Reproduction in Crop Plants

Abstract

The breeding procedures that may be used with a particular crop species are determined by its mode of reproduction. This relationship will become clearer as the breeding methods used with the various crop species are studied in more detail. It may be illustrated here quite simply by comparing two common crop plants, wheat and corn, which differ in their pollination method. In wheat, a self-pollinating crop, pollen normally fertilizes the flower in which it is borne; no new genes are introduced during pollination that may affect the purity of a variety. The seed of an improved variety of wheat may be harvested and planted over and over again if, during its production, reasonable care is exercised in the maintenance of varietal purity. Contrast this with corn, a cross-pollinated crop. In corn the pollen-bearing organ is borne in the tassel and the seed-bearing organ is borne in the shoot. Pollen is transported through the air from the tassel to the portion of the silk extending from the shoot before pollination and seed production are consummated. The pollen may be carried by the wind for large distances, with seeds borne on a single ear of corn arising by pollination with pollen grains originating from many different plants, so there is a constant mixing of different genes for particular traits of the corn plant. This results in a different reproductive system operating in a field of open-pollinated corn than in a field of self-pollinated wheat. Without an understanding of the details of pollination, fertilization, and seed development for a crop species it would not be possible to develop orderly and efficient breeding procedures before initiating a breeding program. It is necessary that breeders become thoroughly acquainted with the details of the mode of reproduction in the particular crops with which they are working. Knowledge of the details of reproduction also provides a basis for understanding the mechanism of heredity in plants. Basically, it is from the knowledge of its genetic behavior that the breeding procedures for a particular crop species are devised. 16 J. M. Poehlman, Breeding Field Crops