Effect of downy mildew on productivity of sugar beets, and selection for resistance

Abstract does not appear. First page follows.

Introduction

For many years downy mildew has been recognized as a serious disease of sugar beets in the coastal regions of California during seasons when climatic conditions favored the development of the fungus. Farther inland, before 1935, this disease was considered of only minor importance; but in 1935, 1936, and 1937 there were serious epidemics over wide areas in the lower Sacramento Valley.

This disease, caused by Peronospora schachtii Fuckel, has been known in Europe since 1852, but was first reported in the United States by R. E. Smith and E. H. Smith ⁽⁷⁾4 in 1911. During subsequent seasons downy mildew appeared sporadically in the coastal sugar-beet-producing areas. In 1926 and 1927 Bensel5 reported severe outbreaks in the Santa Clara Valley. Since 1930 the disease has appeared regularly in the Salinas Valley of Monterey County, the Santa Maria Valley of Santa Barbara County, and in Ventura and Orange counties. There were destructive outbreaks in the Salinas Valley in 1930, 1937, and 1938; moderate epidemics during other seasons. According to a 1937 survey by Mr. Suttie of the Spreckels Sugar Company, covering 3,721 acres, about 22 per cent of the beets were infected by the middle of June. In 1938, up to 80 per cent of the beets were infected in some fields in the Salinas Valley.