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Introduction: 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. Methods: 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. Results: 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. Discussion: 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. [ABSTRACT FROM AUTHOR]

IntroductionThe 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.MethodsIntracellular 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.ResultsPotato 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.DiscussionThese 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.

Due to pathogen resistance as well as the high costs and adverse environmental effects of the use of chemical pesticides, researchers are looking for other ways to control pests and diseases such as biological control. Many studies prove the antibacterial effects of the biochemical compounds of the garlic plant, but there is no report on the antimicrobial activities of the heat-stable protein of the garlic plant. Considering the proven role of these proteins in response to stresses, this study was conducted to investigate the antibacterial role of these proteins on Ralstonia solanacearum and Streptomyces scabies bacteria. The antimicrobial properties of each bacterium were tested in separate experiments using a completely randomized factorial design with three factors and three repeats. Heat-stable protein from Clones, tissues, and various concentrations applied to R. solanacearum bacteria expressed a highly significant difference in the diameter of the inhibition zone and The highest inhibition zone was related to the leaf of Hamadan Clone. The lowest minimum inhibitory concentration MIC and minimal bactericidal concentration MBC were related to the leaf HSP of the Hamadan clone. As a result, Hamadan leaves with smaller MIC and MBC and the larger inhibitory zone in relation to the other treatments showed the highest inhibitory effect. In SDS-PAGE electrophoresis the leaves heat-stable protein electrophoresis banding only the HSP40 family was observed, while, on the garlic cloves families, small HSP (sHSP), HSP40, HSP70, HSP90, and HSP100 were seen. The results indicate that heat-stable protein from garlic could be used as a major antimicrobial agent against pathogenic R. solanacearum bacteria but had no biological role as an antimicrobial on S. scabies bacteria. The results of the present research show that the HSP of garlic plants can be used to create resistance to R. solanacearum bacteria.

Common scab is a disease caused by Streptomyces spp. that can significantly reduce potato crop yield and quality, affecting marketability. Traditionally, pesticides have been used to prevent this disease, but this approach has several drawbacks, including the development of pesticide resistance and negative effects on the environment and human health. Therefore, it was essential to develop eco-friendly Integrated Disease Management (IDM) strategies for common scab management. In this study, we evaluated 13 different treatments in various combinations with three replications each. We found that treatment T2 (soil amendments with gypsum at 2.0 t/ha + tuber treatments with Trichoderma harzianum at 5 g/kg + foliar spray of copper oxychloride with streptocycline in a 3:1 ratio) showed the highest reduction in disease severity (3.63%) and incidence (1.79%) compared to the control (46.60% and 34.57%, respectively). Moreover, IDM practices also altered the physiochemical properties of the soil. T2 treatment resulted in the highest pH value of 5.86 after planting and 5.30 after harvesting, with the minimum Electrical Conductivity (EC) value estimated to be 0.089 S/m after planting and 0.087 S/m after harvesting. After planting, T2 treatment showed a soil content of 2.12 mg/kg zinc, 3.41 mg/kg copper, and 38.83 mg/kg iron, which increased to 2.42 mg/kg zinc, 3.27 mg/kg copper, and 38.39 mg/kg iron after harvesting. T4 treatment (soil amendments with elemental sulphur at 0.5 t/ha + tuber treatments with T. harzianum at 5 g/kg + foliar spray of copper oxychloride with streptocycline in a 3:1 ratio) showed the highest sulphur content, estimated at 47.69 mg/kg after planting and 48.43 mg/kg after harvesting, and reduced the disease severity and incidence by 10.89% and 7.19%, respectively. T3 treatment (MnSO4 at 15 kg/ha + T. harzianum at 5 g/kg + copper oxychloride with streptocycline in a 3:1 ratio) resulted in the highest soil content of manganese, with 96.47 mg/kg after planting and 98.84 mg/kg after harvesting. Overall, T2 treatment showed the most effective control against common scab disease and is recommended as the best IDM strategy for potato common scab management. [ABSTRACT FROM AUTHOR]

Due to pathogen resistance as well as the high costs and adverse environmental effects of the use of chemical pesticides, researchers are looking for other ways to control pests and diseases such as biological control. Many studies prove the antibacterial effects of the biochemical compounds of the garlic plant, but there is no report on the antimicrobial activities of the heat-stable protein of the garlic plant. Considering the proven role of these proteins in response to stresses, this study was conducted to investigate the antibacterial role of these proteins on Ralstonia solanacearum and Streptomyces scabies bacteria. The antimicrobial properties of each bacterium were tested in separate experiments using a completely randomized factorial design with three factors and three repeats. Heat-stable protein from Clones, tissues, and various concentrations applied to R. solanacearum bacteria expressed a highly significant difference in the diameter of the inhibition zone and The highest inhibition zone was related to the leaf of Hamadan Clone. The lowest minimum inhibitory concentration MIC and minimal bactericidal concentration MBC were related to the leaf HSP of the Hamadan clone. As a result, Hamadan leaves with smaller MIC and MBC and the larger inhibitory zone in relation to the other treatments showed the highest inhibitory effect. In SDS-PAGE electrophoresis the leaves heat-stable protein electrophoresis banding only the HSP40 family was observed, while, on the garlic cloves families, small HSP (sHSP), HSP40, HSP70, HSP90, and HSP100 were seen. The results indicate that heat-stable protein from garlic could be used as a major antimicrobial agent against pathogenic R. solanacearum bacteria but had no biological role as an antimicrobial on S. scabies bacteria. The results of the present research show that the HSP of garlic plants can be used to create resistance to R. solanacearum bacteria. [ABSTRACT FROM AUTHOR]

Se realizó el experimento en Itacurubí de la Cordillera, Paraguay, desde julio de 2021a enero de 2022, donde se evaluó el efecto de la aplicación foliar de un extracto de estevia (Stevia rebaudiana Bertoni) y de un bioestimulante comercial formulado con agua y miel conteniendo 4,05x108UFC.mL-1deLactobacillussp.yde Saccharomycessp., y 3,1x109UFC.mL-1de Streptomyces scabies, comparados con un testigo, sobre el rendimiento de sandía variedad Crimson Sweet. Se utilizó el diseño experimental de bloques completamente al azar con cuatro repeticiones. La primera aplicación de los tratamientos se realizó en el semillero, cuando la plántula contenía 8 hojas definitivas, luego del trasplante, se realizó una aplicación cada 8 días hasta completar 10 aplicaciones en total. Se evaluó el peso promedio de los frutos, el número de frutos por planta y el rendimiento. Los datos fueron sometidosa un análisis de varianza (ANAVA), cuando hubo diferencias significativas entre las medias de los tratamientos, se aplicó la prueba de comparación de medias de Tukey al 5% de probabilidad de error. Con el extracto de estevia se obtuvo 1,9 frutos por planta, con peso promedio de 10 kg y rendimiento de 9119 kg.ha-1, mientras que con el bioestimulante comercial se obtuvo 1,6 frutos por planta, con peso promedio de 8,3 kg y rendimiento de 7325 kg.ha-1. Con el testigo se obtuvo 0,9 frutos por planta con 4,6 kg y un rendimiento de 4044 kg.ha-1. El extracto de estevia ofrece una mayor productividad en el cultivo de sandía. Se sugiere la realización de más estudios para evaluar diferentes dosis de los extractos y considerar variables relacionadas a la fitosanidad y a la calidad postcosecha

