Breeding for Food, Feed, and industrial Uses

G. F. SPRAGUE.

MOST of the cultivated species of crop plants have been modified by breeding procedures to increase their usefulness as food, feed, and industrial products.

Let us begin our survey with wheat, the cereal of major importance among those grown primarily for food.

Wheat was brought into the North Atlantic coastal area by the several groups of colonists. All the groups brought varieties characteristic of their points of emigration. Diverse types thus were available. The ones best adapted to the new country persisted.

The first introductions were supplemented by additional introductions made by the successive waves of immigrants. Some came to have major importance: Red Lammas in Virginia; Mediterranean, in the southern Corn Belt; Purple Straw, in the Southeast; White Australian, on the west coast; Turkey, in Kansas, Iowa, and Nebraska; and the durums, in Minnesota, North Dakota, and South Dakota.

The improvement of wheat has followed the sequence of introduction, selection, and hybridization.

Most of the older varieties were gradually replaced by newer combinations, which in turn were replaced by still newer developments. The result has been the development of higher yielding types better adapted to the environment of the area of their culture.

The major improvement has been in resistance to various production hazards. These include greater resistance to hessian fly, green bug, and other insects; a greater winter hardiness;stiffer straw; and a higher resistance to smuts and rusts.

Covered smut has been particularly bothersome in the Pacific Northwest, where it is a soil borne parasite. Sources of resistance are available now to all of the physiologic races of importance.

Achieving resistance to stem rust has been more of a problem. As resistant types have been developed and become established commercially, new forms of rust to which commercial varieties of wheat are susceptible have arisen by mutation, hybridization, or other means.

New sources of resistance have had to be located, and such resistance has had to be incorporated into commercially acceptable types.

The use of newly discovered sources of resistance and the newer breeding refinements afforded by chromosomal substitution techniques offer promise of still further improvements. Much remains to be done in clarifying host-parasite relationships and establishing the genetic and chemical basis for physiological specialization.

Dwarf wheats, developed in the Pacific Northwest, appear to have a much higher yield potential than varieties in commercial use in 1960. Plant breeders have started to transfer the dwarf characteristics to wheats adapted to other sections, but the work had not progressed sufficiently in 1961 to assess the value of this development.

POTATOES may have been introduced in early colonial times. They were grown in New Hampshire as early as 1719. Breeding work during the next 100 years was limited. New varieties began to be developed from seed about 1840. Most of the important varieties were developed from true seed.

Cultivated potatoes are tetraploid; that is, they possess four basic chromosome sets. Most varieties initially had a high degree of male sterility. Male fertile varieties and selections have been developed. Polyploidy three or more repetitions of the basic chromosome set is favorable or at least is not disadvantageous under conditions of asexual propagation. The presence of extra chromosome sets, however, complicates breeding and genetic studies.

Considerable progress has been made nevertheless in developing varieties that possess satisfactory resistance to such diseases as scab, early blight, and fusarium wilt, certain types of virus, and late blight.

There remains the task of combining all these qualities and other desirable attributes, such as adaptation, yielding ability, and cooking qualities, into commercially acceptable types.

A few diploid seedlings plants with two sets of chromosomes are found in some seedling progenies. Exploratory work has begun to determine whether breeding operations can be conducted at the diploid level. If this can be done, all breeding operations should be simplified. The main deterrent appears to be a high degree of male sterility and the lack of a satisfactory technique for resynthesizing tetraploids.

SUGAR has become one of the cheapest of our common foods thanks to a combination of breeding improvements, improved cultural practices, and improved extraction and refining techniques. Sugar is produced from both sugarcane and sugarbeets in the United States.

Cane has been grown for hundreds of years. Even the primitive tribes of today maintain a wide variety of recognizably different types, which undoubtedly arose largely by natural hybridization and selection.

When the culture of sugarcane expanded to commercial proportions, the types utilized were naturally occurring wild types or selections made by primitive man.

