Canadian Rose Annual pp. 69-70 (1960)
Hybridizing Limitations
Roy E. Shepherd, Medina, Ohio

IT is somewhat difficult to realize that the Rose family (Rosaceae) contains approximately 100 widely distributed and diversified genera of trees, shrubs and herbs. It includes among others, and in addition to roses, such well known and dissimilar subjects as the Spirea, Blackberry, Raspberry, Plum, Peach, Apple and Strawberry. Modern botanists have attempted to place a few of these in other families or to establish entirely new ones, but their endeavours have not been universally accepted.

Plant breeders have also made numerous attempts to cross different genera of the family in the hope that distinct and valuable plants may result, but nothing of great importance has been produced. Improvement within a genus has been accomplished, however, by crossing one member with another and to these endeavours we must credit the great variety of apples, roses, etc., that we grow to-day.

There is considerable evidence to support the thought that Nature has created several inter-genera hybrids in the past, but man's accomplishments in this field have been comparatively few. Many persons believe that the nectarine, for example, resulted from a man-made cross of the peach and the plum, but it is more probable that it is a sport, or mutation, of the peach as nectarine seeds often produce peach trees and vice versa.

Although several members of the Rose family have genital organs of similar anatomy Nature has established certain laws that prevent their inter-breeding. Were it not for these restrictions we might have a conglomerated assortment of freak plant material with little practical or esthetic value. On the other hand, there are many combinations that could give us something worth while if they could be effected. Perhaps, however, we should be satisfied with the rose as we now enjoy it, and not anticipate an apple tree bearing rose blossoms or a rose bush on which the blooms were followed by large luscious peaches. In all seriousness though there is a distinct possibility that science may eventually find means of effecting crosses that have failed previously, and inter-genera crosses within the Rosaceae group may become a reality. They should at least be interesting.

The writer has succeeded in budding a rose on to an apple branch and in crossing a rose with a member of the blackberry family, but the bud remained dormant and the seeds did not germinate. Dr. J. H. Nicolas, formerly Research Director for Jackson and Perkins, was more successful as he raised three seedlings of a cross between an apple and a rose. They were similar to the latter in general appearance but showed evidence of apple influence in the bark, foliage, and in the peculiarly coloured double apple-like blossoms. The latter, incidentally, were somewhat similar to those produced by Bechtels Crab but not as well formed or as large. The plants were barely remontant and after blooming they were inactive until fall when a second spurt took place. Further experience with Rose x Apple and Rose x Hawthorn crosses gave similar results and all proved to be sterile. They were therefore valueless for use as parents in further breeding along this line. Yes, Nature is quite insistent that man does not make 'hash' of her children, and perhaps we should be content with the beautiful supply of plant material she has given us. The ever-present challenge to create plants that are distinct from all others is so great, and intriguing, that man will probably continue to attempt crosses that now seem almost impossible; and who can say that he will not eventually succeed? Unfortunately plants have a tendency to transmit undesirable characteristics more readily than they do the desirable ones, and these hoped for inter-genera hybrids would probably produce blooms and fruits of inferior quality.

Insofar as roses themselves are concerned we still possess considerable unexplored possibilities within the genus. There are 333 somewhat distinct species of roses recorded in Modern Roses V, and but eight of these have contributed to the major types of garden roses. Surely the other 325 have some potential and this should undoubtedly be explored before we spend time on intergenera exploration.