Memoirs of the Horticultural society of New York. v. 3 (1926)
International Conference on Flower and Fruit Sterility

SOME STERILE AND FERTILE PLANT HYBRIDS
N. E. HANSEN

Agricultural College of South Dakota

* See Heideman (1895) regarding the sexual affinities of Prunus species.

During the past 31 years, devoted to the improvement of fruits, the writer has originated many hybrids. A brief mention will suffice at this time. Some species yield fertile hybrids with certain species, and sterile hybrids with other species.* The reason for this is not yet clear. But homozygous material in general gives better results than heterozygous material as in complex hybrids, where apparently the chromosome structure becomes too complex or inharmonious.

Prunus Besseyi x P. triflora. Highly fertile. Bears on one-year-old shoots from the bud in nursery. Example: Opata, Sapa. These are widely grown in our prairie Northwest. The South Dakota Sand Cherry is dominant in hardiness and in habit of bearing; the Japanese plum transmits quality and large size of fruit.

Prunus Besseyi x P. Simonii, Not hardy. Fruits sparingly. Tokeya, the only one named, was discarded.

Prunus Besseyi x P. americana. The named varieties, Sansoto and Cheresoto, are highly fertile. The quality not up to Opata and Sapa. This is to be expected as neither parent possesses high quality.

Prunus Besseyi x P. Pissardi (P. cerasifera purpurea). Fruits of no value and sparingly produced. But as ornamental shrubs with red leaves the varieties Cistena and Stanapa are popular in western gardens.

Prunus Besseyi x P. Armeniaca. Very shy bearer. Not of thrifty growth, rather slender.

Prunus Besseyi x P. avium. Growth very dwarf and plants soon perished.

Prunus Besseyi x P. Persica. Kamdesa, my hybrid of the Sand Cherry of South Dakota with the peach, is of special interest. It has shown fruit only once in its history. The flowers instead of one pistil, have two to six pistils. The pollen is sterile. In this connection should be recalled the sterile peach x plum hybrids that have appeared in various places.

Prunus Besseyi, F2 hybrids. All highly fertile, when as in my Tom Thumb and Oka, the pedigree is evidently three-fourths Sand Cherry and one-fourth Japanese plum (P. triflora).

One of my hybrids, combining four species, P. Besseyi, P. Simonii, P. americana and P. triflora, is nearly sterile. Selfing with plums I find very difficult.

Prunus americana x P. Simonii. My varieties Hanska and Kaga give choice fruit and are productive in mixed orchards. Inkpa, the sister variety, is not productive. All have the excellent quality and fragrant firm-fleshed fruit of the P. Simonii of China.

Prunus Simonii x P. americana. Tokata is larger in fruit and considered one of the very best in flavor. Needs good pollination to produce fruit. It is evident that P. Simonii gives high quality. Most hybrids must have good pollination in mixed orchards.

Prunus triflora x P. americana. The hybrids are all highly fertile. The fruit of my Waneta is two inches in diameter. The tree is very strong and vigorous in growth. Also the two sister varieties, Kahinta and Tawena.

Prunus americana x P. triflora. The many choice hybrids produced by others as well as myself are fertile and early in bearing and show clearly that these two species are mutually fertile.

Prunus Americana x P. domestica. These two species combine either way with difficulty. They are not valuable and are generally sterile so far as noted in my experiments.

Prunus nigra x P. triflora. The native plum of Manitoba, Prunus nigra, combines well with the Japanese plum and its hybrids. Examples, my Cree, Pembina and Ojibwa.

Prunus nana x Persica. The Siberian almond always gives sterile hybrids with the peach but they are desirable ornamentals. [Michurin's Posredinik was a fertile hybrid of Siberian almond and the peach, P. davidiana.]

Pyrus baccata x P. Malus. Thousands of hybrids have appeared since the Siberian crab-apple was brought to America. Pyrus Malus is considered by C. Koch to be a composite of six species, hence great variety is found in all the P. Malus hybrids. These hybrids are usually productive. When sterility is evident they are soon discarded. The best are of economic importance as a fruit for preserving. When too large they are not of importance, as they are too large for a crab-apple and too small for an apple. Some of the best crabs, like my Dolgo, are direct importations from Russia. The pedigree is not known. My Alexis crab which is very similar in every respect to Dolgo, was grown from seed of Pyrus baccata received from the Botanical Garden at Leningrad.

