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

Abstract

Common scab of potatoes is a disease, which is difficult to manage due to complex interactions of the pathogenic bacteria (Streptomyces 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 txtB 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 txtB gene copies in bulk soil, while at Vyklantice site it was associated with low txtB 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.

The effect of susceptible and resistant potato cultivars on bacterial communities in the tuberosphere of potato in soil suppressive or conducive to common scab disease

“…Specifically, the quantity and community structure of actinobacteria were connected to pathogen population and its interactions (11, 20). Further to that the quantity of pathogenic streptomycetes (based on numbers of txtB genes) did not change with soil suppressiveness or cultivar in tuberosphere and bulk soil, but in suppressive soil the number of pathogens decreased in potato periderm possibly due to both microbial interactions and soil chemical conditions depending on location (9, 21). In this study, however, the increased numbers of actinobacteria in periderm of susceptible cultivar did not correspond to pathogenic streptomycetes, so perhaps an antagonistic community of actinobacteria developed there as a response to pathogen infection, similarly as in Rosenzweig et al (8) or Tomihama et al (22).…”

“…Disease suppressiveness of Vyklantice soil L was shown in previous studies (9, 11) and since the soil has been regularly interrupted by cropping sequence over long time it can be considered naturally suppressive to the disease (2). In the current experiment, CS disease severity was assessed again in suppressive soil L and conducive soil H, under field conditions, but this time the significance of cultivar status was also investigated, by comparing two potato cultivars susceptible or resistant to CS.…”

“…The two fields differ in common scab severity by observations over 30 years, while their geological context, soil type, climate and management are similar. The fields were regularly planted under a four-year crop rotation system including rapeseed, clover, potatoes, and grains (wheat or oats) in the past two decades (9).…”

“…All potatoes were carefully pealed using a sterile potato peeler (taking approximately 1 mm thick periderm samples), peels were homogenized and mixed, and subsamples (1 subsample per plant) were taken for further analyses (‘periderm’ samples). Tuberosphere soil samples were collected no further than 3 mm from a potato tuber (for details see (9)). Bulk soil was collected at a distance of approximately 30 cm from the closest plant within each plot using a small sterile spade (1 sample per plot).…”

“…In our previous investigations, two sites (Vyklantice and Zdirec) from the Czech Republic, where CS suppressive and conducive fields occur next to each other were studied both in field trials (9, 10) and pot experiments (11). The CS suppressive character of the fields differed according to field location, presumably in relationship to local soil chemical properties (9). Potato cultivars susceptible and resistant to CS have different ecophysiologies, and they differ in chemical composition of the potato periderm, which may further influence microbial community structure (12).…”