Common Scab Research Articles

Nitrogen fertilizers activate siderophore production by the common scab causative agent Streptomyces scabiei.

Streptomyces scabiei is the causative agents of common scab on root and tuber crops. Life in the soil imposes intense competition between soil-dwelling microorganisms and we evaluated here the antimicrobial properties of S. scabiei. Under laboratory culture conditions, increasing peptone levels correlated with increased growth inhibitory properties of S. scabiei. Comparative metabolomics showed that production of S. scabiei siderophores (desferrioxamines, pyochelin, scabichelin and turgichelin) increased with the quantity of peptone thereby suggesting that they participate in growth inhibition. Mass spectrometry imaging further confirmed that the zones of secreted siderophores and growth inhibition coincided. Moreover, either the repression of siderophore production or the neutralization of their iron-chelating activity both led to increased microbial growth. Replacement of peptone by natural nitrogen sources regularly used as fertilizers such as ammonium nitrate, ammonium sulfate, sodium nitrate, and urea also triggered siderophore production in S. scabiei. The observed effect is not mediated by alkalinization of the medium as increasing the pH without providing additional nitrogen sources did not induce siderophore production. The nitrogen-induced siderophore production also inhibited the growth of important plant pathogens. Overall, our work suggests that not only the iron availability but also the nitrogen fertilizer sources could significantly impact the competition for iron between crop-colonizing microorganisms.

Balancing the scales: assessing the impact of irrigation and pathogen burden on potato blackleg disease and soil microbial communities

BackgroundUnderstanding the interaction between environmental conditions, crop yields, and soil health is crucial for sustainable agriculture in a changing climate. Management practices to limit disease are a balancing act. For example, in potato production, dry conditions favour common scab (Streptomyces spp.) and wet conditions favour blackleg disease (Pectobacterium spp.). The exact mechanisms involved and how these link to changes in the soil microbiome are unclear. Our objectives were to test how irrigation management and bacterial pathogen load in potato seed stocks impact: (i) crop yields; (ii) disease development (blackleg or common scab); and (iii) soil microbial community dynamics.MethodsWe used stocks of seed potatoes with varying natural levels of Pectobacterium (Jelly [high load], Jelly [low load] and Estima [Zero – no Pectobacterium]). Stocks were grown under four irrigation regimes that differed in the timing and level of watering. The soil microbial communities were profiled using amplicon sequencing at 50% plant emergence and at harvest. Generalised linear latent variable models and an annotation-free mathematical framework approach (ensemble quotient analysis) were then used to show the interacting microbes with irrigation regime and Pectobacterium pathogen levels.ResultsIrrigation increased blackleg symptoms in the plots planted with stocks with low and high levels of Pectobacterium (22–34%) but not in the zero stock (2–6%). However, withholding irrigation increased common scab symptoms (2–5%) and reduced crop yields. Irrigation did not impact the composition of the soil microbiome, but planting stock with a high Pectobacterium burden resulted in an increased abundance of Planctomycetota, Anaerolinea and Acidobacteria species within the microbiome. Ensemble quotient analysis highlighted the Anaerolinea taxa were highly associated with high levels of Pectobacterium in the seed stock and blackleg symptoms in the field.ConclusionsWe conclude that planting seed stocks with a high Pectobacterium burden alters the abundance of specific microbial species within the soil microbiome and suggest that managing pathogen load in seed stocks could substantially affect soil communities, affecting crop health and productivity.BWvw4eepooU5poSUC2MUy8Video

Proteomics fingerprinting reveals importance of iron and oxidative stress in Streptomyces scabies-Solanum tuberosum interactions.

