ARS | Publication request: Caught in the act: a field gone suppressive for common scab?

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: March 17, 2009
Publication Date: June 1, 2009
Citation: Wanner, L.A., Haynes, K.G. 2009. Caught in the act: a field gone suppressive for common scab? Phytopathology. 99:S138

Technical Abstract: Potato varieties are evaluated for resistance to common scab (CS) in fields with high CS disease pressure. Occasionally, disease pressure naturally declines in a CS nursery; this is termed disease suppression. We have data on severity of potato CS in a scab nursery in Maine for 6 years between 2001 and 2007. In 2007, the mean CS incidence and severity, as judged both by area affected and type of lesions, was markedly lower than in earlier years. We isolated Streptomyces, the cause of common scab, from scabby potatoes in all 7 years between 2001 and 2007. The ratio of presumably pathogenic isolates (containing genes for biosynthesis of the pathogenicity determinant thaxtomin) to isolates lacking this pathogenicity determinant shifted from about 4:1 to 1:1 between 2004 and 2007, suggesting that the new strains successfully competed with pathogenic Streptomyces in the potato rhizosphere. The competitors belong to different Streptomyces species and grow more rapidly than pathogenic strains. These species have potential for biocontrol of CS.