Robert M. Harveson, Extension Plant Pathologist Panhandle R&E Center, Scottsbluff
In a March article, I initiated the proposal that two major factors were responsible for the United States to consider producing and utilizing domestic sugarbeet seed rather than depending upon Europe as the seed source.
I hypothesized that the first factor was the first World War. Seeds were generally unavailable between 1914 and 1918 because the majority of the seeds previously used came from war-ravaged France and Germany.
For those who read the preceding article and are now precariously perched on the cliff wanting to know what that second factor was, I will reveal that it was a viral disease known as curly top. Around 1900, this disease was referred to as “blight,” and it emerged as a significant threat to the establishment of the sugarbeet industry in the United States, particularly from the western growing areas. For the next three decades, it could have, and very nearly did, terminate beet production.
This one disease was responsible for the closure of numerous processing plants throughout the western United States, similar to the sugarbeet cyst nematode’s influence on European production in the second half of the 19th century.
The pathogen is identified
Curly top was among the first viral diseases recognized in the 1890s, but it was not until 1915 that a leafhopper (Circulifer tenellus) was identified as the vector for inoculation of the pathogen and spread of the disease. Furthermore, the disease was not confirmed to be caused by a virus until the mid-1970s with the improvement of viral purification methods and electron microscopy, allowing the virus particles to finally be observed.
Breeding for resistance begins
Because of the continued crop failures, the U.S. Department of Agriculture (USDA) began a breeding program in the mid-1920s aimed at creating curly-top-resistant varieties for use in the intermountain West. USDA Plant Pathologist Eubanks Carsner was assigned to lead the investigations for this effort, and he began collecting seeds from individual surviving plants that expressed resistance within fields with high disease pressure. This method is referred to as mass selection, and by 1929 Congress had appropriated additional funds for continuing this line of research.
Approximately 100 pounds of seed accumulated from surviving plants between 1925 and 1929 were replanted in areas with known severe pressure. They were tested first in Idaho in 1930 and later in California and Michigan. The surviving offspring from these field tests became the line “US 1,” which averaged 5.5 tons higher than the European varieties. Seed from this line was then increased to serve as a source of resistance for subsequent breeding purposes.
US 1 serves as a parent for new varieties
This process successfully generated and increased enough seed that 55,000 acres were planted in 1934 with US 1 in curly-top-problematic areas of the West. Although the use of this new variety was fully recognized as only a temporary measure, it was still released in 1933 as the first curly-top resistant source for commercial production.
US 1 was quickly replaced by other superior lines, labeled as US 33 and 34. They were created from re-selections from US 1, and both proved to be more resistant than their parents. For example, in 1934 the average national yield was about 4.9 tons per acre, but by 1941 yields had improved to 13.5 tons per acre. By the mid-1940s, this disease no longer posed a serious problem to the beet sugar industry, and Carsner and his staff received the Superior Service Award of the USDA for this massive achievement.
Curly Top’s Legacy Remains
The highly successful creation of disease-resistant varieties removed the constant threat of complete crop failures and the sugarbeet industry returned to many production areas that had been previously abandoned due to continuous losses with the disease-susceptible European varieties. Prior to this, breeders were uncertain whether this trait could be transferred into new lines; thus the curly top disease has also served as an important stimulus for spurring new advancements in sugar beet production.
The extreme devastation caused by this viral disease resulted in a breeding program designed for producing locally adapted, disease-resistant sugar beets with home-grown seeds, and thereby saving the sugar beet industry in its infant stages almost a century ago.
Based on information from these sources:
Carsner, E. 1924. Studies on curly top disease of the sugar beet. J. Agric. Res. 28: 297-320.
Carsner, E. 1927. Sugar beet disease called curly top limits production. Pages 603-605 in: yearbook of agriculture.
Coons, G. H., Owen, F. V., and Stewart, D. 1955. Improvement of the sugar beet in the United States. Advances in Agronomy 8: 89-135.
Harveson, R. M. 2015. The bacterium of many colors. APS Press, St Paul, MN, 288 pp.
Panella, L., Lewellen, R. T., and Harveson, R. M. 2009. Breeding for disease and insect resistance. Pages 3-5 in: Compendium of beet diseases and pests. R. M. Harveson, L. E. Hanson, and G. L. Hein, eds. APS Press, St. Paul, MN.
Townsend, C. O. 1917. The present status of the sugar-beet seed industry in the United States. U. S. Dept. Agr. Yearbook 1916: 399-410.