The Gram-positive actinobacterium Streptomyces scabies is the major causal agent of potato common scab. The main pathogenicity factor is thaxtomin A, a phytotoxin that causes atypical cell death, although other secondary metabolites have been described to play a role in S. scabies virulence. Despite this, many aspects of the interaction between S. scabies and its primary host Solanum tuberosum L. remain to be elucidated. Intracellular proteins of S. scabies EF-35 grown in the presence of in vitro produced tubers (microtubers) of the Russet Burbank and Yukon Gold potato cultivars were extracted and analysed by electrospray mass spectrometry (ES MS/MS). Based on the results of proteomic analysis, iron quantification by ICP-MS and nitrite quantification using Griess reagent in growth media as well as RT-qPCR analysis of the siderophore pyochelin gene expression were performed in the presence and absence of microtubers. Hydrogen peroxide accumulation was also determined in the nutrient medium used for co-cultivation of bacteria and potato microtubers. Potato microtubers caused an increase in the content of bacterial proteins involved in stress and defense, secondary metabolism, and cell differentiation, as well as secreted proteins. Co-cultivation with potato microtubers induced the accumulation of S. scabies proteins implicated in siderophore pyochelin biosynthesis, nitrite production and oxidative stress perception and response. The increase in the abundance of proteins related to pyochelin biosynthesis was consistent with a significant decrease in the iron content in the culture medium, as well as with induction of expression of pyochelin biosynthesis genes. Elevated nitrite/sulfite reductase protein levels were associated with increased nitrite excretion by S. scabies cells in the presence of host microtubers. The increase in the levels of proteins associated with signaling and oxidative stress response could have been caused by the accumulation of ROS, in particular hydrogen peroxide, detected in the studied system. These findings show that interactions of S. scabies with living potato microtubers induce the production of secondary metabolites, defense responses, and protection from oxidative stress. This study suggests the importance of iron during host - S. scabies interactions, resulting in competition between pathogen and its host.

Biological Management of Common Scab (Streptomyces scabiei) of Potato

Biological Management of Common Scab (Streptomyces scabiei) of Potato

First Report of Streptomyces brasiliscabiei Causing Common Scab on Potato in China.

Severe typical deep-pitted lesions of Potato Common Scab (PCS) disease were observed in two locations in China, Dingxi, Gansu Province, and Shuozhou, Shaanxi Province, in 2021. Potato farms in Dingxi growing cultivar Huangxin 226 (26 hectares) exhibited a scab disease incidence of 10%, while cultivar Jinshu 15# (4 hectares) in Shuozhou showed a disease incidence of 30% (Fig. 1). During harvest, tubers displaying PCS symptoms were collected for pathogen isolation. To obtain pathogen isolates, surface-sterilized tuber tissue with scab lesions was ground in sterile water, serially diluted, and plated onto ISP5 agar medium plates (Handique et al. 2022). Five pure colonies of Streptomyces isolate were obtained, designated as ZRIMU1503, ZRIMU1502, ZRIMU1320, ZRIMU1321and ZRIMU791. Genomic DNA was extracted and sequenced using Illumina technology. Sequencing data of the 5 isolates were uploaded to NCBI GenBank and annotated (Accession numbers: JBBAYL010000000, JBBAYM010000000, JBBAYN010000000, JBBAYO010000000 and JBBAYP010000000, respectively) using the PGAP pipeline (Tatusova et al. 2016). Average Nucleotide Identity (ANI) values (97.52 %, 97.53 %,97.54 %,97.57 % and 97.52 %, respectively) indicated the identity of the five isolates to the type strain S. brasiliscabiei IBSBF 2867T. Additionally, pairwise comparisons of Digital DNA Hybridization (DDH) value (76.2%, 76.3%, 76.4%, 76.4% and 76.2% respectively) of all the Streptomyces type strains show the highest identity to S. brasiliscabiei IBSBF 2867T. Twelve housekeeping genes (acnA, atpD, dnaN, gap, gyrA, gyrB , infB, mdh, recA, rplB, rpoB, and trpB) were extracted from the genome sequence of the five isolates to construct a multi-locus sequence analysis (MLSA) tree. The evolutionary distance of the five isolates was constructed using MEGAX software (Kumar et al., 1994), along with other Streptomyces strains that are known to cause PCS. The resulting cladogram demonstrated the isolated strains clustered together with S. brasiliscabiei IBSBF 2867T (Fig.2). Koch's postulates were fulfilled by inoculating a perlite potting mix with spore suspensions of each isolate (104 CFU/ml), planting tubers (cv. Favorita), and reproducing PCS symptoms at harvest after three months. Negative control received water treatment. The plants were kept in greenhouse with 12 h of light per day and irrigated regularly. The experiment was repeated twice, once in April 2022 and again in April 2023. On harvest, all five isolates exhibited development of severe symptoms of PCS (Fig.1), while the negative controls had no lesions. The pathogen was reisolated from the lesions and confirmed to be identical to the original isolate by 16S rRNA gene sequences. To our knowledge, this is the first report of S. brasiliscabiei causing PCS in China. S. brasiliscabiei was identified as a new species to cause PCS in Brazil and was identified based on morphology, pathogenicity, and genetic features (Corrêa et al. 2021). Multiple pathogen-causing PCS has been recognized in China and a surge of disease incidence in potato fields has been reported (Handique et al. 2022; Wu et al. 2023). S. brasiliscabiei causes severe symptoms which makes potatoes unmarketable. The disease epidemiology of this pathogen needs to be investigated.

