Potato Common Scab Research Articles

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.

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.

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.

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.

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.

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.

Physiological Functions of the Cello-Oligosaccharides Binding CebE in the Pathogenic Streptomyces sp. AMCC400023.

Potato common scab, an economically important disease worldwide, is caused by pathogenic Streptomyces strains mainly through the effects of thaxtomin. The cello-oligosaccharides binding protein CebE is proposed as a gateway to the pathogenic development of Streptomyces scabiei. In this study, two functional CebE encoding genes, GEO5601 and GEO7671, were identified in pathogenic Streptomyces sp. AMCC400023. With a higher binding affinity towards signal molecules, the deletion of GEO5601 severely impaired thaxtomin-producing capacity and reduced the strain's pathogenicity. Transcriptional analysis confirmed that CebE5601 is also responsible for the import and provision of carbon sources for cell growth. With lower binding affinity, the pathogenicity island (PAI)-localized CebE7671 may assume a new function of mediating the biological process of sporulation, given the significantly impaired formation of ΔGEO7671 spores. The mechanisms of action of CebE proteins unraveled in Streptomyces sp. AMCC400023 will help pave the way for more effective prevention of the potato common scab disease.

Genome Sequence Resource of Streptomyces scabiei LBUM848, a Model Strain Causing Common Scab of Potato

Potato common scab is a deleterious bacterial disease caused by multiple Streptomyces species. In this paper, we report the high-quality genome sequence of the scab-causing strain Streptomyces scabiei LBUM848, which was isolated from a scab-infected potato tuber harvested in Bloomfield (New Brunswick, Canada). LBUM848 has been used as a model strain for more than a decade in our laboratory to study the interaction between plant-beneficial phenazine-producing Pseudomonas spp. and scab-causing Streptomyces spp. The analysis of LBUM848’s genome revealed that this strain harbors an extensive repertoire of virulence determinants, including various phytotoxins and secreted proteins. By comparing the genome of LBUM848 with the genomes of other sequenced S. scabiei strains, we found that LBUM848 is closely related to several scab-causing strains isolated from Prince Edward Island, Canada. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

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

How do pathogens affecting the same host interact with each other? We evaluated here the types of microbe-microbe interactions taking place between Streptomyces scabiei and Phytophthora infestans, the causative agents of common scab and late blight diseases in potato crops, respectively. Under most laboratory culture conditions tested, S. scabiei impaired or completely inhibited the growth of P. infestans by producing either soluble and/or volatile compounds. Increasing peptone levels correlated with increased inhibition of P. infestans. 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 the inhibition of the oomycete growth. Mass spectrometry imaging further uncovered that the zones of secreted siderophores and of P. infestans growth inhibition coincided. Moreover, either the repression of siderophore production or the neutralization of their iron-chelating activity led to a resumption of P. infestans growth. Replacement of peptone by natural nitrogen sources such as ammonium nitrate, sodium nitrate, ammonium sulfate, and urea also triggered siderophore production in S. scabiei. Interestingly, nitrogen source-induced siderophore production also inhibited the growth of Alternaria solani, the causative agent of the potato early blight. Overall, our work further emphasizes the importance of competition for iron between microorganisms that colonize the same niche. As common scab never alters the vegetative propagation of tubers, we propose that S. scabiei, under certain conditions, could play a protective role for its hosts against much more destructive pathogens through exploitative iron competition and volatile compound production.

Seasonal Dynamics of Various Scab-Causing Streptomyces Genotypes Among Potato Fields on Prince Edward Island.