Potato common scab, caused mainly by Streptomyces scabies, causes surface necrosis and reduces the economic value of potato tubers, but effective chemical control is still lacking. In this study, an attempt was made to control potato common scab by inoculating potatoes with Bacillus velezensis (B. velezensis) and to further investigate the mechanism of biological control. The results showed that B. velezensis Y6 could reduce the disease severity of potato common scab from 49.92 ± 25.74% [inoculated with Streptomyces scabies (S. scabies) only] to 5.56 ± 1.89% (inoculated with S. scabies and Y6 on the same day) and increase the potato yield by 37.32% compared with the control under pot experiment in this study. Moreover, in the field trial, it was found that Y6 could also significantly reduce disease severity from 13.20 ± 1.00% to 4.00 ± 0.70% and increase the potato yield from 2.07 ± 0.10 ton/mu to 2.87 ± 0.28 ton/mu (p

The intensity of scab caused by Streptomyces scabies on mother seed tubers significantly impacts the scab severity in the harvested crop. In the current study, it is revealed that scab severity on infected mother seed tubers and duration of crop directly affects the disease severity in progeny crop. Mother seed tubers with disease severity grade of 0, 1, 2, and 3 were sown with different crop duration periods of 70, 80 and 90 days. Significantly greater disease incidence and severity were recorded when seed tubers of infection grades 2 and 3 were sown (59.41 and 64.26% incidence; 6.7 and 7.2% severity, respectively). Significantly lesser scab incidence and severity were recorded at 70 DAP (35.64 and 2.4%, respectively) than at 80 and 90 DAP. It was also found that the disease incidence in 80 and 90 days old crop from mother seed tuber of infection grade 0 was statistically similar to disease incidence in 70/80/90 days old crop of mother seed tubers with infection grade of 2 and 3. Significantly maximum lesion grade was found in 90 days old crop sown from mother seed with scab severity grade 3. This shows that the scab incidence and severity increases in the crop with increase in the disease severity grades of mother seed tubers and increased duration of crop by delaying the harvesting interval. Hence, the strategy of planting seed tubers with minimum scab severity grade and harvesting the crop earlier, preferably at 70 DAP, can be utilized to lower the disease severity in progeny crop. [ABSTRACT FROM AUTHOR]

Streptomyces scabies is the best‐characterized plant‐pathogenic streptomycete, which is a special species among the large genus Streptomyces. The pathogenicity of S. scabies relies on the production of the secondary metabolite thaxtomin A. Little is known about the molecular mechanisms underlying the regulation of thaxtomin biosynthesis in S. scabies beyond the pathway‐specific activator TxtR and the cellulose utilization repressor CebR. The leucine‐responsive regulatory protein (Lrp) family modulates secondary metabolism in nonpathogenic streptomycetes. However, the regulatory relationship between the Lrp and pathogenic streptomycetes remains unknown. In this study, we demonstrated that SCAB_Lrp (SCAB_77931) from S. scabies significantly affects thaxtomin biosynthesis, pathogenicity, and morphological development. SCAB_Lrp deletion resulted in a dramatic decline in thaxtomin A production and a low‐virulence phenotype of S. scabies. An in‐depth dissection of the regulatory mechanism of SCAB_Lrp revealed that it positively regulates the transcription of the thaxtomin biosynthetic gene cluster by directly binding to the promoter of the cluster‐situated regulator gene txtR. SCAB_Lrp also controls the morphological development of S. scabies by directly activating the transcription of amfC, whiB, and ssgB. SCAB_Lrp directly controls the transcription of its own gene by binding a specific sequence (5′‐GGACAGTCGCCGTGCTACG‐3′). Moreover, phenylalanine and methionine have been characterized as SCAB_Lrp effectors by strengthening the binding affinity and complex status between SCAB_Lrp and DNA. Our findings characterize a multifunctional regulatory protein, SCAB_Lrp, that controls secondary metabolism, pathogenicity, and sporulation in S. scabies and provide new insights into the complex regulatory network that modulates thaxtomin phytotoxins in pathogenic Streptomyces. [ABSTRACT FROM AUTHOR]

Potato common scab (CS) and peanut pod wart diseases cause substantial economic losses every year in Israel. In this comprehensive study on the Streptomyces spp. population, isolates were collected during 2004–2016 from potato tubers with symptoms grown in Israel, seed tubers imported from Europe and from peanut pods with symptoms grown in Israel. A total of 142 isolates were characterized by PCR using three primer sets (txtA, tomA and nec1 genes) and by three pathogenicity tests. Seven species were identified among the isolates, S. bottropensis, S. europaeiscabiei, S. griseus, S. scabiei, S. sampsonii, S. turgidiscabies, and S. venezuelae. S. europaeiscabiei was the most dominant among isolates from imported seed tubers, while S. scabiei and S. turgidiscabies were isolated from tubers grown in Israel. Isolates originating from peanuts were significantly more virulent than those from imported seed tubers, as determined by a pathogenicity assay on radish plants. The presence of pathogenic Streptomyces was detected by quantitative PCR (qPCR) in 289 soil samples collected from 31 commercial potato fields with CS history. Eighty percent to 100% of samples collected from fields with a high disease incidence on tubers (50%) gave positive results in qPCR, whereas in samples collected from fields with low CS incidence (2%–30%) the qPCR results were very variable. Potato seed lots imported from Europe during 2008–2021 were found contaminated with CS symptoms at different levels on visual examination. The results of this study indicate that Streptomyces species, in particular S. europaeiscabiei, were introduced to Israel through seed lots imported from Europe. [ABSTRACT FROM AUTHOR]

Potato common scab, which is mainly caused by the bacterium Streptomyces scabies, occurs in key potato growing regions worldwide. It causes necrotic or corky symptoms on potato tubers and decreases the economic value of potato. At present, there is no recommended chemical or biological control for combating potato common scab in Taiwan. It can only reduce the occurrence by cultivation control, but the efficacy is limited. Previously we found that Bacillus amyloliquefaciens Ba01 could control potato common scab in pot assay and in the field. The potential anti-S. scabies mechanism was associated with surfactin secretion, but further molecular dissection was not conducted. Thus, in this study we aimed to determine whether surfactin is the main compound active against S. scabies by knocking out the srf gene cluster in Ba01. The cloning plasmid pRY1 was transformed to Ba01 by electroporation for in-frame deletion. Two independent Δsrf mutants were obtained and confirmed by specific primers and mass spectrometry. The swarming ability and S. scabies inhibition was significantly decreased (P<0.001) in Δsrf mutants. The swarming ability of Δsrf mutants could be restored by the addition of surfactin. Furthermore, we found that Ba01 formed wrinkled biofilm in MSgg liquid medium, while Δsrf mutants formed biofilm abnormally. Furthermore, the α-amylase, protease and phosphate-solubilizing ability of Δsrf mutants was decreased, and the mutants could not inhibit the growth and sporulation of S. scabies on potato tuber slices. In conclusion, srf gene cluster of B. amyloliquefaciens Ba01 is responsible for the secretion of surfactin and inhibition of S. scabies. [ABSTRACT FROM AUTHOR]