Virulence determinants are unevenly distributed within Streptomyces species and strains causing potato common scab in the province of Quebec, Canada.

Potato common scab is an important bacterial disease afflicting potatoes around the world. Better knowledge of the local Streptomyces spp. populations causing this disease is key to developing durable control strategies. In this study, we isolated 230 Streptomyces strains from scab-infected potato tubers harvested from commercial potato fields located across the province of Quebec, Canada. The genetic diversity of this collection was first studied using repetitive element-based PCR fingerprinting, and the genomes of 36 representative strains were sequenced using PacBio's sequencing technology. This enabled us to identify the strains to the species level, to study the distribution of previously characterized virulence-associated genes and clusters, and to explore the repertoires of putative plant cell wall-degrading enzymes. In parallel, the virulence of the 36 strains was evaluated using a potato tuber slice assay. The diversity was higher than previously reported, as eleven phytopathogenic species were found across the province. Among them, S. scabiei and S. acidiscabies were the most abundant as well as the most virulent. Strains belonging to these two species harbored numerous virulence determinants, including the thaxtomin biosynthetic gene cluster. By contrast, most weakly virulent strains lacked this cluster but harbored at least one known virulence determinant. The results obtained suggest that a higher number of virulence-associated genes and clusters in the genome of phytopathogenic Streptomyces spp. is associated with greater virulence. This study contributes to increasing the publicly available genomic resources of scab-causing Streptomyces spp., and expand our knowledge on the diversity and virulence of this important bacterial pathogen.

Exploiting Differential Signal Filtering (DSF) and Image Structure Filtering (ISF) Methods for Untargeted Mass Spectrometry Imaging of Bacterial Metabolites.

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry imaging (MSI) is a label-free technique, producing images where pixels contain mass spectra. The technique allows the visualization of the spatial distribution of (bio)molecules from metabolites to proteins, on surfaces such as tissues sections or bacteria culture media. One particularly exciting example of MALDI-MSI use rests on its potential to localize ionized compounds produced during microbial interactions and chemical communication, offering a molecular snapshot of metabolomes at a given time. The huge size and the complexity of generated MSI data make the processing of the data challenging, which requires the use of computational methods. Despite recent advances, currently available commercial software relies mainly on statistical tools to identify patterns, similarities, and differences within data sets. However, grouping m/z values unique to a given data set according to microbiological contexts, such as coculture experiments, still requires tedious manual analysis. Here we propose a nontargeted method exploiting the differential signals between negative controls and tested experimental conditions, i.e., differential signal filtering (DSF), and a scoring of the ion images using image structure filtering (ISF) coupled with a fold change score between the controls and the conditions of interest. These methods were first applied to coculture experiments involving Escherichia coli and Streptomyces coelicolor, revealing specific MS signals during bacterial interaction. Two case studies were also investigated: (i) cellobiose-mediated induction for the pathogenicity of Streptomyces scabiei, the causative agent of common scab on root and tuber crops, and (ii) iron-repressed production of siderophores of S. scabiei. This report proposes guidelines for MALDI-MSI data treatment applied in the case of microbiology contexts, with enhanced ion peak annotation in specific culture conditions. The strengths and weaknesses of the methods are discussed.

