New Ways With Seeds of Sugarbeets

DEWEY STEWART.

THE OLD method of producing seeds of sugarbeets was to grow vegetative plants one season, store them over winter in pits or field trenches, and reset them in the field the second year to let them seed.

Because it took so much work, the production of the seed cost more in this country than in Europe, and for many years the American beet sugar industry relied on the European sources of seed.

Research workers of the New Mexico Agricultural Experiment Station and the Department of Agriculture demonstrated in the 1920's that excellent yields of seed could be had in the southern part of New Mexico if the sugarbeet were grown on the seasonal schedule of a winter annual a plant from fall-sown seed that blooms and fruits the following spring.

The new method the winter-annual method was developed by J. C. Overpeck and his coworkers. It greatly reduced labor requirements and permitted complete mechanization of the field operations. It met the need for homegrown seed of disease-resistant varieties.

Seed was grown by the winter-annual method on 62 acres in 1932. More than 12 million pounds of sugarbeet seeds were produced on about 7 thousand acres in 1937.

The winter-annual method proved to be successful also in the Virgin River Valley of southern Utah, the Salt River Valley of Arizona, the Willamette River Valley of Oregon, and southern California.

We produced enough seeds for our needs and for export to Europe during the Second World War. More than 10 million pounds were shipped overseas in 1947, but the seed became a small item of foreign trade as soon as the European countries could reconstruct their own seed establishments.

THE SUGARBEET and other cultivated varieties of Beta vulgaris produce two to five or more flowers in dense clusters. The flowers cohere at the base and grow together during maturation to form glomerate fruits, which usually comprise as many seeds as there were flowers in the cluster. The dry, hard fruits are the "seed" of commerce and often are referred to as glomerules, seedballs, or multi-germ seed.

The first fruits formed on the spikes of the flowering sugarbeet are the largest. The size of fruit and the number of seeds per fruit get smaller toward the end of the branches. The fruits formed on the tips usually are single seeded.

Investigators have found sugarbeet plants that have a single flower in each axis of the entire inflorescence.

These plants produce single-seeded fruits, or monogerm seed. This characteristic is inheritable, and monogerm varieties of sugarbeets have now been developed.

The sugarbeet is a biennial plant and normally requires two seasons for the growth of seed plants.

When the sugarbeet is grown for sugar, only the vegetative phase of growth a rosette of leaves and the fleshy taproot that yields the sugar is desired.

The reproductive phase of growth, with the production of seedstalk and flowering branches, can be induced in vegetative plants by cool temperatures. This temperature effect is called thermal induction.

Length of day, or photoperiod, also influences the growth and development of the sugarbeet, and the effect of temperature and light as an impulse to reproductive development is referred to as photothermal induction.

The temperatures that favor reproductive development in sugarbeets are fairly well established. Temperatures above 70 F. favor only vegetative growth. With proper nutrition and protection from hazards, the sugar-beet can be grown vegetatively for several years. Temperatures near freezing greatly reduce metabolic activity and have low inductive effect. The most effective range of temperatures for thermal induction is 45 to 55 .

Most commercial varieties of sugar-beets require 90 to 110 days of exposure to inductive temperatures for reproductive development. In a district suited to the production of sugar-beet seed by the winter-annual method, therefore, the winters must be mild to permit survival of the plants, but the period of cool temperatures must be long enough to supply the photo-thermal induction required for reproductive growth the following spring.

If the sugarbeet is grown for sugar in a region where the photothermal effect is just on the threshold of inducing reproductive development, some of the plants will shoot seedstalks. A few may produce seeds. These precocious plants are bolters.

Bolters reduce yield and quality and increase the amount of trash to be handled in the field and at the factory. Varieties that resist bolting have been developed for use in northern regions and in southern districts where spring weather supplies high dosages of photothermal induction.

Breeding work to develop sugarbeet varieties usually is conducted in the region where the varieties will be used for sugar production. The level of bolting resistance established in the basic strains is maintained through seed produced in a manner that forces all parental plants into reproductive development. The district chosen for commercial seed production by the winter-annual method must supply the photothermal requirements bred into the variety.