Potato scab is an important soil-borne disease that can significantly reduce the quality and economic value of potatoes. The purpose of this study was to isolate, screen and identify endophytic bacteria that have antagonistic and control effects on potato scab disease, and to determine the control effect and yield traits of the selected strains on potato scab disease in field conditions. A bacterial strain K-9 was isolated from the junction between scab spot and healthy epidermis of potato tuber. The K-9 strain was identified as Bacillus sp. through morphological, physiological and biochemical characterization, and 16S rDNA and gyrB gene sequence analysis. The diameter of the inhibition zone of strain K-9 against Streptomyces scabies on the YME plate was 3.82 cm. The K-9 strain could inhibit eight types of crop pathogens, with the highest inhibition rate (70.39%) against another soil-borne potato disease (potato black scurf). In the field test, the control effect of K-9 strain against potato scab was not significantly different from that of mixed bacteria or chemical agents, but the disease index and the scab index in the K-9 treatment were significantly lower than in the control. The potato yield in the K-9 treatment was 12.44% higher than the control. In summary, the K-9 strain can prevent not only potato scab, but also increase potato yield. Therefore, the endophytic bacterial K-9 strain may be a potential biological control agent. [ABSTRACT FROM AUTHOR]

Potato common scab is a main soil-borne disease of potato that can significantly reduce its quality. At present, it is still a challenge to control potato common scab in the field. To address this problem, the 972 family lactococcin (Lcn972) was screened from Bacillus velezensis HN-Q-8 in this study, and an Escherichia coli overexpression system was used to obtain Lcn972, which showed a significant inhibitory effect on Streptomyces scabies, with a minimum inhibitory concentration of 10.58 µg/mL. The stability test showed that Lcn972 is stable against UV radiation and high temperature. In addition, long-term storage at room temperature and 4°C had limited effects on its activity level. The antibacterial activity of Lcn972 was enhanced by Cu2+ and Ca2+, but decreased by protease K. The protein was completely inactivated by Fe2+. Cell membrane staining showed that Lcn972 damaged the cell membrane integrity of S. scabies. Scanning electron microscope (SEM) and transmission electron microscope (TEM) observations revealed that the hyphae of S. scabies treated with Lcn972 were deformed and adhered, the cell membrane was incomplete, the cytoplasm distribution was uneven, and the cell appeared hollow inside, which led to the death of S. scabies. In conclusion, we used bacteriocin for controlling potato common scab for the first time in this study, and it provides theoretical support for the further application of bacteriocin in the control of plant diseases. [ABSTRACT FROM AUTHOR]

Bactericides Krosin AG and Timsen; fungicides Oxicob, Micra 72WP, Provex 200WP, and Amister Top; and plant nutrients Mag Plus and Alpha Boron Plus were evaluated against Streptomyces scabies in vitro and under field conditions. Among the chemicals, Oxicob (3500 ppm) and Krosin AG (2000 ppm) demonstrated maximum zone of inhibition against S. scabies by 20.61 and 19.74 mm, respectively in in vitro. In field, maximum reduction of common scab incidence by number (64.99%) & weight (66.02%), and severity (73.53%) was achieved by Oxicob. Along with the reduction of common scab incidence by number (49.92%) & weight (47.70%), and severity (49.47%), Alpha Boron Plus resulted the highest potato tuber yield (18.07 ton ha−1) in comparison to other chemicals. The present study suggests that combination of Oxicob and Alpha Boron Plus can be applied in the field to increase potato tuber yield. [ABSTRACT FROM AUTHOR]

Three isolates of Streptomyces scabies (St.1, St.2, and St.3) were examined for virulence on potato mini tubers, necrosis initiation on potato slices, inhibition of radish seedling length, production of thaxtomin A, and the presence of thaxtomin A (txtA) and nec1 genes. The three isolates, St.1, St.2, and St.3, were classified as highly virulent, moderately virulent, and weakly virulent, respectively. The St.1 isolate showed the highest scab severity index on potato mini tubers and necrosis on potato slices, while the St.3 had the lowest, and St.2 had intermediate values. The St.1 reduced radish seedling length by 82.35% and produced the highest toxin level (3.1 mg/ml), while the St.3 isolate reduced seedling length by 63.5% and produced the lowest level of toxin (1.18 mg/ml). The three isolates were positive for the presence of thaxtomin A (txtA) gene and produced a specific gene band at 500bp. However, St.1 and St.2 isolates were able to create a particular band at 700bp associated with the necrosis gene (nec1), while the isolate St.3 lacked this band. Based on the total protein profile analysis, the three S. scabies isolates clustered into two groups which diverged at a similarity index of 0.78. The St.2 and St.3 virulent isolates were located in the same group with 0.86 similarity, while the highly virulent isolate St.1 was located in a separate group. Current findings highlight the correlation between the presence of thaxtomin A and necrosis virulence factors and S. scabies pathogenicity. [ABSTRACT FROM AUTHOR]

The common scab disease caused by Streptomyces scabies , a soil-dwelling Gram-positive bacterium, is an economically important disease of potatoes and other tuber crops. The lack of effective treatments against this disease accounts for large economic losses globally. Plant extracts were screened to find several that effectively inhibited Streptomyces scabies growth in culture. Seven tinctures showed the greatest inhibition of S. scabies growth by reducing pathogen growth in culture by 75% or more. These extracts were myrrh, garlic, cayenne, barberry, frankincense, wild indigo root, and lavender. Myrrh extract from Commiphora myrrha , a resin made from tree sap, showed strong antibacterial activity by reducing the growth of S. scabies to 13% of the control. Additionally, a flavonoid library was screened to identify several compounds that were effective to control the pathogen growth. The flavonoids that showed the greatest inhibition of Streptomyces scabies growth were sophoraflavanone G, jaceosidin, baicalein, and quercetin. Minimum inhibitory concentrations for the effective flavonoids were calculated to be 6.8 ± 0.4 μM, 100.0 ± 2.1 μM, 202.9 ± 5.3 μM, and 285.2 ± 6.8 μM, respectively. The mean lethal doses for these flavonoids against Streptomyces scabies were 2.0 ± 0.1 μM, 22.6 ± 0.5 μM, 52.9 ± 1.3 μM, and 37.8 ± 1.0 μM, respectively. A live/dead assay showed complete cell death in the presence of sophoraflavanone G indicative of a bactericidal mechanism for flavonoid action on Streptomyces scabies. Scanning electron and transmission electron microscopy imaging showed damaged cell membrane morphologies when Streptomyces scabies was exposed to these flavonoids. Mycelia appeared as flat and deflated structures with contents seen as spewing from branching hyphae with numerous holes and tears in the membrane structure indicative of cell death. Sophoraflavanone G showed the greatest potency and potential as a natural antibiotic from the library of tested flavonoids. These results suggest that these plant compounds act on the pathogen through a bactericidal mechanism involving cell membrane destabilization and disruption leading to cell death. [ABSTRACT FROM AUTHOR]