Technologies of physical and chemical impact on potato planting material

The paper highlights that it is planned to increase the cultivation area of open ground vegetables and potatoes for ensuring the food security. (Research purpose) This study aims to explore methods and technologies for pre-planting treatment of potatoes. (Materials and methods) The research was conducted in the Tula region where Rannee Utro (Early Morning) and Rokko potato varieties were studied under natural infectious conditions. Various fungicides and biological products containing different active ingredients were applied to protect potatoes. Additionally, the study investigated the eff ects oflow-pressure mercury ultraviolet discharge lamps and magnetic field treatments on the biopotential and pH levels of potatoes. (Results and discussion) The study focuses on enhancing potato yields by applying direct magnetic field exposure before planting and investigates the impact of ultraviolet irradiation on tuber growth and productivity. Signifi cant emphasis was placed on the efficacy of chemical and biological agents in preventing potato scab. The findings show that optimal biometric indicators and potato yields were achieved with a magnetic induction of 30 millitesla. Any deviation from this treatment dose results in reduced biometric indicators and yields, which, however, remain hirer than those of the untreated controls. (Conclusions) The application of fungicidal disinfectants effectively curtails the development of common scab, with the highest efficacy achieved using Rovral Aquafl o 500. Post-treatment with ultraviolet radiation at a dose of 120-240 joules per square meter enhances vegetative growth, productivity, and tuber reproduction rates. The most favorable biometric indicators and yields were observed when a magnetic induction treatment dose of 0.23 joule-seconds per kilogram was applied.

Discovery and Biosynthesis of Streptolateritic Acids A-D: Acyclic Pentacarboxylic Acids from Streptomyces sp. FXJ1.172 with Promising Activity against Potato Common Scab.

Potato common scab (PCS) is a widespread plant disease that lacks effective control measures. Using a small molecule elicitor, we activate the production of a novel class of polyketide antibiotics, streptolateritic acids A-D, in Streptomyces sp. FXJ1.172. These compounds show a promising control efficacy against PCS and an unusual acyclic pentacarboxylic acid structure. A gene cluster encoding a type I modular polyketide synthase is identified to be responsible for the biosynthesis of these metabolites. A cytochrome P450 (CYP) and an aldehyde dehydrogenase (ADH) encoded by two genes in the cluster are proposed to catalyze iterative oxidation of the starter-unit-derived methyl group and three of six branching methyl groups to carboxylic acids during chain assembly. Our findings highlight how activation of silent biosynthetic gene clusters can be employed to discover completely new natural product classes able to combat PCS and new types of modular polyketide synthase-based biosynthetic machinery.

Studying the pathogenic Streptomyces strains responsible for causing potato common scab in Iran and assessing the efficacy of native S. fimicarius-ghR and S. rochei-FsG in reducing scab lesion development in both potato and radish hosts in vivo

ABSTRACT Potato common scab an important widespread disease caused by Streptomyces species, usually can diminish the market value of tubers. None of the disease management methods is considered efficient. Non-pathogenic Streptomyces species owing to their source of bioactive compounds can alleviate scab severity and strengthen plant vigour. During our survey, three pathogenic strains with atypical composition of Pathogenicity Island (PAI) marker genes prevented radish seed germination by ≥98% and exhibited coalescing superficial, raised or mild pitted lesions in pot trials. Based on 16S rRNA and rpoB sequencing, Streptomyces sp. (FG1 and AAb) and S. rochei-HGs were identified. Our research findings have led us to identify S. rochei-HGs as a novel scab-causing species of potato. In addition, two beneficial Streptomyces strains obtained from potato rhizosphere and soil, including S. fimicarius-ghR and S. rochei-FsG, inhibited streptomyces sp.-FG1 growth with the inhibition halo ≥30 mm on agar plates, alleviated the lesion severity index and showed the control efficacy of 88.88 ± 6.41% and 83.33 ± 16.94% on potato, respectively under greenhouse conditions. Both of them can produce siderophore, IAA and solubilise phosphate. By measuring the plant growth attributes, the application of ghR and FsG strains in pathogen-infected soil showed enhancement in potato root and shoot length as well as radish compared with the controls. Evaluation of the inhibitory compounds of studied antagonists by chemistry methods is ongoing. The disease suppressiveness of strains and their plant growth induction should also be validated at the field level.

