Methods of breeding onions

Abstract does not appear. First page follows.

Breeding studies with the onion were begun at Davis in 1923. At first, the object was to develop a more uniform strain of Australian Brown. As the work progressed, however, the program was gradually expanded. At present, besides the improvement work with this variety, attention is being given to the development of onions that will resist pink root, mildew, and thrips; to the selection of nonbolting strains of Sweet Spanish; and to studies of the way in which the scale and flesh color, foliage color, shape, and other characters are inherited. In all this breeding work, special methods have had to be developed. Those that have proved best at Davis may need modification in other districts. At Davis, climatic conditions are nearly ideal for onion breeding. During May and June, when the plants are in bloom, atmospheric conditions are usually very favorable for pollination: rain seldom falls, the days are generally bright, and there is no dew. The plants, consequently, can be enclosed with very little danger of mildew.

Development of the Inflorescence and the Flower

Usually the mother bulbs are planted in late November or in December. Toward the end of February, if the plants are dissected, the flower stalks can be distinguished just above the stem plate. Sometime during March, as a rule, they emerge from the surrounding sheaths. They elongate rapidly, the developing buds being protected under the bracts. Finally the bracts are ruptured, and a few days later the first flower of the inflorescence opens.