Isolation and characterization of Streptomyces spp. from potato and peanut in Israel

Potato common scab (CS) and peanut pod wart diseases cause substantial economic losses every year in Israel. In this comprehensive study on the Streptomyces spp. population, isolates were collected during 2004-2016 from potato tubers with symptoms grown in Israel, seed tubers imported from Europe and from peanut pods with symptoms grown in Israel. A total of 142 isolates were characterized by PCR using three primer sets (txtA, tomA and nec1 genes) and by three pathogenicity tests. Seven species were identified among the isolates, S. bottropensis, S. europaeiscabiei, S. griseus, S. scabiei, S. sampsonii, S. turgidiscabies, and S. venezuelae. S. europaeiscabiei was the most dominant among isolates from imported seed tubers, while S. scabiei and S. turgidiscabies were isolated from tubers grown in Israel. Isolates originating from peanuts were significantly more virulent than those from imported seed tubers, as determined by a pathogenicity assay on radish plants. The presence of pathogenic Streptomyces was detected by quantitative PCR (qPCR) in 289 soil samples collected from 31 commercial potato fields with CS history. Eighty percent to 100% of samples collected from fields with a high disease incidence on tubers (50%) gave positive results in qPCR, whereas in samples collected from fields with low CS incidence (2%-30%) the qPCR results were very variable. Potato seed lots imported from Europe during 2008-2021 were found contaminated with CS symptoms at different levels on visual examination. The results of this study indicate that Streptomyces species, in particular S. europaeiscabiei, were introduced to Israel through seed lots imported from Europe.