Field Evaluation of Ukrainian Potato Varieties for Resistance to Fungal and Bacterial Pathogens in the Polissya Area of Ukraine

This study aimed to assess the field resistance of Ukrainian potato varieties to fungal and bacterial pathogens under natural infectious conditions in the Polissya area of Ukraine. Field experiments were conducted during 2020-2022 to examine the manifestation and spread of fungal and bacterial diseases on 20 Ukrainian potato varieties across different maturity groups. Varieties were evaluated for resistance to Alternaria blight, Rhizoctonia solani, Common scab (Streptomyces spp.), and Fusarium dry rot using predefined scales. The Ukrainian potato varieties Aria, Khortytsia, Kniahynia, Myroslava, Shchedryk, and Slovianka displayed field resistance to Alternaria blight. The varieties Charunka, Feia, Khortytsia, Okolytsia, and Shchedryk showed field resistance to R. solani. The varieties Aria, Okolytsia, Skarbnytsia, Strumok, and Slovianka were highly resistant to Common scab in field conditions, while Anika, Aria, Charunka, Kimmeria, Letana, Slovianka, Shchedryk, and Tyras exhibited field resistance to Fusarium dry rot. Twelve out of 20 potato varieties displayed field resistance to multiple pathogens with five of them (Aria, Charunka, Khortytsia, Slovianka, and Shchedryk) being resistant to the majority of pathogens under investigation. These varieties hold promise for integration into cropping systems with reduced fungicide usage. Additionally, these varieties can be recommended for inclusion in breeding programs as valuable sources of resistance to these fungal and bacterial pathogens. Future research should focus on elucidating the genetic basis of resistance in these varieties and further exploring the nature of inheritance of the observed resistance from the parental forms, that include the varieties Bellarosa, Beloruskyi 3, Bahriana, Slovianka, Oberih, Lyu, Meve, Kondor, Tyras and Barylchykha, and the hybrids 86.281c12, KE 78.50.53, 77.583/16, and P.88.12-11.

Occurrence of New Pathogenic Species of Streptomyces Causing Common Scab Disease on Potato Tubers in Egypt

Occurrence of New Pathogenic Species of Streptomyces Causing Common Scab Disease on Potato Tubers in Egypt

CRISPR/Cas9 genome editing of potato StDMR6-1 results in plants less affected by different stress conditions.

Potato is the third most important food crop, but cultivation is challenged by numerous diseases and adverse abiotic conditions. To combat diseases, frequent fungicide application is common. Knocking out susceptibility genes by genome editing could be a durable option to increase resistance. DMR6 has been described as a susceptibility gene in several crops, based on data that indicates increased resistance upon interruption of the gene function. In potato, Stdmr6-1 mutants have been described to have increased resistance against the late blight pathogen Phytophthora infestans in controlled conditions. Here, we present field evaluations of CRISPR/Cas9 mutants, in a location with a complex population of P. infestans, during four consecutive years that indicate increased resistance to late blight without any trade-off in terms of yield penalty or tuber quality. Furthermore, studies of potato tubers from the field trials indicated increased resistance to common scab, and the mutant lines exhibit increased resistance to early blight pathogen Alternaria solani in controlled conditions. Early blight and common scab are problematic targets in potato resistance breeding, as resistance genes are very scarce. The described broad-spectrum resistance of Stdmr6-1 mutants may further extend to some abiotic stress conditions. In controlled experiments of either drought simulation or salinity, Stdmr6-1 mutant plants are less affected than the background cultivar. Together, these results demonstrate the prospect of the Stdmr6-1 mutants as a useful tool in future sustainable potato cultivation without any apparent trade-offs.

Biocontrol of common scab in potato cultivation

Biocontrol of common scab in potato cultivation

Complete genome sequence of the Streptomyces bacteriophage Amabiko.

