& Gardens 2: 111 (1946)
Use of Embryo Culture in Rose Breeding
Walter E. Lammerts
Embryo culture of rose seeds is a difficult process because of the hard, bony exocarp of the rose seed, which makes it necessary to very laboriously dissect out the embryo with the use of a very sharp knife. Even a skilled operator can only do about 250 to 300 per day; nevertheless, because of the very rapid life cycle resulting from use of this technique, the operation is well worth while whenever varieties are desired which, because of the characters involved, necessarily can only be obtained after several generations of crossing and backcrossing. Thus, seed from crosses made in May can be embryo cultured by August and brought into flower by late October or November. Pollen from these may then be used in backcrossing to either one of the parents or outcrossing to some third variety having a desirable character which should be combined with those of the two original parents, and seed from this backcross will be old enough to embryo culture by February, and the small resulting plants brought into bloom by late April or May, thus getting two generations per year. In this way it is possible in several years to combine characteristics from several different sources which with the usual technique would take from seven to eight years. The method is primarily of value when a rose breeder is beginning some new project such as the introduction of black spot resistance from a variety very near the wild species Rosa wichuriana. In this case obviously several backcrosses to the commercial varieties are necessary in order to eliminate some of the undesirable features of the Rosa wichuriana parent.
One of the most interesting examples of a rose variety resulting from this technique is one called Debonaire, a very highly mildew resistant yellow rose which I developed at Armstrong's Nurseries. The rapidity with which this variety was developed was largely due to the saving of time in the initial stages by the use of the embryo culture technique.
[The importance of embryo culture in Iris was pointed out in an article by L. F. Randolph, in the Winter number, 1945, of PLANTS & GARDENS (Vol. 1, pages 241-246) Ed.]