The effects of two mineral and two organic acids, four organic solvents (methanol, ethanol, 2‐propano and acetone) and three inorganic metal salts in combination with temperature regimes 0 and 22C on the yield and resolubility of potato tuber proteins were studied. Using acids, the yield of precipitated protein ranged from 22.3% (citric acid, 0C) to 54.5% (acetic acid, 22C) of total protein; however, the resolubility was generally very low. The precipitation with organic solvents resulted in significantly higher yield as well as resolubility (P < 0.05) when precipitated at low temperatures. The yield ranged from 23.4% (ethanol, 22C) to 64.5% (2‐propanol, 0C) of total protein. The use of the salts resulted in precipitates with high resolubility regardless of the temperature regimes. The yield of precipitated protein ranged from 25.8% (ZnCl2, 0C) to 86.4% (FeCl3, 0C) of total protein. PRACTICAL APPLICATIONS The work studied the possibility of isolation of native potato proteins from potato fruit juice (PFJ) resulting from starch manufacturing process. Ethanol and FeCl3 were evaluated as the most promising precipitators for the recovery of potato tuber proteins from PFJ. However, ethanol usage for industrial isolation of potato proteins is strongly limited by the temperature regime in contrast to FeCl3, which could be used in a much wider range of temperature regimes without significant difference in protein yield and resolubility.

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.

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.

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SummaryConcentrations of Ca, P, K, Mg, AI, Fe, Mn, Cu and Zn were determined in healthy tuber peelings of cultivars less (Karin, Sant6 and Symfonia) and more (Agria, D6sir6e and Tomensa) susceptible to common scab when grown at two sites that differed in the level of scab incidence. The accumulation of some elements was significantly influenced by site, year, cultivar, maturity and the age of tuber periderm. At both sites, Ca and P in periderm tissue declined but Mg increased during the growing season. The Ca/P ratios in tuber periderm of all cultivars greatly decreased 83 days after planting. Concentrations of mineral elements measured at harvest may not reflect conditions present during the infection period, and consequently may not be related to scab incidence or severity.