The Amaryllis Manual (1958) pp. 113-116
Hamilton P. Traub

Henry Miniature Hybrids

INHERITANCE INVOLVING TWO OR MORE PAIRS OF GENES (POLYHYBRID)

It has already been indicated that Amaryllis species do not show great variation within the species. Barring mutations, only limited progress can be made by breeding within the species. However, it may be possible to cross distinct varieties within a species such as Amaryllis belladonna (type) scarlet-flowered, difficult to manage in pots, and the variety haywardii, carmine-flowered, more easily managed in pots. But even in such a cross, except in the direction of possible hybrid vigor, progress would be quite limited. Obviously, such a project would show less promise for plant improvement than the crossing of still more divergent parents as represented by different species.

Amaryllis species, like all other groups of this kind, are relatively true-breeding, self-perpetuating groups that differ from others in the genus by one or more heritable characters of sufficient importance to set them apart. Although plant species as a rule do not interbreed under natural conditions because of geographical or other isolating mechanisms, it is sometimes possible—often in Amaryllis—to cross them under cultivation. If such species are intercrossed, certain definite recombinations of traits may be expected in the second generation after crossing according to the principles of Mendelism. Some of these combinations, when two or more pairs are considered, may be new and so progress may be made toward the improvement of hybrid amaryllis from the breeder's viewpoint.

In order to illustrate the procedure, let us examine an example from the limited information about amaryllis genetics. It is known that the gene for shorter style length is dominant over that for extremely long style. This may be added to the fact that the gene for red flower color is dominant over the gene for greenish-yellow. In such a dihybrid cross, and crosses involving more than two pairs of genes, independent assortment of genes during gametic fertilization is limited by the phenomenon of linkage when the pairs of genes concerned are located in the same pair of chromosomes (see Goldschmidt, 1952; Dodson, 1956). Experimental evidence has shown that the two pairs of genes involved in the present example are located on different (non-homologous) chromosomes so that an independent assortment can operate. Thus, the following cross may be made in order to obtain individuals with greenish-yellow flowers and a shorter style:

Amaryllis belladonna (type) Amaryllis calyptrata
Flowers scarlet, RR Flowers greenish-yellow, rr
Style shorter, SS Style extremely long, ss

When these two species are crossed, all of the offspring in the first generation (F1) will have scarlet flowers and a shorter style, RrSs.

In the second generation (F2) obtained by selfing the individuals of the first generation, all sixteen possible combinations appear according to the laws of chance if a sufficiently large population is grown. Further information may be found in such texts as that of Goldschmidt (1952). For our present purposes it is sufficient to point out that four of these combinations (genotypes) will be true-breeding for two pairs of genes, including the particular combination, rrSS, thus giving expression to the phenotype with a greenish-yellow flower and a shorter style.

The next step will be to eliminate all of those individuals that may be discarded by visual inspection, that is, the phenotypes with red flowers and long style. The final step will then consist of selfing the remaining individuals and growing a third generation (F3) to flowering in order to identify those that breed true for the desired gene combination, rrSS. The individuals will be selfed, and care should be taken to label each and to keep accurate records of the progeny obtained from them. Individuals that belong to the wanted group with the genotype rrSS will breed true for greenish-yellow flowers and shorter style; these will be preserved and the others discarded.

In the example cited only two contrasting pairs of genes were considered. It is apparent that as the number of genes to be recombined in one individual is increased to three or more, the number of possible recombinations to be considered in the second generation will be correspondingly increased. In this, way the number of individuals to be grown in the third generation for the identification of the wanted new combination would have to be very greatly increased, and would soon become too large for practical purposes. The breeder will therefore necessarily consider a minimum number of gene pairs in any one breeding experiment. When the desired new combination has been fixed, he will rely upon continued selection to a standard in succeeding generations over a period of years to obtain greater uniformity in other traits such as deciduous versus evergreen habit, and in still other traits such as those listed in Tables 1 and 2.

HYBRIDIZATION FOLLOWED BY VEGETATIVE PROPAGATION

Up to this point it has been assumed that the breeder is interested in producing a true-breeding hybrid that he can reproduce from seeds. However, if the breeder were to rely exclusively on vegetative propagation to increase the seedling clones, it would make no difference what the second generation might produce. He would propagate as ramets, or cuttings, the seedling clones with the desired characters, including the true-breeding or homozygous, and nontrue-breeding or heterozygous individuals. He would not know which were true-breeding, but that would make no difference so long as vegetative propagation was used exclusively.

In order to illustrate such a breeding project, let us examine the cross Amaryllis belladonna var. haywardii X Amaryllis espiritensis that gave rise to the Henry Miniature hybrids. The objective was to obtain miniature evergreen hybrids with medium-sized, carmine colored flowers that could be easily handled in pots. The seed parent was fairly easy to manage under pot culture, and it had the evergreen habit and carmine flowers. The pollen parent contributed a small bulb, shorter, oblong leaves, small stature, and an abundant offset-producing capacity. Both had medium-sized flowers and this was naturally carried over to the first generation hybrids. However, the hybrid was more easily manageable under pot culture than the fairly easily grown seed parent, and this addition was apparently due to a more favorable combination of genes leading to hybrid vigor.

1. A TYPICAL HYBRID OF THE MINIATURE DIVISION. Amaryllis x henryae, originated in 1950 by Mrs. Mary G. Henry, Gladwyne, Pa.

The Henry Miniature hybrids are being propagated by vegetative means so that there is no need for making any attempt to obtain true-breeding individuals. However, most of the seedling clones are usually 2-flowered, very rarely 3-flowered. The seed parent used in the cross is normally 2-flowered, but very rarely produces 3-flowered umbels under optimum culture. This same tendency has apparently been carried over to the hybrid, but for all practical purposes the hybrid is 2-flowered. If 4-flowered umbels and other colors are desired in Henry Miniature plants, it will be necessary to make additional crosses with other species and hybrids in the hope of reaching these goals.

TABLE 2. Character expression (phenotypes) in the first generation Henry Miniature hybrids, Amaryllis X henryae, and its
parents. The genotypes are not indicated because second and third generation analyses are required for such information.

Amaryllis belladonna var. haywardii Amaryllis espiritensis Amaryllis X henryae
Plant fairly easy under pot culture Plant difficult under pot culture Plant easy under pot culture1
Bulb medium to large Bulb small Bulb small2
Bulb with medium to long neck Bulb without a neck Bulb with a short neck3
Offsets produced, few Offsets produced in abundance Offsets produced in abundance2
Plant evergreen Plant deciduous Plant evergreen2
Plant recurrent flowering Plant spring flowering only Recurrent flowering2
Leaf shape elliptic-lanceolate Leaf shape oblong Leaf shape oblong2
Leaf length long Leaf length short Leaf length intermediate3
Peduncle tall (tall stature) Peduncle short(miniature stature) Peduncle short (miniature stature)2
Flowers 2 per umbel Flowers 2 per umbel Flowers 2 per umbel4
Pedicels very long Pedicels shorter Pedicels intermediate3
Flowers medium-sized Flowers medium-sized Flowers medium-sized2
Flowers carmine-colored Flowers porcelain-rose colored Flowers carmine-colored2
  1. Plant is more easily grown than either parent, apparently due to hybrid vigor.
  2. One gene, or allele, appears to be dominant, the other recessive; but this hypothesis is subject to later revision if second and third generation analyses should prove otherwise.
  3. lntermediate, indicating that apparently there is incomplete dominance.
  4. Apparently homozygous for two flowers per umbel.