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The common scab disease caused by Streptomyces scabies, a soil-dwelling Gram-positive bacterium, is an economically important disease of potatoes and other tuber crops. The lack of effective treatments against this disease accounts for large economic losses globally. Plant extracts were screened to find several that effectively inhibited Streptomyces scabies growth in culture. Seven tinctures showed the greatest inhibition of S. scabies growth by reducing pathogen growth in culture by 75% or more. These extracts were myrrh, garlic, cayenne, barberry, frankincense, wild indigo root, and lavender. Myrrh extract from Commiphora myrrha, a resin made from tree sap, showed strong antibacterial activity by reducing the growth of S. scabies to 13% of the control. Additionally, a flavonoid library was screened to identify several compounds that were effective to control the pathogen growth. The flavonoids that showed the greatest inhibition of Streptomyces scabies growth were sophoraflavanone G, jaceosidin, baicalein, and quercetin. Minimum inhibitory concentrations for the effective flavonoids were calculated to be 6.8 ± 0.4 μM, 100.0 ± 2.1 μM, 202.9 ± 5.3 μM, and 285.2 ± 6.8 μM, respectively. The mean lethal doses for these flavonoids against Streptomyces scabies were 2.0 ± 0.1 μM, 22.6 ± 0.5 μM, 52.9 ± 1.3 μM, and 37.8 ± 1.0 μM, respectively. A live/dead assay showed complete cell death in the presence of sophoraflavanone G indicative of a bactericidal mechanism for flavonoid action on Streptomyces scabies. Scanning electron and transmission electron microscopy imaging showed damaged cell membrane morphologies when Streptomyces scabies was exposed to these flavonoids. Mycelia appeared as flat and deflated structures with contents seen as spewing from branching hyphae with numerous holes and tears in the membrane structure indicative of cell death. Sophoraflavanone G showed the greatest potency and potential as a natural antibiotic from the library of tested flavonoids. These results suggest that these plant compounds act on the pathogen through a bactericidal mechanism involving cell membrane destabilization and disruption leading to cell death.

Agricultural soil harbors a diverse microbiome that can form beneficial relationships with plants, including the inhibition of plant pathogens. Pseudomonas spp. are one of the most abundant bacterial genera in the soil and rhizosphere and play important roles in promoting plant health. However, the genetic determinants of this beneficial activity are only partially understood. Here, we genetically and phenotypically characterize the Pseudomonas fluorescens population in a commercial potato field, where we identify strong correlations between specialized metabolite biosynthesis and antagonism of the potato pathogens Streptomyces scabies and Phytophthora infestans. Genetic and chemical analyses identified hydrogen cyanide and cyclic lipopeptides as key specialized metabolites associated with S. scabies inhibition, which was supported by in planta biocontrol experiments. We show that a single potato field contains a hugely diverse and dynamic population of Pseudomonas bacteria, whose capacity to produce specialized metabolites is shaped both by plant colonization and defined environmental inputs.

Potato common scab caused by Streptomyces scabies is one of the most economically important diseases infecting potato. It reduces the quality of potato tubers, which subsequently decreases the tuber prices and causes significant economic losses for potato growers. Biological control using bacteriophages is a promising strategy for controlling this disease. In this study, a novel bacteriophage with high lytic efficacy against S. scabies was isolated from a potato field at El-Minya, Egypt, and was designated SscP1EGY. The phage has an icosahedral head of 55 nm and a short tail of 7.5 nm, typical of a podovirus. Its infection cycle was 90 min, including 50 min of latent time and 40 min of rise period with a burst size of approximately 200 PFU per infected cell. The genome of SscP1EGY consists 51,751 nucleotides with 76 predicted genes. SscP1EGY infected and completely lysed seven tested S. scabies strains but showed no lytic activity against three beneficial Streptomyces species, other beneficial bacterial species, and non-target plant pathogenic bacteria. In greenhouse experiments, treatment of S. scabies-inoculated potato tubers with phage SscP1EGY resulted in reductions of (1) the severity of scab, (2) the number of lesions, and (3) the percentage of lesion surface, as compared to the inoculated tubers without phage treatment. Also, scab lesions appeared superficial in phage-treated tubers but pitted in non-phage-treated tubers. Our results suggest that SscP1EGY has a potential as a biological control agent for S. scabies. Based on our knowledge, SscP1EGY is the first sequenced S. scabies-infecting phage in Egypt. [ABSTRACT FROM AUTHOR]

Potato common scab is a soil-borne bacterial disease caused by Streptomyces scabies , which is ubiquitous and difficult to control. In this study, the issue of developing antimicrobial agents derived from plant extracts against S. scabies was addressed. Three bioactive phenolic compounds, named gallic acid, 1-O-galloyl-β- d -glucose, and corilagin, were isolated and identified from Phyllanthus emblica pomace through bioassay-guided fractionation. The antibacterial effects of these compounds on S. scabies were evaluated with MIC values of 0.63, 0.31, and 1.25 mg/mL, respectively. Furthermore, Structure-activity relationship analyses of 17 gallic acid and its structural analogs revealed that the R 6 position of the benzene ring was a key factor to their antibacterial activity against S. scabies , among which pyrogallol had the best antibacterial effect. Scanning electron microscopy showed that when S. scabies was exposed to this gallic acid and its structural analogs, the cell membranes of which was damaged. The results will help promote the development and structural modification of plant-derived bacteriostatic agents. [Display omitted] • Three phenolic compounds were isolated and characterized from Phyllanthus emblica. • The phenolic compounds showed promising antibacterial activity against S. scabies. • SAR study showed carboxyl substituents of gallic acid affected bactericidal activity. • Gallic acid analog pyrogallol showed the strongest bactericidal activity. • Gallic acid and analogs damaged membrane integrity and permeability of S. scabies. [ABSTRACT FROM AUTHOR]