Following the usual pattern, diseases became of increasing importance as culture became more extensive. At first, to combat disease, one variety was substituted for another. The first sugarcane breeding stations were established in Java and Barbados in 1886. Previously there had been some question as to whether sugarcane could be propagated by seed.

Three species have 'been used for sugar production in various parts of the world Saccharum officinarum, S. spontaneum, and S. barberi. Improvement has been done by crossing desirable varieties within S. officinarum, or by crossing S. spontaneum or S. barberi with S. officinarum, followed by nobilization and selection. Nobilization consists in backcrossing to the "noble" canes, S. officinarum.

Various virus diseases, red rot, and root rot have been the major diseases. Considerable success has been achieved in developing resistant types. Sugarcane is a high-order polyploid (probably octoploid).

In plants that reproduce exclusively by seeds, the individuals that have a greater or fewer number of chromosomes than typical tend to be eliminated by natural selection. This relationship does not hold if the individuals are propagated vegetatively. This is the situation in sugarcane, and chromosome numbers may be 80 to 160.

A measure of the progress that has been made is that the yield of dry sugar per acre has increased more than 1,000 percent since 1844.

Approximately one-fourth of the sugar consumed in the United States comes from sugarbeets. This crop is of recent culture and may be considered as the direct contribution of plant breeding.

A German chemist demonstrated in 1749 that the sugar from beets and the sugar from cane are identical. The first factory for the commercial extraction of sugar from beets was built about 1800. Extensive breeding work with sugarbeets was conducted in Germany and France, from which we imported seed until about 1930.

The European varieties were susceptible to curly top virus and cercospora leaf spot. The continuance of the sugarbeet industry required that varieties resistant to these two diseases be developed. The development of U.S.

Number 1 (resistant to curly top) and the demonstration of the feasibility of the overwintering method of seed production provided the start of a domestic sugarbeet seed industry based on locally developed varieties.

Marked progress has been made since 1930 in the development of varieties adapted to the important producing areas and combining high yields of sugar with resistance to the worst diseases.

Major developments in production practices have lowered labor requirements. Machinery has been developed for the mechanization of harvesting operations and for the "shearing" of seed to reduce the seedball to a single-seeded condition. This reduced the labor requirements for thinning. The discovery and utilization of the monogerm type followed.

Both cytoplasmic and genic sterility exist in beets. These types of sterility differ in their mode of inheritance. Their utility in plant breeding lies in the fact that both types are male sterile. The male-sterile plants can be used as female parents in the production of hybrid seed and the commercial utilization of hybrid vigor without the cost and volume limitations that would be involved in the production of hybrid seed by hand pollination. Considerable progress has been made in developing and evaluating the necessary stocks.

EARLY research to improve tomatoes was done primarily by private breeders and seed companies. Considerable work has been done since 1910 by public agencies to develop varieties resistant to disease. Marglobe was one of the most important of the first wilt-resistant types. Progress has been made in developing special types for canning and for growing in greenhouses. F, varietal hybrids have become available for home and market gardens.

Because the hybrid seed is produced by hand pollination, the cost is too great for extensive commercial utilization. A number of genetic male-sterile types are available. They may be used eventually to simplify production of hybrid seed and to permit the commercial utilization of hybrid vigor.

Most of the varieties of peas grown in the United States were introduced from England. They were not well adapted to our climatic conditions, and we had to develop adapted types that would fill different requirements for canning and for the home and market gardens.

Progress has been made in developing varieties having the growth habit and features of pods and seed the two outlets require and in combining these with resistance to wilt, a serious disease of peas.

One of the first major improvements in green beans was the reduction in pod fiber the so-called stringless varieties. Diseases later became of major importance, and attention was directed toward the development of resistance to anthracnose, bacterial 'blight, rust, and mosaic.

Regional adaptation and the differing requirements for market gardens and canning have complicated the breeding problem, but progress has been made.

Of the several types of lettuce, the "crisp head" type is the one usually offered for sale. Once it was grown mostly in the Western States. Varieties resistant to mildew, brown blight, and tip burn have been bred.