New Breeding Methods

Methods of breeding sugar beets, other than mass selection, have been investigated while that method was being used to produce and improve better kinds. The investigations open new vistas of progress.

We discovered lines of self-fertile beets that in their sexual reproduction would not follow the general pattern of cross-fertilization. The usefulness of these highly self-fertile beets for breeding purposes was increased when beets were discovered that produced no pollen themselves and hence needed pollen from other beets for their fertilization. These male-sterile plants can be fertilized by pollen from self-fertile beets, and so produce pedigreed hybrids. With the way thus open to produce self-fertile or inbred lines with characteristics that can be determined, the possibility has arisen that many desirable combinations of characters can be bred in pedigreed hybrids. Inbred lines must be produced and evaluated before desired combinations can be planned and developed.

An indication of the promising possibilities from pedigreed hybrids is afforded by the performance of one such hybrid that has been studied. S. L. 4108 was produced by crossing a vigorous inbred line with a male-sterile beet of fair quality and high resistance to curly top. Under conditions entirely free from curly top, S. L. 4108 yielded 513 pounds more sugar to the acre than the average of seven other leading mass-selected kinds. This excellence was due partly to high vigor and partly to greater resistance to a parasitic disease that, affects the petioles and roots. Under very severe exposure to curly top, S. L. 4108 proved as resistant as the most resistant variety now in commercial use.

We have another significant indication of the possibilities of pedigreed breeding. By studying the reaction between certain inbred lines of beets and the different strains of the curly-top virus, it was discovered that some of the inbred lines are immune to some of the virus strains. We hope that the same immunity will be found in hybrids made with these immune inbreds. None of the best commercial varieties now in use has such immunity.

Also possible is the production of varieties that have single-seeded, or unilocular, seedballs and kinds having bilocular seedballs. Inbred lines have been found with a high proportion of bilocular seedballs. These characteristics can be reproduced in pedigreed hybrids. Two-seeded seedballs would be inferior to single ones, but would be a big improvement over the mechanically segmented seed now generally used.

Certain inbred lines have shown a noticeably low bolting tendency. This fact brightens the prospect for breeding for general adaptation to conditions where nonbolting varieties are required, as with early fall and early winter plantings in California. Such plantings are necessary. In the Imperial Valley, for example, the summer heat is so intense that in this extensive, highly productive area sugar beets must be planted in the fall, grown through the winter, and harvested in the spring. The winters are cold enough, however, that varieties very low in bolting tendency are necessary. Varieties of 'higher bolting tendency were extensively planted there by mistake one year and in the spring the fields looked more like plantings for seed than for sugar production.

Greater uniformity in size and shape of beets and consequently better adaptation to harvesting machinery seems a likely possibility through pedigreed breeding.

Another approach to the control of curly top is unique, and perhaps has a point for many other farmers. It is through an ecological study of the vegetation in desert range lands where disturbances of the natural plant cover encourage weedy areas that serve as breeding grounds for the beet leafhopper. A large-scale disturbance of that kind occurred in several regions under the stimulus of high prices for food during the First World War. Later, many of the areas that had been under cultivation were abandoned and they were immediately invaded by annual mustards, Russian thistle, and other hosts of the beet leafhopper. Bad practices prolonged those objectionable early stages of the plant succession.

The factors in the restoration of the natural plant cover, plants like sagebrush and grasses on which the beet leafhopper does not breed, were sought in the investigation. We found that with adequate protection from destructive agencies—temporary farming and abandonment, fire, and excessive grazing—a grass cover will replace the leafhopper weed-hosts in 5 years. Cattle, incidentally, are not the only animals that may overgraze: The persistent, year-round feeding of large numbers of jack rabbits destroys more vegetation than we had realized. Large experimental plots in the desert, portions of old abandoned farms, protected from fire and the grazing of domestic animals, continued to produce crops of mustards and Russian thistle and consequently large numbers of beet leafhoppers—until jack rabbits were excluded. Then the desired change in plant cover began. Rodents sometimes thwart efforts to reseed the ranges with perennial grasses; such failures often are wrongly attributed to too little rain.

Good management of range land and farm land, besides helping to control curly top of sugar beets, by keeping the population of beet leafhoppers below dangerous levels, is highly important to several other commercial crops. Tomatoes and a good many varieties of beans, for example, would be produced in a number of areas if it were not for the frequent heavy invasion of beet leafhoppers and the consequent damage from curly top.