy into the 'Cardinal de Richelieu' rose variety. To get a good blue color it was also necessary to inactivate the gene coding for red color (cyanidin). The resulting rose is an attractive shade of mauve.
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- Courtesy of NYBG Plant Information Service