RHA Newsletter 5(3):
NOTES ON SEEDLING SELECTION
Dr. Griffith J. Buck
Pressures engendered by limited greenhouse facilities, growing areas and pinched research budgets can be a potent temptation to select early and discard populations prematurely. Depending upon the crop with which one is working and the goals one has devised, early selection can be a means to an end. This practice becomes practicable when one is after color variants, fragrance, or selection for dwarfness or its lack, for these traits remain relatively constant from the first flowering through to maturity of the plant. Perhaps, too, the ploidy level of the population may help to make early selection possible since diploids tend to mature earlier than those with higher genome levels.
Other characteristics are more subtle and depend upon plant maturity for their maximum expression. Resistance (or tolerance) to disease, cold or heat, for example, are seldom fully expressed in a yearling plant. To insure that individuals possessing these desirable traits are not lost, one must maintain the population until it reaches maturity. In roses this can be as early as three years or as long as ten although five years is a practical unit of time. With Garden Geraniums (Pelargonium) tetraploids require an average of three years; diploids 18-14 months.
If one is attempting to ameliorate a previously unused species into a cultivated group; i.e., our use of both Rosa laxa Retzius and R. Fedtschenkoana garden rose traits were slow to appear and in many instances, the first bloom was not obtained until the seedlings were in excess of 5 years old. During this early period it was not difficult to select for tolerance to cold and to disease, remontant flowering, fragrant foliage because by the time the plants were old enough to flower, the ones lacking cold or disease tolerance were dead. Repeated back crossing to garden rose cultivars shortened the length of time required for the first flowering and increased the number of seedlings with the Chinensis (everblooming) habit as opposed to the once-blooming and remontant, repeat flowering or intermittent flowering types.
Precociousness in flowering is a desirable trait, but because of it many selections were made because of the desirable floral characteristics and discarded prematurely for either lack of winter hardiness or susceptibility to diseases. It is part of our growing practice to select, and propagate, seedlings during their first year of growth outside. The original plants are marked, but too frequently they are among the missing by spring. However, plants propagated from these selections and transplanted to the open as MATURE have wintered, without protection, for up to ten years. Along with the increase in hardiness with maturity comes such other maturity traits as tolerance or resistance to disease, foliage fragrance, plant habit and type of inflorescence. In garden geraniums, at least in the ISU strain, the 13 node cycle flowering trait is not expressed until the seedling plants mature. This has been the developmental pattern for the roses 'Music Maker,' 'Country Dancer,' 'Square Dancer,' and the as yet unregistered 'Hawkeye Belle,’ 'Prairie Star,' 'Virginia Reel,' and 'Hoedown,' and the geraniums 'Hazel,' 'Pearlie May Red,' and 'Marian.'
Another maturity trait of particular interest to the breeder is the matter of fertility. In roses and garden geraniums pollen fertility is present with the first flowering and selected individuals from populations with desirable pedigrees have been used as pollen parents when little has been known about them. Immature plants, both as seedlings or yearling grafts will set seed sparingly if at all. With maturity many "sterile" plants become good seed producers, often to a very high degree of prolificacy.