The control of common scab (CS) of potatoes includes resistant cultivars, specific fertilization, increase of soil moisture and chemical treatments. Yet, these management practices do not have common or reproducible results at differing sites. In order to determine the effects of soil organic matter, iron and pH on CS development, peat and DTPA-chelated iron were supplemented to pots filled with soil conducive for CS. All results were compared with the same data obtained for a suppressive soil, which has naturally low severity of CS and occurs nearby. Bacteria, Actinobacteria and the txtB genes from the biosynthetic cluster of thaxtomin, which is responsible for the disease development, were quantified by qPCR in tuberosphere soil and potato periderm. Illumina amplicon sequencing of bacterial 16S rRNA genes was performed for tuberosphere soils. Both peat and iron supplements controlled potato scab, and the combination of the two supplements reduced CS most effectively. The bacterial community was modified by all treatments but the highest number of operational taxonomic units (OTUs) changed towards the suppressive soil after the combined peat and iron treatment. It seemed that iron supplement supported plant defense while both iron and peat additions changed the bacterial community in favor of CS suppression.
Control of common scab disease can be reached by resistant cultivars or suppressive soils. Both mechanisms are likely to translate into particular potato microbiome profiles, but the relative importance of each is not known. Here, microbiomes of bulk and tuberosphere soil and of potato periderm were studied in one resistant and one susceptible cultivar grown in a conducive and a suppressive field. Disease severity was suppressed similarly by both means yet, the copy numbers of txtB gene (coding for a pathogenicity determinant) were similar in both soils but higher in periderms of the susceptible cultivar from conducive soil. Illumina sequencing of 16S rRNA genes for bacteria (completed by 16S rRNA microarray approach) and archaea, and of 18S rRNA genes for micro-eukarytes showed that in bacteria, the more important was the effect of cultivar and diversity decreased from resistant cultivar to bulk soil to susceptible cultivar. The major changes occurred in proportions of Actinobacteria, Chloroflexi, and Proteobacteria. In archaea and micro-eukaryotes, differences were primarily due to the suppressive and conducive soil. The effect of soil suppressiveness × cultivar resistance depended on the microbial community considered, but differed also with respect to soil and plant nutrient contents particularly in N, S and Fe.
Nature-friendly approaches for crop protection are sought after in the effort to reduce the use of agrochemicals. However, the transfer of scientific findings to agriculture practice is relatively slow because research results are sometimes contradictory or do not clearly lead to applicable approaches. Common scab of potatoes is a disease affecting potatoes worldwide, for which no definite treatment is available. That is due to many complex interactions affecting its incidence and severity. The review aims to determine options for the control of the disease using additions of micronutrients and modification of microbial communities. We propose three approaches for the improvement by (1) supplying soils with limiting nutrients, (2) supporting microbial communities with high mineral solubilization capabilities or (3) applying communities antagonistic to the pathogen. The procedures for the disease control may include fertilization with micronutrients and appropriate organic matter or inoculation with beneficial strains selected according to local environmental conditions. Further research is proposed to use metagenomics/metabolomics to identify key soil–plant–microbe interactions in comparisons of disease-suppressive and -conducive soils.
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