Improvement of plants

All varieties of crop that arc grown have some desirable char­acteristics or they would not be used. Nevertheless, each of these varieties is known to possess one or more undesirable traits which, if eliminated, would result in higher yields and better quality. The aim of the plant breeder is to develop superior varieties by elimi­nating the undesirable characteristics and combining the desirable ones in the same variety.

The characteristics desired vary with the crop and the condi­tions under which it is to be grown. For example, with barley the characteristics that are considered by the plant breeder are malting quality and nature of the awns while what he desires with wheat may be winter hardiness, protein content and milling quality. In some areas, early-maturing, cold-resistant varieties are needed, while in others, later maturing, heat- and draught- resistant varie­ties will do best. In all cases yield and resistance to major diseases and insects are important.

The most important items which are of concern to the plant breeder are as follows:

1. Resistance to (a) diseases, (b) insects, (c) heat, (d) cold, and (e) drought.

2. Proper maturity.

3. Good yield.

4. Improved plant quality for (a) animal feed, (b) human food, and (c) industrial use.

5. Plant characteristics: (a) strength of straw or stalk, (b) height of plants, (c) shattering of seed, (d) leafiness, and (e) ability to re­cover following grazing or when cut for hay.

6. Adaptability to various soil conditions.

Introduction. Many of the important crop plants grown in the USA are not native to the United States. Actually many thousands of plants have been introduced from other parts of the world, but only a few of the best have been grown commercially. Over 8 000 introductions of wheat alone have been made into the United States. These and many others have been valuable not only from the standpoint of providing the farmers with new varieties that could be grown commercially, but, in addition, they have been a source of breeding material for use in the development of new, im­proved varieties. Marquis, Turkey, Kharkof, and Kubanka wheats, Manchuria and Oberbrucker barleys, and Kherson oats are illustra­tions of a few of the introduced varieties that played an important role in the agriculture of the USA.

Selection is a simple, but important method of improving plants. As the name suggests this method consists of selecting the outstanding types and discarding those that are undesirable because of certain characteristics being possessed by them.

For example, in small grains, plants resistant to lodging may be selected; and with alfalfa those capable of surviving in severe win­ters are to be retained. After a period of testing, during which plants are selected for certain desired traits or characteristics, a su­perior strain may be developed. Improvement by selection cannot be accomplished, however, unless the variety from which the se­lections are being made possesses some plants containing the char­acteristics desired.