Aggressiveness of Streptomyces on Four Potato Cultivars and Implications for Common Scab Resistance Breeding

Abstract

Common scab (CS), 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 in all pathogenic species, Streptomyces isolates vary in aggressiveness, and regional patterns in Streptomyces species distribution have recently emerged. We demonstrate that Streptomyces isolates differ significantly in aggressiveness, and there are specific plant genotype-pathogen isolate interactions in four contrasting potato cultivars treated with Streptomyces isolates belonging to different species and molecular types. There were significant differences between experiments, among isolates, among cultivars, and some of the two-way interactions were significant. The sum of all main and interaction effects among plant, pathogen, and experiment accounted for only 50–55% of total variation in CS disease symptoms. More information on specific plant-pathogen interactions combined with knowledge of the distribution of CS-causing species could form the basis for successful recommendations of suitable potato cultivars, and will contribute to more accurate and reproducible phenotyping required for genetic studies of CS resistance in potato.