Establishing the Seed Industry

Sexual reproduction in sugar beets depends on two environmental factors of primary importance, prolonged low temperatures that permit only very slow growth, and long days or long daily periods of light exposure. Varieties vary genetically in these reproduction requirements. Only those high in bolting tendency gave good seed yields in the warmer areas first developed. And if they were repeatedly reproduced there, natural selection eliminated those individuals that did not go to seed and the bolting tendency of the resulting varieties increased to a degree unacceptable in fields of beets grown for sugar production.

Research overcame the difficulties. The factor of temperature required Most attention. Early planting, proper fertilization, and right irrigation gave large growth of leaves in the fall to shade the soil and keep the beets comparatively cool through the winter. Deterioration of varieties in bolting tendency was avoided by growing the stock seed under climatic conditions of other regions that afforded complete reproduction. Such stock seed is used to produce only a single generation of commercial seed in the warmer areas.

The regions better adapted climatically were also found to reproduce satisfactorily the varieties so low in bolting tendency as to merit the designation "nonbolting varieties."

Thinning or spacing beets, a laborious, expensive operation in producing sugar, is undesirable in seed-growing areas where winter days are often warm. Leaving the plants thick to shade the soil and each other helps reduce the temperature. The process of thermal induction of flowering goes forward slowly under favorable low temperatures, but under high temperatures it is rapidly reversed. Spacing may prove economically practicable in seed districts where daytime winter temperatures are seldom high enough to reverse the reproductive processes. Better light relations for photosynthesis and more economical use of nutrients and water in the soil result if there is not too much crowding.

Disease factors have been encountered in the seed-growing areas, too. Curly top in the interior regions, several fungus diseases, and one bacterial disease in the coastal regions have required attention. Breeding for resistance to all these diseases offers the best control.

The production of seed was firmly established in the United States as a result of the need for multiplying American varieties resistant to curly top. The foundation for the method of growing seed generally used in this country was laid some years before we had varieties that resist curly top. In Europe, the beets are grown one season, dug, stored over winter, and set out in the spring. Our method is much less laborious. The seed is planted in late summer or early fall, the plants allowed to grow slowly over winter in place, usually without thinning, and the seed harvested the following summer. The method permits mechanized operations that eliminate much of the hand labor required in the transplanting method.

Growing beet seed has benefited the agriculture of the areas where the industry has been established. The soil fertility has been improved as a result of research on the soil requirements for sugar-beet seed production and by the residual effect of fertilizers applied for the beet seed crop.

THE AUTHORS

Eubanks Carsner is a pathologist in the Bureau of Plant Industry, Soils, and Agricultural Engineering. He has been a field leader of sugar beet curly-top investigations since 1917.

F. V. Owen is a geneticist in the Bureau of Plant Industry, Soils, and Agricultural Engineering. He has had an important part in breeding sugar beets for curly-top resistance since 1930.