The ABC's of Hybridizing

by Roy E. Shepherd
(RHA Newsletter - Spring 1975)

...Rose breeding is a fascinating game of chance between man and plants, and luck is apparently an important element. However it is not all-important, as patience, perseverance and the ability to formulate a definite plan or objective are also prime requisites if success is to be achieved...

Briefly, have an objective - visualize the type of rose you would like to create and then study the material you have for use as parents. Eliminate those that possess undesirable characteristics. Unfortunately it appears to be far easier to transmit undesirable than desirable characteristics. The real skill required to become a successful hybridist comes not in simply applying the pollen of one blossom onto the stigmas of another, but in selecting the proper parents. Unfortunately all roses are not capable of producing seed or supplying functional pollen. Others may produce seed or poor germinative quality or have a positive tendency to pass on undesirable characteristics rather than good ones.

'Queen Elizabeth' 'Mount Shasta' 'Pink Favorite'
'Orangeade' 'Don Juan' 'Golden Showers'
'Little Darling' 'Helen Traubel' 'First Prize'
'Red Fountain'

Whether the pollen parent or the seed parent exerts the greatest influence in passing on certain characteristics to the progeny is a much debated question - reciprocal crosses should be made whenever possible. That is, make each cross both ways. (Pollen of A on B and pollen of B on A)

Having picked a well-developed rose, let us begin to study its anatomy by first removing the petals and sepals so that they will not interfere with our observation of the more important sex organs. Then use a sharp knife or razor blade to cut the remaining portion longitudinally to the center of the stem. We then find, exposed to the eye, the various organs of the flower in which the rose breeder is, at present, interested. The stamens or male organs, are usually quite numerous and form a complete circle around the pistils, or female organs. At the tip of each stamen will be found a small bi-lobed expansion or knob, which is referred to as the anther. The minute golden grains of pollen, (which are the male element or sperm), are produced in the anthers and are discharged as they ripen. The pistil may consist of one or many thread-like styles each of which terminates in a somewhat enlarged knob known as the stigma. Each style has at its base and attached to it the female cell, ovule or unfertilized egg. This ovule with others is enclosed in the ovary which is encased in a relatively large green cylindrical body known as the hip or fruit. Pollen applied to the stigmas, when they are in a receptive condition, is held in close contact by the sticky substance on the surface of the stigmas until the tiny pollen grains absorb sufficient moisture to begin growth. At this stage a slender thread-like 'drill', known as the pollen tube, bores its way down through the center of the style, in search of a tiny egg in the ovary. At the top of these (tube) is a tiny germ called the male gamete (reproductive cell), which escapes into the ovule as the 'drill' enters it and quickly locates and unites with the unfertilized egg.

The actual mechanics of rose breeding, from pollination to seedling care, consists of several operations. None require a great amount of mental or physical effort and each offers an opportunity to pleasantly anticipate what the ultimate results will be. Choose the male and female parents; from the former cut a flower bud (with about a 1-inch stem) that is almost ready to open and with the aid of a pair of tweezers, remove the sepals and petals. Put the remaining brush-like portion in a small container (jar lids are suitable); place it in a warm room, but not in direct sunlight. Within a short time the anthers will discharge their pollen and you have a ready-made brush with which to apply it to the stigmas of the seed-bearing parent. So much for the pollen parent.

The seed-bearing parent is prepared at approximately the same time you collect the pollen bearing anthers, and the buds should be of about the same degree of development. Simply remove the sepals, the petals and all of the stamens. After this operation of 'emasculation' has been performed, cover the remaining portion of the bud with a glassine or paper bag to prevent unwanted pollen from reaching the stigmas.

There is a difference of opinion as to the best time of day to pollinize. Some insist it should be done in the morning, others at noon, while a third group insists that best results are obtained if the pollen is applied in late afternoon; &the proper conditions may exist for from an hour or so to a day or more and is dependent, both upon the type or variety, of rose and weather conditions. It is evidenced to the eye by the appearance of a wet or glutinous substance on the surface of the stigmas. If this is apparent, the time has arrived to apply the pollen, but if the stigmas have a dry appearance they are either immature or too ripe. If the latter, discard the bud; in the former, postpone the operation until you are certain the stigmas are receptive. The time of year in which pollination must be performed is far more important than the time of day. Within a short time the anthers will discharge their pollen and you have a ready-made brush with which to apply it to the stigmas of the seed-bearing parent.

Be sure that you make your crosses early enough so that the seeds will ripen before cold weather. In Northern Ohio (Zone 5) pollinization is begun as early in the season as possible and ceases about the first of July. The hips commence to ripen about the middle of September and are harvested as soon as they begin to lose their normal 'growing-green' color or the stem begins to darken. Extremely premature fall usually denotes that the seeds are hollow and therefore valueless. Germination is somewhat more rapid, and better, if the seeds are not permitted to become too ripe and are not dried unnecessarily between removal from the hip and planting; both of these apparently cause the seed shell to become extremely hard, and delays or prevents the emergence of the cotyledons.

Previous to harvesting the seeds, some thought should be given to the media in which they are to be germinated...mixture of equal portions (by bulk) of soil, sharp sand and sieved peat moss...

Seeds are sown to a depth of about 3/16" in flats or pots and these are watered and place in a cool but not freezing location during the germination period&best at temperatures near 41 degrees. The seedlings of course, should be transplanted into individual pots and exposed to light as soon as possible after they emerge. They require light and greater heat to develop properly. They also require a richer soil than that in which the seeds germinated. The seedlings should be planted in the garden as soon as the ground can be prepared and the danger of hard frosts is past. They should be fed and watered generously. To assure survival during their first winter out of doors, the seedlings should be forced to maximum growth before midsummer and then hardened off, by withholding feeding and excessive watering. Germination often begins as soon as one month after planting (if planted outdoors) and will continue spasmodically until the advent of warm weather.

The influence of the pollen parent is apparent not only in the time required for germination, but also in the season of ripening, the number of seeds the hip contains, and to some extent, the size of both the seeds and the hip. This fact is apparent to anyone who has worked extensively with the species roses. In other words, do not discard seeds of a cross that have not germinated because other seeds borne by the same see parent have. There may still be hope if the pollen parent of that particular cross is a slow germinator.

I feel it is necessary to stress the importance of keeping an accurate record of all crosses. The record should begin at the time of pollinizing and should consist of the parentage, dates of seed harvesting, planting and first germination and seedling performance. The parentage is usually first recorded by attaching a tag bearing the name of the seed and pollen parents just below the hip when the cross is made. The seed-bearing parent should appear first.

Even the most ardent rosarian will admit - no known rose is perfect; none has all the qualities we desire. We have yet to gain the rose that is a heavy and continuous producer of well formed, fragrant blossoms of rich color, has good habit of growth, is disease resistant and is dependably hardy without protection in all sections of the country. All these characteristics are represented on one or more known rose, but are combined in no one variety...a goal toward which the amateur hybridizers should strive.

RHA Articles Page      RHA Home Page