Amabiko is a lytic subcluster BE2 bacteriophage that infects Streptomyces scabiei-a bacterium causing common scab in potatoes. Its 131,414 bp genome has a GC content of 49.5% and contains 245 putative protein-coding genes, 45 tRNAs, and one tmRNA. Amabiko is closely related to Streptomyces bacteriophage MindFlayer (gene content similarity: 86.5%).

Retraction of: Nitrogen sources enhance siderophore-mediated competition for iron between potato common scab and late blight causative agents.

Retraction of: Nitrogen sources enhance siderophore-mediated competition for iron between potato common scab and late blight causative agents.

Potato yield and quality are linked to cover crop and soil microbiome, respectively

Crop-specific cultivation practices including crop rotation, cover cropping, and fertilisation are key measures for sustainable farming, for which soil microorganisms are important components. This study aims at identifying links between agronomic practices, potato yield and quality as well as soil microorganisms. We analysed the roles of cover crops and of the soil prokaryotic, fungal, and protistan communities in a long-term trial, differing in crop rotation, i.e. winter wheat or silage maize as pre-crop, presence and positioning of oil radish within the rotation, and fertilisation, i.e. mineral fertiliser, straw, manure, or slurry. Up to 16% higher yields were observed when oil radish grew directly before potatoes. Losses of potato quality due to infection with Rhizoctonia solani-induced diseases and common scab was 43–63% lower when wheat + oil radish was pre-crop under manure or straw + slurry fertilisation than for maize as pre-crop. This contrast was also reflected by 42% higher fungal abundance and differences in β-diversity of prokaryotes, fungi, and protists. Those amplicon sequence variants, which were found in the treatments with highest potato qualities and differed in their abundances from other treatments, belonged to Firmicutes (2.4% of the sequences) and Mortierellaceae (28%), which both comprise potential antagonists of phytopathogens. Among protists, Lobosa, especially Copromyxa, was 62% more abundant in the high potato quality plots compared to all others, suggesting that specific higher trophic organisms can improve crop performance. Our findings suggest that successful potato cultivation is related (1) to planting of oil radish before potatoes for increasing yield and (2) to fertilisation with manure or straw + slurry for enriching the microbiome with crop-beneficial taxa.

Isolation, characterization and application of noble bacteriophages targeting potato common scab pathogen Streptomyces stelliscabiei

Bacteriophages have emerged as promising alternatives to pesticides for controlling bacterial pathogens in crops. Among these pathogens, Streptomyces stelliscabiei (syn. S. stelliscabiei) is a primary causative agent of potato common scab (PCS), resulting in substantial global economic losses. The traditional management methods for PCS face numerous challenges, highlighting the need for effective and environmentally friendly control strategies. In this study, we successfully isolated three novel bacteriophages, namely Psst1, Psst2, and Psst4, which exhibited a broad host range encompassing seven S. stelliscabiei strains. Morphological analysis revealed their distinct features, including an icosahedral head and a non-contractile tail. These phages demonstrated stability across a broad range of temperatures (20–50°C), pH (pH 3–11), and UV exposure time (80 min). Genome sequencing revealed double-stranded DNA phage with open reading frames encoding genes for phage structure, DNA packaging and replication, host lysis and other essential functions. These phages lacked genes for antibiotic resistance, virulence, and toxicity. Average nucleotide identity, phylogenetic, and comparative genomic analyses classified the three phages as members of the Rimavirus genus, with Psst1 and Psst2 representing novel species. All three phages efficiently lysed S. stelliscabiei in the liquid medium and alleviated scab symptom development and reduced pathogen abundance on potato slices. Furthermore, phage treatments of radish seedlings alleviated the growth inhibition caused by S. stelliscabiei with no disease symptoms. In soil potted experiments, phages significantly reduced disease incidence by 40%. This decrease is attributed to a reduction in pathogen density and the selection of S. stelliscabiei strains with reduced virulence and slower growth rates in natural environments. Our study is the first to report the isolation of three novel phages that infect S. stelliscabiei as a host bacterium. These phages exhibit a broad host range, and demonstrate stability under a variety of environmental conditions. Additionally, they demonstrate biocontrol efficacy against bacterial infections in potato slices, radish seedlings, and potted experiments, underscoring their significant potential as biocontrol agents for the effective management of PCS.

