Bacterial Stem Blight: A spring foliar disease of alfalfa

Authors: Samac, Deborah - Debby

Submitted to: Forage Focus
Publication Type: Trade Journal
Publication Acceptance Date: 5/1/2023
Publication Date: 5/15/2023
Citation: Samac, D.A. 2023. Bacterial Stem Blight: A spring foliar disease of alfalfa. Forage Focus. May 2023:3-4.

Interpretive Summary:

Technical Abstract: In the spring of 1904, farmers in the mountain town of Gypsum, Colorado reported the occurrence of a serious foliar disease of alfalfa on their ranches. By 1906 the disease had spread throughout the valley with a loss in tonnage from the first cutting estimated at 80%. Several scientists at the Colorado Agricultural Experiment Station led by Dr. Walter Sackett, did extensive research on the disease, which was published in 1911. However, bacterial stem blight has not disappeared. Several years ago, farmers in northern California reported symptoms of the disease along with frost damage. Bacterial stem blight has been identified in northern California, southern Oregon, the Cache Valley in northern Utah, southern Minnesota, and western Ohio. Plants showing symptoms of bacterial stem blight have also been reported in very early spring in the Central Valley of California and as far south as Auburn, Alabama. The primary means of combating diseases in alfalfa is through use of genetic resistance. For bacterial stem blight, a high resistance was found in several older cultivars that have winter survival traits, although most modern cultivars have about 5% resistant plants. Several types of resistance appear to be found in alfalfa. Some plants appear to inhibit bacterial growth while others tolerate high pathogens loads without showing symptoms. To accelerate breeding for resistance, experiments to identify DNA markers associated with resistance and candidate genes involved in resistance are being done. A greater understanding of the disease will enable plant breeders to develop cultivars with improved resistance to this disease problem.