Pyrus Malus x P. baccata. My best so far is Maga crab, a hybrid of McIntosh apple with the Virginia crab (a hybrid crab). My Olga crab (Duchess of Oldenburg apple x P. baccata cerasifera) is highly fertile.

My Hopa red-flowered crab (P. Malus Niedzwetzkyana x baccata) is highly fertile. The fruit is small, but the tree is very ornamental when in bloom.

The longer I work with Pyrus baccata the more I am convinced that pure selection work should be done with this species. Apparently the best form is the most northern type so far available. The Nertchinsk seedlings from the Amur River region of eastern Siberia are wonderfully productive trees. Since my best South Dakota sand cherries this year are one inch in diameter, the product of selection through several plant generations, I believe that the pure Siberian crab, Pyrus baccata, can be developed to full apple size by selection only, without the hybridization with the cultivated apple, Pyrus Malus, which sometimes gives sterility or lack of winter hardiness.

Native American Apple. The wild west American apples Pyrus Soulardi and P. ioensis combine well with the cultivated apple, P. Malus. (Note my Kola, Zapta, Tipi and Shoko.) But the work is not finished as the wild crab acerbity is yet too much in evidence. My Anoka apple is very popular as it is of good quality and bears in one or two years after transplanting one year budded trees on one-year-old wood. It is from seed of the hybrid wild crab Mercer topgrafted on Duchess of Oldenburg. The tree is a remarkable annual bearer and remains semi-dwarf from its heavy bearing.

The Future Program for the Apple. If it is true that six species are in the ancestry of the cultivated apple, it would be an extremely difficult piece of work to reduce the apple to the homozygous condition, which is so desirable for F1 combinations. Homozygosity is the ideal of the apple breeder, but it appears very difficult to secure this judging from the experiments so far in several states. Many valuable varieties have been obtained by the use of entirely heterozygous material, but it would be well to go further and determine the results of using purely homozygous material.

Hybrid Alfalfas. Alfalfa is an old Arabic word meaning the best fodder. More and more alfalfa is becoming the great essential to successful farming over a large area of the United States. In Asia and southern Europe wherever the common blue-flowered alfalfa, Medicago sativa, and the yellow-flowered alfalfa, Medicago falcata, grow near together the hybridization takes place freely. Botanists call these hybrid forms M. media and the farmer calls them "Sand Lucerns." These hybrids are very numerous and consist of all sorts of mixtures in varying proportions of the yellow and blue alfalfa. As a class they are very productive and more desirable than either parent in vigor and productiveness.

Since Medicago falcata is very widely distributed in Europe and Asia, ranging in Asia from India north to above the Arctic Circle in northeastern Siberia, the plant varies greatly in its ability to resist cold, hence it follows that hardiness of this hybrid alfalfa must depend largely on the region from which it comes. Coming from the mild region of southern Europe it could not be expected to be as hardy as if it came from drier and more severe climates. Hence while nature has indicated in the Sand Lucernes a method of increasing the vigor of alfalfa by hybridization, we do not know, that any one combination is the best one that it is possible to make.

The strongest and best of these hybrid alfalfas is the one I brought from Russia in 1906 and named the Cossack. The small spoonful of seed which I brought over in 1906 has been developed in the hands of many farmers so that the 1916 crop in the western part of South Dakota was fully 1000 bushels and since then the acreage has steadily increased.

These hybrid alfalfas as a class are superior to either parents in vigor and productiveness. I have originated many varieties by alternate machine transplanting of one-year-old plants of two varieties as first noted in South Dakota Bulletin, 159, April, 1915. But pressure of other work has prevented their further development and propagation. South Dakota No. 1 and South Dakota No. 2 are the only two of this series of hybrids that have been distributed. The chief trouble is that the variable variegation in the color of the flowers makes it impossible to identify them. So their sale is entirely a matter of good faith. This need of a definite trademark led me to work for a white-flowered alfalfa.

This has been done in my white-flowered alfalfa and later in this present year, 1926, in my Hansen white-seed alfalfa, which has both white flowers and white seeds. It is the only alfalfa ever introduced that has a distinguishing characteristic so that it does not need certification or affidavits as to genuineness.

CONCLUSION

For further light in this matter it will be necessary to make all possible combinations of species. We will then know better what species are mutually congenial. To cross heterozygous with heterozygous parents is like aiming in the dark. But as Nature produces them in vast numbers, some good results are bound to be obtained. I favor using homozygous material as much as possible as greater hybrid vigor is obtained.