Biofoundries integrate high-throughput software and hardware platforms with synthetic biology approaches to enable the design, execution and analyses of large-scale experiments. The unique and powerful combination of laboratory infrastructure and expertise in molecular biology and automation programming, provide flexible resources for a wide range of workflows and research areas. Here, we demonstrate the applicability of biofoundries to molecular microbiology, describing the development and application of automated workflows to identify the genetic basis of growth inhibition of the plant pathogen Streptomyces scabies by a Pseudomonas strain isolated from a potato field. Combining transposon mutagenesis with automated high-throughput antagonistic assays, the workflow accelerated the screening of 2880 mutants to correlate growth inhibition with a biosynthetic gene cluster within 2 weeks. [ABSTRACT FROM AUTHOR]

Common scab of potato caused by various species in the genus Streptomyces has assumed serious proportions in certain potato‐growing regions of North India. Although it does not have significant effect on tuber yield, it downgrades quality and reduces marketability. Being soil‐borne, this disease is often difficult to manage. Therefore, the present studies were conducted to evaluate different potato‐based crop rotations prevalent in north India as a part of a strategy to manage Streptomyces scabies population in scab sick fields. Our results showed that S. scabies population in soil can be effectively reduced either by keeping the field fallow after potato or by including mungbean or sunhemp as green manure, in a single year cropping sequence over a period of four years. Three crop rotations, viz. fallow–rice–potato, mungbean–rice–potato and sunhemp–rice–potato, showed maximum decrease in the population of S. scabies in soil resulting in reduced scab severity. The mungbean‐ and sunhemp‐based crop rotations also enhanced rhizospheric soil microflora especially fluorescent pseudomonads and Trichoderma spp. [ABSTRACT FROM AUTHOR]

Potato common scab (PCS) is an economically important disease worldwide. In this study we demonstrated the possible role of Streptomyces violaceusniger AC12AB in controlling PCS. Isolates of Streptomyces scabies were obtained from CS infected tubers collected from Maine United States, which were confirmed by morphological and molecular analysis including 16S rRNA sequencing and RFLP analysis of amplified 16S-23S ITS. Pathogenicity assays related genes including txtAB, nec1, and tomA were also identified in all S. scabies strains through PCR reaction. An antagonistic bacterial strain was isolated from soil in Punjab and identified as S. violaceusniger AC12AB based on 16S rRNA sequencing analysis. Methanolic extract of S. violaceusniger AC12AB contained azalomycin RS-22A which was confirmed by 1H and 13C-NMR, 1H/1H-COSY, HMBC and HMQC techniques. S. violaceusniger AC12AB exhibited plant growth promotion attributes including Indole-3-acetic acid production with 17 μgmL-1 titers, siderophores production, nitrogen fixation and phosphates solubilization potential. When tubers were inoculated with S. violaceusniger AC12AB, significant (P < 0.05) PCS disease reduction up to 90% was observed in greenhouse and field trials, respectively. Likewise, S. violaceusniger AC12AB significantly (P < 0.05) increased potato crop up to 26.8% in field trial. Therefore, plant growth promoting S. violaceusniger AC12AB could provide a dual benefit by decreasing PCS disease severity and increasing potato yield as an effective and inexpensive alternative strategy to manage this disease.

Potato common scab, caused mainly by Streptomyces scabies , causes surface necrosis and reduces the economic value of potato tubers, but effective chemical control is still lacking. In this study, an attempt was made to control potato common scab by inoculating potatoes with Bacillus velezensis ( B. velezensis ) and to further investigate the mechanism of biological control. The results showed that B. velezensis Y6 could reduce the disease severity of potato common scab from 49.92 ± 25.74% [inoculated with Streptomyces scabies ( S. scabies ) only] to 5.56 ± 1.89% (inoculated with S. scabies and Y6 on the same day) and increase the potato yield by 37.32% compared with the control under pot experiment in this study. Moreover, in the field trial, it was found that Y6 could also significantly reduce disease severity from 13.20 ± 1.00% to 4.00 ± 0.70% and increase the potato yield from 2.07 ± 0.10 ton/mu to 2.87 ± 0.28 ton/mu ( p  < 0.01; Tukey's test). Furthermore, RNA-seq analysis indicated that 256 potato genes were upregulated and 183 potato genes were downregulated in response to B. velezensis Y6 inoculation. In addition, strain Y6 was found to induce the expression of plant growth-related genes in potato, including cell wall organization, biogenesis, brassinosteroid biosynthesis, and plant hormone transduction genes, by 1.01-4.29 times. As well as up-regulate hydroquinone metabolism-related genes and several transcription factors (bHLH, MYB, and NAC) by 1.13-4.21 times. In summary, our study will help to understand the molecular mechanism of biological control of potato common scab and improve potato yield., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Tao, Wang, Li, Li, Cai, Zhao, Wang, Zeng, Qin, Xiong and Cai.)

Potato common scab, caused by Streptomyces spp., is one of the leading causes of heavy commercial losses in the potato industry and is thus one of the most serious plant diseases worldwide. This study identified and assessed potential biocontrol agents against potato common scab. In total, 110 isolates were obtained through antagonistic tests; among which, Bacillus sp. strain AMCC 101304 was found to be most effective at inhibiting the potato common scab pathogen, Streptomyces scabies. Bacillus sp. strain AMCC 101304 was finally identified as Bacillus altitudinis by morphological observation, physiological and biochemical experimentation, as well as 16S rRNA sequencing and phylogenetic analysis. Pot experiments were conducted twice (in spring and autumn) to verify the biocontrol effect of B. altitudinis AMCC 101304 against potato common scab. In spring, the control efficiency reached 76.34%. In autumn, the disease incidence was reduced from 100% to 34.19% (one treatment with strain AMCC 101304) and 38.42% (two treatments with strain AMCC 101304), and the control efficiency reached 82.50% (one application) and 78.43% (two applications). The present study demonstrated the potential of an isolate, identified as B. altitudinis AMCC 101304, as an effective biocontrol agent for future use in the field. [ABSTRACT FROM AUTHOR]

Summary: Streptomyces scabies causes potato common scab disease, which reduces the quality and market value of affected tubers. The predominant pathogenicity determinant produced by S. scabies is the thaxtomin A phytotoxin, which is essential for common scab disease development. Production of thaxtomin A involves the nonribosomal peptide synthetases (NRPSs) TxtA and TxtB, both of which contain an adenylation (A‐) domain for selecting and activating the appropriate amino acid during thaxtomin biosynthesis. The genome of S. scabies 87.22 contains three small MbtH‐like protein (MLP)‐coding genes, one of which (txtH) is present in the thaxtomin biosynthesis gene cluster. MLP family members are typically required for the proper folding of NRPS A‐domains and/or stimulating their activities. This study investigated the importance of TxtH during thaxtomin biosynthesis in S. scabies. Biochemical studies showed that TxtH is required for promoting the soluble expression of both the TxtA and TxtB A‐domains in Escherichia coli, and amino acid residues essential for this activity were identified. Deletion of txtH in S. scabies significantly reduced thaxtomin A production, and deletion of one of the two additional MLP homologues in S. scabies completely abolished production. Engineered expression of all three S. scabies MLPs could restore thaxtomin A production in a triple MLP‐deficient strain, while engineered expression of MLPs from other Streptomyces spp. could not. Furthermore, the constructed MLP mutants were reduced in virulence compared to wild‐type S. scabies. The results of our study confirm that TxtH plays a key role in thaxtomin A biosynthesis and plant pathogenicity in S. scabies. [ABSTRACT FROM AUTHOR]

