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Title: THE PERFECT STAGE OF POWDERY MILDEW OF SUGAR BEETS FOUND IN IDAHO AND COLORADO

Author
item Hanson, Linda
item GALLIAN, JOHN - UNIVERSITY OF IDAHO

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2002
Publication Date: 2/1/2003
Citation: Hanson, L.E., Gallian, J.J. 2003. The perfect stage of powdery mildew of sugar beets found in idaho and colorado. Plant Disease.

Interpretive Summary: Sugar beet powdery mildew has been a significant problem in many areas of the U.S. since the first major epidemic in 1974. The disease has been caused by the asexual form of the pathogen. However, in 2001, cleistothecia, evidence of the sexual stage, were found, first in southwestern Idaho, and later in south-central Idaho and northern Colorado. This has implications for breeding for resistance to the disease and managing fungicide resistance, since the sexual stage provides a means of genetic recombination in this fungus.

Technical Abstract: Powdery mildew [Erysiphe polygoni DC (syn. E. betae {Vanha} Weltzien)] of sugar beet (Beta vulgaris L.) has been a significant problem in many sugar beet growing areas of the U.S. since the first serious epidemic in 1974. Disease has been attributed solely to the asexual stage of the pathogen in the U.S., except for one report of the perfect stage in a single field in the state of Washington coincidental with the 1974 epidemic. In August 2001, cleistothecia were observed in several fields in southwestern Idaho. The perfect stage was widespread and easily found. Subsequently, cleistothecia were found in September and October in multiple fields in three additional counties in southwestern and south-central Idaho and two counties in northern Colorado. A single host genotype is not required for perfect stage development because cleistothecia were found on 12 different commercial varieties in the two states and six breeding lines in Colorado. Because the ascigerous stage provides a means of genetic recombination, there is the potential for races of the pathogen to arise with greater frequency. This has serious implications for managing fungicide resistance and breeding for disease resistance to sugar beet powdery mildew.