Bolting-resistant varieties are grown chiefly in the Willamette Valley and in other regions that have relatively long, mild winters. Commercial seed of varieties of ordinary bolting resistance can be produced farther south.

As long as the breeder knows the photothermal requirement of the elite foundation seed and chooses the proper district for commercial seed production, no great change in the level of bolting resistance should result from one generation of increase by the winter-annual method.

Photothermal requirements for reproductive growth can be established rather precisely in varieties through breeding. It is important to maintain this varietal characteristic in the commercial seed supplied to the grower.

THE BOLTING resistance of a variety has definite bearing on regional adaptation for production of sugar and on the district in which seed can be grown by the winter-annual method.

If seed of a bolting-resistant variety is produced in a district where winter conditions do not force all plants of the population into flowering and seeding, there will be a natural selection toward a lower level of inductive requirement.

We can illustrate the remarkable manner in which different levels of photothermal requirement determine regional adaptation of varieties of sugarbeet and the choice of seed for planting by referring to the Imperial Valley of California and the Salt River Valley of Arizona.

The Salt River Valley has the largest acreage of sugarbeets for seed in the United States. This district, centering around Phoenix, in 1948 produced more than 11 million pounds of seed, with a germination of 93 percent, on about 3 thousand acres. With a lower demand for seed in later years, the production has leveled off at about 5 million pounds annually. All the seed is produced by the winter-annual method.

The Imperial Valley, which is approximately 250 miles west, 40 miles south (1/2 latitude), and 1,200 feet lower in elevation than Phoenix, produces more than 100 thousand tons of sugar annually from roots grown on approximately 40 thousand acres. The acreage is grown as a winter crop.

The sugarbeet is fall sown in both the Salt River Valley and the Imperial Valley. A considerable acreage is planted concurrently in September.

The products harvested from the sugarbeet in the two valleys are strikingly different, however.

The production of sugar in the Imperial Valley and seed in the Salt River Valley depends wholly on a level of bolting resistance that has been established and maintained in the varieties. Because of bolting, the seed produced in Arizona would be undesirable in the Imperial Valley. Conversely, varieties adapted to that region could not be grown by the winter-annual method in Arizona.

THE DEVELOPMENT of the sugarbeet, largely during the second half of the 19th century, attracted wide attention, because it was a sugar plant that could be grown in temperate climates. The desire for self-sufficiency in sugar led to the introduction of the sugarbeet in our pioneer West, where land for crops was plentiful but where sugar was scarce and expensive. Seed of the sugarbeet was imported from Europe along with machinery and technical knowledge as well.

European varieties suffered great losses in the irrigated districts west of the Rocky Mountains because of curly top, a virus disease. In districts east of the Rockies, leaf spot and root rot caused heavy losses in yield and reduced quality.

It became evident during the 1920's that European varieties were susceptible to American diseases of the sugar-beet and that disease-resistant varieties were essential to a continuation of a competitive industry in this country.

The first American variety with distinctive characteristics to reach commercial status was US 1, a curly top resistant variety that was introduced in 1933. The urgent demand for seed of US 1 was a major incentive to the establishment of the seed enterprise.

Other varieties were developed soon by the Department of Agriculture, State agricultural experiment stations, and plant breeders employed by beet sugar companies.

Disease-resistant varieties were available for our major sugarbeet districts as early as 1940. Seed of American varieties have been used almost exclusively in this country since then. The dependence of the American producer and processor on homegrown seed of disease-resistant varieties made the seed enterprise an integral part of our beet sugar industry.

HOMEGROWN SEED of adapted varieties has contributed greatly to high yields of roots.

The acreable yield of sugarbeet roots averaged about 10 to 11 tons during the decades European seed was used in this country.

Beginning with the introduction of homegrown seed of American varieties, the yield of roots has increased steadily. The national average since 1952 has been no less than 16 tons. The crop of 1959 averaged 18.8 tons an acre.

This achievement cannot be attributed entirely to homegrown seed of improved varieties. Homegrown seed of resistant varieties has lessened the disease hazards of the past and brought a stability of crop performance that encourages the grower to apply improved field practices.