Wild potato relatives are important sources of novel genes useful for potato improvement. Since most wild potato species are diploid and most cultivars are tetraploid, it is typically necessary to employ ploidy manipulations to access wild potato germplasm. A common strategy is unilateral sexual polyploidization (USP), in which a tetraploid cultivated clone is crossed with a diploid that produces 2n gametes. The diploid parent may be a wild plant selected for a trait of interest. Alternatively, the wild plant may be crossed to a cultivated diploid and, after selection, the diploid hybrid is then crossed to the tetraploid parent. This study was designed to compare these two strategies for the introgression of common scab resistance from wild diploid Solanum chacoense (chc) into cultivated potato. Progeny were evaluated in naturally scab-infested soil in Maine and Michigan. There were no differences between introgression methods for tuber surface area covered by scab. Scab lesions were significantly more severe when a hybrid was used as the diploid parent, but this difference is likely not large enough to be important in a breeding program. Reciprocal cross differences were not significant. However, location x clone interactions were detected for both surface area and lesion type. This study revealed that, while hybridization strategy did not play a major role in developing this scab resistant germplasm, it is critical to consider production environment when screening for resistance. [ABSTRACT FROM AUTHOR]

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Streptomyces scabies is a Gram-positive bacterial pathogen that causes common scab disease to several crops, particularly in the potato. It is a soil borne pathogen, a very devastating scab pathogen and difficult to manage in the field. Streptomyces has several species that cause common scab such as S. scabiei, S. acidiscabies, S. europaeiscabiei, S. luridiscabiei, S. niveiscabiei, S. puniciscabiei, S. reticuliscabiei, S. stelliscabiei, S. turgidiscabies, S. ipomoeae. Common scab disease harmfully affects potato economic and market value due to the presence of black spots on the tuber. Owing to its genetic diversity and pathogenicity, the determination of pathogen presence in potato fields is still challenging. In this study, S. scabies genetic diversity was measured by surveying five potato-growing areas of Pakistan during the growing season 2019. A total of 50 Streptomyces isolates, including S. scabies, S. acidiscabies, S. griseoflavus were isolated and identified based on morphologic, biochemical and molecular analysis. Virulent confirmation assays confirmed ten virulent strains of Streptomyces spp. On the potato cultivars Cardinal and Santee. Among the Streptomyces species, S. scabies showed the highest scab index, followed by S. acidiscabies and S. griseoflavus by exhibiting the scab-like lesions on potato tubers. Ten potato cultivars were screened against these virulent isolates of Streptomyces. The Faisalabad white variety showed the highest scab index followed By Cardinal, Tourag, Kuroda, Santee, Lady Rosetta, Asterix, Diamant, Faisalabad red and Sadaf. Moreover, genetic diversity and pathogenicity of Streptomyces spp. on potato tubers were also likely diverse in different geographical regions and also potato cultivars. This study represents a contribution to understanding the local interaction between potatoes and Streptomyces spp. in Pakistan. It will aid in supporting a solution for the management of this pathogen around the world.

Potato is prone to many drastic diseases like potato common scab (CS). As no highly effective methods exist for managing CS, this study explored the possibility of using biological control. Ten bacterial strains were isolated from CS-infected potato tubers from four different locations of Punjab, Pakistan, and identified based on biochemical and molecular analysis. Analysis of 16s rDNA sequences amplified by PCR revealed the isolated bacterial strains to be Streptomyces scabies, S. turgidiscabies and S. stelliscabiei. Pathogenic islands were also confirmed among the isolates after identification of txtAB, nec1, and tomA genes with PCR amplification. One strain isolated from soil was antagonistic to the pathogenic Streptomyces spp., and determined to be Streptomyces A1RT on the basis of 16s rRNA sequencing. A methanolic extract of Streptomyces A1RT contained Isatropolone C, which was purified and structurally determined by 1H- and 13C-NMR, 1H/1H-COSY, HMQC, and HMBC techniques. Streptomyces A1RT also produced the plant growth hormone indole-3-acetic acid (IAA) with a titer of 26 μg ml-1 as confirmed by spectrophotometry and HPLC. In a greenhouse assay, disease severity index was established from 0 to 500. Average disease severity indexes were recorded as 63, 130.5, and 78 for Streptomyces scabies, S. turgidiscabies and S. stelliscabiei, respectively. When Streptomyces A1RT was applied in soil that contained one of these pathogenic isolates, the average disease severity indexes were significantly (P < 0.05) reduced to 11.1, 5.6 and 8.4, respectively. A significant increase in tuber weight and shoot development was also observed with the tubers treated with Streptomyces A1RT. The use of the plant growth-promoting Streptomyces A1RT against potato CS thus provides an alternative strategy to control the disease without affecting environmental, plants, animals and human health.

Abstract: The biosynthesis of phytotoxin thaxtomin A (TXT) constitutes the major pathogenicity determinant in Streptomyces scabies, the most widely studied phytopathogen causing scab disease in potato and other root crops. It is recognized that S. scabies regulates its pathogenicity via γ‐butyrolactone (GBL)‐dependent quorum sensing (QS) signalling. AttM, from Agrobacterium tumefaciens C58 strain, has recently been proposed to have GBL‐assimilative capacity. Here, we presented the introduction of A. tumefaciens‐derived attM gene into S. scabies using the Escherichia coli–Streptomyces shuttle vector pIJ8600 via intergeneric conjugation, followed by the investigation of secondary metabolism (mycelium growth, TXT production and pathogenicity) in S. scabies attM exconjugants (S.s/attM) in comparison with their wild‐type parent strain (S.s/WT). Among the resultant S.s/attM exconjugants, attM was found to be integrated into S. scabies chromosome as analysed by Southern blotting. Moreover, S.s/attM failed to evoke the disease symptoms in planta and displayed altered morphological differentiation in contrast to S.s/WT. The abolishment of TXT production in S.s/attM substantiated the loss of pathogenicity and also implied that attM, when constitutively expressed in S. scabies, could paralyse its GBL signalling pathway. Altogether, lactonase‐coding gene attM would be useful in a quorum quenching strategy for plant protection via suppressing TXT production and pathogenicity of S. scabies. Significance and Impact of the Study: This study provides an efficient means to introduce the lactonase gene attM from Agrobacterium tumefaciens into Streptomyces scabies for evaluating the role of γ–butyrolactone (GBL) in thaxtomin A production and pathogenicity, etc. Our results showed that pathogenicity was abrogated in attM—expressing S. scabies exconjugants. Although there are gene knockout approaches to inactivating GBL signalling and thus pathogenicity in S. scabies, they are not only time consuming due to refractory host but also possibly incomplete in view of gene redundancy. Our work is the first report for a kind of lactonase affecting pathogenicity and/or virulence of scab‐causing Streptomyces species. [ABSTRACT FROM AUTHOR]

