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Title: Aggressiveness of Streptomyces on four potato cultivars and implications for common scab resistance breeding

Author
item Wanner, Leslie
item Haynes, Kathleen

Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/17/2009
Publication Date: 5/19/2009
Citation: Wanner, L.A., Haynes, K.G. 2009. Aggressiveness of Streptomyces on four potato cultivars and implications for common scab resistance breeding. American Journal of Potato Research. 86:335-346.

Interpretive Summary: Common scab disease is a serious problem for potato growers, reducing the quality and market value of the crop. Scab is more serious in some parts of the USA than others. This study was conducted to determine the contribution of different species of the scab-causing bacteria and different potato varieties to the differences in this regional variation in scab severity. We discovered that both the species of bacteria and the potato variety affect the severity of scab disease. This means it is important to pay attention to what bacterial species we use when testing potato varieties for common scab tolerance. The information is also useful in choosing the best potato varieties to grow in a specific region.

Technical Abstract: Common scab, caused by several species of Streptomyces, is a serious problem for potato growers. Although the mechanism of pathogenicity, based on the phytotoxin thaxtomin, is presumably conserved among all pathogenic species, variation in aggressiveness of different isolates is well-known. In addition, regional patterns in the distribution of Streptomyces species have recently begun to emerge. To clarify the contribution of different CS-causing species and strains of Streptomyces to local differences in CS severity, four contrasting potato cultivars were phenotyped in response to Streptomyces isolates representing different species/strains and geographic origins. Differences were observed in the response of potato cultivars to a geographic collection of five plant pathogenic Streptomyces isolates belonging to two different species and a member of a second group of plant pathogenic species originating from a widely separate geographic region. The groups differed significantly in aggressiveness on at least one of four potato varieties. S. scabies and S. sp. IdX isolates of Idaho origin are less aggressive than an S. stelliscabiei strain, which is similar to other S. stelliscabiei and S. scabies isolates and strains in aggressiveness. The sum of all main and interaction effects among plant, pathogen, and environment that we describe accounts for only about half to 2/3 of the total variation in common scab phenotypes. Further information on the distribution and prevalence of CS-causing Streptomyces species, together with the recognition of specific interactions between pathogenic species and potato cultivars, could form the basis for more successful recommendations of suitable potato cultivars for specific growing regions. Appropriate selection of Streptomyces strain for specific potato cultivars is essential in accurate and reproducible phenotyping required for genetic studies of CS tolerance in potato.