Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/11/2006
Publication Date: 4/1/2007
Citation: Wanner, L.A. 2007. A new strain of streptomyces causing potato common scab. Plant Disease. 91:352-359. Interpretive Summary: Common scab is a significant and recurring problem for potato growers, reducing the quality and market value of the crop. There are no available chemical controls for the disease. Part of the explanation for new patterns of common scab incidence and severity reported by potato growers could be the presence of more virulent or more competitive strains of Streptomyces. During the course of a recent survey of plant pathogenic streptomycetes isolated from common scab lesions on potatoes from 21 locations in the US, a new strain of streptomycete was isolated from scabby potatoes originating in southeastern Idaho. Information on the evolution and spread of new, potentially better-adapted or more virulent pathogenic strains is useful for scientists developing methods of predicting and managing common scab.
Technical Abstract: Common scab is a serious disease of potatoes and other root and tuber crops, affecting the quality and market value of the crop. The disease is caused by a genetically complex group of gram positive soil bacteria in the genus Streptomyces. Although common scab occurs wherever potatoes are grown in the world, incidence and severity vary in different locations and years. A new strain of scab-causing streptomycete was isolated from scabby potatoes originating in southeastern Idaho. Research has supported a model of horizontal transfer of pathogenicity determinants among streptomycetes and the new Idaho strain has the hallmarks of the recently characterized Streptomyces pathogenicity island (PAI); it has genes encoding the synthetase for the pathogenicity determinant thaxtomin (txtAB) and for a second pathogenicity factor, tomatinase (tomA). The strain lacks a third gene characteristic of the Streptomyces PAI, the nec1 gene. The new strain has a unique recombinant type of 16s rDNA gene sequence, though it is closely related to other pathogenic Streptomyces species. Isolates of this strain are pathogenic on radish and potato, and were particularly aggressive on the susceptible potato variety Green Mountain. This new strain (with apparently different pathogenicity characteristics) represents additional complexity in the pathogenic strains available to cause plant disease in the USA.