Abstract: Thaxtomins are diketopiperazine phytotoxins produced by Streptomyces scabies and other actinobacterial plant pathogens that inhibit cellulose biosynthesis in plants. Due to their potent bioactivity and novel mode of action there has been considerable interest in developing thaxtomins as herbicides for crop protection. To address the need for more stable derivatives, we have developed a new approach for structural diversification of thaxtomins. Genes encoding the thaxtomin NRPS from S. scabies, along with genes encoding a promiscuous tryptophan synthase (TrpS) from Salmonella typhimurium, were assembled in a heterologous host Streptomyces albus. Upon feeding indole derivatives to the engineered S. albus strain, tryptophan intermediates with alternative substituents are biosynthesized and incorporated by the NRPS to deliver a series of thaxtomins with different functionalities in place of the nitro group. The approach described herein, demonstrates how genes from different pathways and different bacterial origins can be combined in a heterologous host to create a de novo biosynthetic pathway to “non‐natural” product target compounds. [ABSTRACT FROM AUTHOR]

Summary: Common scab disease on root and tuber plants is caused by Streptomyces scabies and related species which use the cellulose synthase inhibitor thaxtomin A as the main phytotoxin. Thaxtomin production is primarily triggered by the import of cello‐oligosaccharides. Once inside the cell, the fate of the cello‐oligosaccharides is dichotomized: (i) the fuelling of glycolysis with glucose for the saprophytic lifestyle through the action of β‐glucosidase(s) (BGs); and (ii) elicitation of the pathogenic lifestyle by the inhibition of CebR‐mediated transcriptional repression of thaxtomin biosynthetic genes. Here, we investigated the role of scab57721, encoding a putative BG (BglC), in the onset of the pathogenicity of S. scabies. Enzymatic assays showed that BglC was able to release glucose from cellobiose, cellotriose and all other cello‐oligosaccharides tested. Its inactivation resulted in a phenotype opposite to that expected, as reduced production of thaxtomin was monitored when the mutant was cultivated on medium containing cello‐oligosaccharides as unique carbon source. This unexpected phenotype could be attributed to the highly increased activity of alternative intracellular BGs, probably as a compensation for bglC inactivation, which then prevented cellobiose and cellotriose accumulation to reduce the activity of CebR. In contrast, when the bglC null mutant was cultivated on medium devoid of cello‐oligosaccharides, it instead constitutively produced thaxtomin. This observed hypervirulent phenotype does not fit with the proposed model of the cello‐oligosaccharide‐mediated induction of thaxtomin production, and suggests that the role of BglC in the route to the pathogenic lifestyle of S. scabies is more complex than currently presented. [ABSTRACT FROM AUTHOR]

Potato is prone to many drastic diseases like potato common scab (CS). As no highly effective methods exist for managing CS, this study explored the possibility of using biological control. Ten bacterial strains were isolated from CS-infected potato tubers from four different locations of Punjab, Pakistan, and identified based on biochemical and molecular analysis. Analysis of 16s rDNA sequences amplified by PCR revealed the isolated bacterial strains to be Streptomyces scabies, S. turgidiscabies and S. stelliscabiei. Pathogenic islands were also confirmed among the isolates after identification of txtAB, nec1, and tomA genes with PCR amplification. One strain isolated from soil was antagonistic to the pathogenic Streptomyces spp., and determined to be Streptomyces A1RT on the basis of 16s rRNA sequencing. A methanolic extract of Streptomyces A1RT contained Isatropolone C, which was purified and structurally determined by ¹H- and 13C-NMR, ¹H/¹H-COSY, HMQC, and HMBC techniques. Streptomyces A1RT also produced the plant growth hormone indole-3-acetic acid (IAA) with a titer of 26 µg ml-1 as confirmed by spectrophotometry and HPLC. In a greenhouse assay, disease severity index was established from 0 to 500. Average disease severity indexes were recorded as 63, 130.5, and 78 for Streptomyces scabies, S. turgidiscabies and S. stelliscabiei, respectively. When Streptomyces A1RT was applied in soil that contained one of these pathogenic isolates, the average disease severity indexes were significantly (P < 0.05) reduced to 11.1, 5.6 and 8.4, respectively. A significant increase in tuber weight and shoot development was also observed with the tubers treated with Streptomyces A1RT. The use of the plant growth-promoting Streptomyces A1RT against potato CS thus provides an alternative strategy to control the disease without affecting environmental, plants, animals and human health. [ABSTRACT FROM AUTHOR]

The purpose of the three-year-long field experiment was to identify the effect of the UGmax soil fertilizer (microbiological preparation) on the presence of Streptomyces scabies on tubers of two edible potato cultivars. The experiment was established using the randomized split-block method, in three replications, in central Poland (52°03'N; 22°3'E), on the soil consisting of loamy sands, slightly acidic and acidic. The examined factors included: 1st factor: edible potato cultivars (Satina and Typhoon), 2nd factor: doses and dates of application of the UGmax soil fertilizer (1. control object without UGmax; 2. UGmax applied to soil before planting tubers at a dose of 1.0 dm³·ha-1; 3. UGmax applied to soil before planting tubers at a dose of 0.5 dm³·ha-1, when the height of plants is about 10-15 cm, and in the flower buds making phase at a dose of 0.25 dm³·ha-1; 4. UGmax before planting tubers at a dose of 1.0 dm³·ha-1 and when the height of plants is about 10-15 cm, and in the flower buds making phase at a dose of 0.5 dm³·ha-1; 5. UGmax when the height of plants is about 10-15 cm, and in the flower buds making phase at a dose of 0.5 dm³·ha-1). Symptoms of common scab were assessed on a 9-point scale on 100 tubers randomly collected from different experiment objects. As a result of the study, it was demonstrated that treatments with the use of the UGmax soil fertilizer limited the occurrence of common scab on potato tubers and affected the average level of infestation of the sample and the average level of infestation of infested tubers. [ABSTRACT FROM AUTHOR]