Improvement of an ecologically safe system of control of fungal diseases for growing on the basis of organic farming

Goal. To assess the level of effectiveness of the elements of control of fungal diseases in potato agrocenoses for various combinations of biofungicides with biologically active substances and fertilizers, methods of application and the reaction of potatoes of the Myroslav variety to them, for growing on the basis of organic farming.
 Methods. The following methods were used during the research: field — monitoring of the main diseases of potatoes in field experiments, crop accounting, determination of the effectiveness of combinations of biofungicides with plant growth regulators, organic and organo-mineral fertilizers; laboratory — accounting for damage to tubers by diseases, according to generally accepted methods.
 Results. In 2021—2022, the Laboratory of Immunity and Plant Protection of the Institute of Potato Breeding of the National Academy of Sciences conducted research on improving the elements of an environmentally safe system of controlling fungal diseases for cultivation based on organic farming. The research used the Myroslav variety of the institute’s selection, biopreparations with insecticidal, fungicidal and growth-regulating action, and organic and organo-mineral fertilizers. The lowest level of Alternaria development was noted in option 9 (treatment of tubers — organic fertilizer + PPR + plant treatment Bactophyt + PPR + organic and organo-mineral fertilizer), the development of the disease was 25.0%, the spread was 35.0 %, and the technical efficiency of the elements protection was 56.7%. It was established that for effective control of the development of common scab, rhizoctoniosis and fusarium dry rot, it is advisable to use a mixture of substances (PPR + organic fertilizer — treatment of tubers + biofungicide + organic and organo-mineral fertilizer + PPR — plant treatment), which significantly reduced the level of disease development tubers and limited their spread, compared to control and standards. The yield of potatoes in the variants was higher than in the control (22.5 t/ha) and was in the range of 31.1—42.0 t/ha. The level of the preserved harvest, relative to the control, was in the range of 8.6—19.5 t/ ha. The highest level of yield is 42.0 t/ha, noted in option 9 (organic fertilizer + PPR treatment of tubers + three Bactophyt plant treatments + organic and organo-mineral fertilizer + PPR) which, respectively, is 19.5 t/ha higher than the control and by 3.1 t/ha — standard.
 Conclusions. The use of tank mixtures of biofungicides with growth regulators and fertilizers significantly reduces the level of potato disease development and helps to increase the level of its yield. It has been established that the mixture of drugs (PPR + organic fertilizer — treatment of tubers + biofungicide + organic and organo-mineral fertilizer + PPR — plant treatment) is advisable to use to control the development of alternariosis, common scab, rhizoctoniosis and fusarium dry rot, since such a combination is ecologically safe for the environment, at the same time significantly reduces the level of development of fungal diseases and limits their spread, in comparison with control and standards, for growing on the basis of organic farming.

The Role of Soil Abundance of TxtAB in Potato Common Scab Disease Severity.

Common scab is an economically costly soilborne disease of potato endemic in many potato-growing regions. The disease is caused by species of Streptomyces bacteria that produce the phytotoxin thaxtomin A. The primary disease management tool available to growers is planting resistant cultivars, but no cultivar is fully resistant to common scab, and partially resistant cultivars are often not the preferred choice of growers because of agronomic or market considerations. Therefore, growers would benefit from knowledge of the presence and severity of common scab infestations in field soils to make informed planting decisions. We implemented a quantitative PCR diagnostic assay to enable field detection and quantification of all strains of Streptomyces that cause common scab in the United States through amplification of thaxtomin A biosynthetic genes. Greenhouse trials confirmed that pathogen abundance was highly correlated with disease severity for five distinct phytopathogenic Streptomyces species, although the degree of disease severity was dependent on the pathogen species. Correlations between the abundance of the thaxtomin biosynthetic genes from field soil with disease on tubers at field sites across four U.S. states and across 2 years were not as strong as correlations observed in greenhouse assays. We also developed an effective droplet digital PCR diagnostic assay that also has potential for field quantification of thaxtomin biosynthetic genes. Further improvement of the PCR assays and added modeling of other environmental factors that impact disease outcome, such as soil composition, can aid growers in making informed planting decisions.