Table S1. Chemical and biological properties of the bulk soil, potato tuberosphere and periderm at Vyklantice site.

Table S1. Chemical and biological properties of the bulk soil, potato tuberosphere and periderm at Vyklantice site

Table S6. T-RFLP profiles of actinobacterial communities in the bulk soil and potato tuberosphere at Zdirec site.

Table S6. T-RFLP profiles of actinobacterial communities in the bulk soil and potato tuberosphere at Zdirec site

Table S3. Common scab severity.

Table S3. Common scab severity

Table S4. T-RFLP profiles of actinobacterial communities in the bulk soil and potato tuberosphere at Vyklantice site.

Table S4. T-RFLP profiles of actinobacterial communities in the bulk soil and potato tuberosphere at Vyklantice site

Table S2. Chemical and biological properties of the bulk soil, potato tuberosphere and periderm at Zdirec site.

Table S2. Chemical and biological properties of the bulk soil, potato tuberosphere and periderm at Zdirec site

Determination of Factors Associated with Natural Soil Suppressivity to Potato Common Scab

<div><p>Common scab of potatoes is a disease, which is difficult to manage due to complex interactions of the pathogenic bacteria (<i>Streptomyces</i> spp.) with soil, microbial community and potato plants. In Bohemian-Moravian Highlands in the Czech Republic two sites (Vyklantice and Zdirec) were selected for a study of common scab disease suppressivity. At both sites, a field with low disease severity occurs next to one with high severity and the situation was regularly observed over four decades although all four fields undergo a crop rotation. In the four fields, quantities of bacteria, actinobacteria and the gene <i>txtB</i> from the biosynthetic gene cluster of thaxtomin, the main pathogenicity factor of common scab, were analyzed by real-time PCR. Microbial community structure was compared by terminal fragment length polymorphism analysis. Soil and potato periderm were characterized by contents of carbon, nitrogen, phosporus, sulphur, calcium, magnesium, and iron. Quality of organic matter was assessed by high performance liquid chromatography of soil extracts. The study demonstrated that the suppressive character of the fields is locally specific. At Zdirec, the suppressivity was associated with low <i>txtB</i> gene copies in bulk soil, while at Vyklantice site it was associated with low <i>txtB</i> gene copies in the tuberosphere. The differences were discussed with respect to the effect of abiotic conditions at Zdirec and interaction between potato plant and soil microbial community at Vyklantice. Soil pH, Ca soil content or cation concentrations, although different were not in the range to predict the disease severity. Low severity of common scab was associated with low content of soil C, N, C/N, Ca and Fe suggesting that oligotrophic conditions may be favorable to common scab suppression.</p></div

Table S7. T-RFLP profiles of actinobacterial communities in potato periderm at Zdirec site.

Table S7. T-RFLP profiles of actinobacterial communities in potato periderm at Zdirec site

T-RFLP profiles of the communities of actinobacteria sampled at Vyklantice and Zdirec experimental sites from tuberosphere soil (A,B) and potato periderm (C,D).

<p>Sammon’s multidimensional scaling was based on Manhattan distance matrices calculated for the baseline filtered and normalized T-RFLP profiles. The symbols represent the profiles of actinobacteria at the fields with low (open symbols) and high (closed symbols) common scab severity.</p

Biological characteristics.

<p>Quantity of bacteria, actinobacteria (16S rRNA gene) and <i>txtB</i> gene in soil and periderm. Means and respective standard errors (gene copies per gram soil, log10 transformed). Significantly higher values are in bold.</p><p>Biological characteristics.</p

Site characteristics.

<p>Site characteristics.</p