Common scab (CS), caused primarily by the filamentous, soilborne bacterium Streptomyces scabies, creates significant challenges in the production of quality potato tubers in global growing regions. Over the past several decades, numerous studies been conducted to improve our understanding of the impact of cultural and pesticide treatments for managing the health of progeny daughter tubers. None of the previous studies, however, have addressed differences between the impacts of CS from whole seed vs. cut seed pieces on resulting disease on daughter tubers. A greenhouse trial was conducted during 2013-2014 to assess the impact of seed type and CS severity on plant health and CS on daughter tubers. Cut and suberized ‘Snowden’ seed pieces (~2 oz.) exhibiting 0, 5, and ≥50% CS severity were sown in 3-gal pots containing a 50:50 mix of sterilized sand and field soil. Whole ‘Snowden’ seed tubers (~2 oz.) with the same three levels of CS severity were sown under the same conditions. At harvest, approximately 20% of daughter tubers from asymptomatic seed pieces (both cut and whole) exhibited symptoms of CS. Disease incidence and severity significantly increased for pieces that had 5 and ≥50% CS across both experiments. Plants grown from whole seed had significantly higher yield, on average, when compared to cut seed. Daughter tubers produced from whole seed resulted in higher CS incidence than those from cut seed in one of our two experimental trials. Our results indicated a clear advantage to plant common scab-free seed potatoes with the aim of producing healthier daughter tubers. [ABSTRACT FROM AUTHOR]

Common scab caused by the soil-borne bacterium Streptomyces scabies is a serious disease for the potato industry. We have identified a strong source of resistance in the diploid wild relative Solanum chacoense. This resistance has been introgressed into tetraploid cultivated potato via unilateral sexual polyploidization. This paper describes three hybrid clones (M8, M16, M17) for use by potato breeding programs to enhance resistance to common scab. They were created by crossing a diploid clone (50% S. tuberosum, 50% S. chacoense) to tetraploid cultivars, producing hybrids with 75% cultivated and 25% wild germplasm. The clones are male and female fertile, and are adapted to temperate zone production environments. [ABSTRACT FROM AUTHOR]

Scabin is a mono-ADP-ribosyltransferase enzyme and is a putative virulence factor produced by the plant pathogen, Streptomyces scabies. Previously, crystal structures of Scabin were solved in the presence and absence of substrate analogues and inhibitors. Herein, experimental (hydrogen-deuterium exchange), simulated (molecular dynamics), and theoretical (Gaussian Network Modeling) approaches were systematically applied to study the dynamics of apo-Scabin in the context of a Scabin·NAD+·DNA model. MD simulations revealed that the apo-Scabin solution conformation correlates well with the X-ray crystal structure, beyond the conformation of the exposed, mobile regions. In turn, the MD fluctuations correspond with the crystallographic B-factors, with the fluctuations derived from a Gaussian network model, and with the experimental H/D exchange rates. An Essential Dynamics Analysis identified the dynamic aspects of the toxin as a crab-claw-like mechanism of two topological domains, along with coupled deformations of exposed motifs. The “crab-claw” movement resembles the motion of C3-like toxins and emerges as a property of the central β scaffold of catalytic single domain toxins. The exposure and high mobility of the cis side motifs in the Scabin β-core suggest involvement in DNA substrate binding. A ternary Scabin·NAD+·DNA model was produced via an independent docking methodology, where the intermolecular interactions correspond to the region of high mobility identified by dynamics analyses and agree with binding and kinetic data reported for wild-type and Scabin variants. Based on data for the Pierisin-like toxin group, the sequence motif Rβ1–RLa–NLc–STTβ2–WPN–WARTT–(QxE)ARTT emerges as a catalytic signature involved in the enzymatic activity of these DNA-acting toxins. However, these results also show that Scabin possesses a unique DNA-binding motif within the Pierisin-like toxin group. [ABSTRACT FROM AUTHOR]

Scabin was previously identified as a novel DNA-targeting mono-ADP-ribosyltransferase (mART) toxin from the plant pathogen 87.22 strain of Streptomyces scabies. Scabin is a member of the Pierisin-like subgroup of mART toxins, since it targets DNA. An in-depth characterization of both the glycohydrolase and transferase enzymatic activities of Scabin was conducted. Several protein variants were developed based on an initial Scabin?DNA molecular model. Consequently, three residues were deemed important for DNA-binding and transferase activity. Trp128 and Trp155 are important for binding the DNA substrate and participate in the reaction mechanism, whereas Tyr129 was shown to be important only for DNA binding, but was not involved in the reaction mechanism. Trp128 and Trp155 are both conserved within the Pierisin-like toxins, whereas Tyr129 is a unique substitution within the group. Scabin showed substrate specificity toward double-stranded DNA containing a single-base overhang, as a model for single-stranded nicked DNA. The crystal structure of Scabin bound to NADH -- a competitive inhibitor of Scabin -- was determined, providing important insights into the active-site structure and Michaelis-Menten complex of the enzyme. Based on these results, a novel DNA-binding motif is proposed for Scabin with substrate and the key residues that may participate in the Scabin?NAD(+) complex are highlighted. [ABSTRACT FROM AUTHOR]

Coronafacoyl phytotoxins are an important family of plant toxins that are produced by several different phytopathogenic bacteria, including the gammaproteobacterium Pseudomonas syringae and the actinobacterium Streptomyces scabiei (formerly Streptomyces scabies). The phytotoxins consist of coronafacic acid (CFA) linked via an amide bond to different amino acids or amino acid derivatives. Previous work suggested that S. scabiei and P. syringae use distinct biosynthetic pathways for producing CFA, which is subsequently linked to its amino acid partner to form the complete phytotoxin. Here, we provide further evidence that the S. scabiei CFA biosynthetic pathway is novel by characterizing the role of CYP107AK1, a predicted cytochrome P450 that has no homologue in P. syringae. Deletion of the CYP107AK1 gene abolished production of coronafacoyl-isoleucine (CFA-Ile), the primary coronafacoyl phytotoxin produced by S. scabiei. Structural elucidation of accumulated biosynthetic intermediates in the ΔCYP107AK1 mutant indicated that CYP107AK1 is required for introducing the oxygen atom that ultimately forms the carbonyl group in the CFA backbone. The CYP107AK1 gene along with two additional genes involved in CFA-Ile biosynthesis in S. scabiei were found to be associated with putative CFA biosynthetic genes in other actinobacteria but not in other organisms. Analysis of the overall genetic content and organization of known and putative CFA biosynthetic gene clusters, together with phylogenetic analysis of the core biosynthetic genes, indicates that horizontal gene transfer has played an important role in the dissemination of the gene cluster and that rearrangement, insertion, and/or deletion events have likely contributed to the divergent biosynthetic evolution of coronafacoyl phytotoxins in bacteria. [ABSTRACT FROM AUTHOR]

Streptomyces scabies is a common soil bacterium that causes scab symptoms in potatoes. Strong evidence indicates horizontal gene transfer (HGT) among bacteria has influenced the evolution of this plant pathogen and other Streptomyces spp. To extend the study of the HGT to the Streptomyces genus, we explored the effects of the inter-domain HGT in the S. scabies genome. We employed a semi-automatic pipeline based on BLASTp searches and phylogenetic reconstruction. The data show low impact of inter-domain HGT in the S. scabies genome; however, we found a putative plant pathogenesis related 1 (PR1) sequence in the genome of S. scabies and other species of the genus. It is possible that this gene could be used by S. scabies to out-compete other soil organisms. [ABSTRACT FROM AUTHOR]