Potato common scab is an important bacterial plant disease caused by numerous Streptomyces species and strains. A better understanding of the genetic diversity and population dynamics of these microorganisms in the field is crucial to develop effective control methods. Our research group previously studied the genetic diversity of scab-causing Streptomyces spp. in Prince Edward Island, one of Canada's most important potato-growing provinces. Fourteen distinct Streptomyces genotypes were identified and displayed contrasting aggressiveness toward potato tubers. To better understand the distribution and occurrence of these genotypes over time under field conditions, the population dynamics were studied in nine commercial potato fields throughout a growing season. A comparative genomic-driven approach was used to design genotype-specific primers and probes, allowing us to quantify, using quantitative polymerase chain reaction, the abundance of each of the 14 genotypes in field soil. Thirteen of the previously identified genotypes were detected in at least one soil sample, with various frequencies and population sizes across the different fields under study. Interestingly, weakly virulent genotypes dominated, independent of time or location. Among them, three genotypes accounted for more than 80% of the genotypes' combined population. Although the highly virulent genotypes were detected in lower relative abundance than the weakly virulent ones, an increase in the highly virulent genotypes' population size was observed over the growing season in most fields. The results will ultimately be useful for the development of targeted common scab control strategies.

Biological control of potato common scab and growth promotion of potato by Bacillus velezensis Y6.

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.

First Report of Streptomyces niveiscabiei Causing Potato Common Scab in Shanxi and Gansu, China.

Multiple species of Streptomyces cause common scab disease in potato (Solanum tuberosum) (Kämpfer et al. 1991). Potato tubers (cv. Jinshu1 #5 and Longshu #6) with severe pitted common scab symptoms were observed from two farms in Chaozhou in Shanxi Province and in Tianzhu in Gansu Province during the national disease survey of bacterial diseases of potatoes in 2021. The disease incidence was around 30% on the 6.7 ha of the Chaozhou farm and 10% on the 0.7 ha on the Tianzhu farm. Three tubers with scab symptoms were surface disinfested with 3% sodium hypochlorite for 1 min. The symptomatic tissue was then ground in sterile water. Serially diluted ground samples were cultured on Streptomyces ISP Medium 5 agar plates (Shirling and Gottlieb 1966) and incubated at 280C for 5 days. Eight pure Streptomyces colonies were obtained and sequenced for identification using the universal 16S rRNA gene primers 27F (5'-AGAGTTTGATCMTGGCTCAG-3') and 1492R (5'-TACGGYTACCTTGTTACGACTT-3') (Monciardini et al. 2002) by colony PCR. Blast results of the sequences against the NCBI GenBank for the eight isolates, ZRIMU1508, ZRIMU1510, ZRIMU1511, ZRIMU1512, ZRIMU1514, ZRIMU1515, ZRIMU1516 and ZRIMU1530 (Accession numbers: OP941573 - OP941580), showed more than 99% sequence identity to S. niveiscabiei NRRLB-24457T type strain. Additionally, 12 housekeeping gene sequences, acnA (OP997624 - OP997625), atpD (OP997622 - OP997623), dnaN (OP997620 - OP997621), gap (OP997618 - OP997619), gyrA (OP997614 - OP997615), gyrB (OP997612 - OP997613), infB (OP997610- OP997611), mdh (OP997608 - OP997609), recA (OP997602 - OP997603), rplB (OP997600 - OP997601), rpoB (OP997598- OP997599), and trpB (OP997594 - OP997595), were extracted from the genome sequences of two strains, ZRIMU1510 and ZRIMU1530, and uploaded to GenBank. Genes for pathogenicity, txtA (OP997593 - OP997594), tomA (OP997596 - OP997597) and Nec1(OP997606 - OP997607), were also identified from the genome sequence and uploaded to GenBank. The housekeeping genes and the pathogenicity genes showed over 98% identity with S. niveiscabiei. Phylogenetic trees were constructed using concatenated housekeeping gene sequences (Kumar et al. 1994) and the cladogram showed that the isolates ZRIMU1510 and ZRIMU1530 grouped with the type strain NRRLB-24457T. Pathogenicity tests were done by drench application of 100 ml spore suspensions (104 CFU/ml) of ZRIMU1530, ZRIMU1510, or phosphate buffer into pots with potato plants (cv. Favorita) grown in potting mix. Five tubers were planted and inoculated with each pathogen or phosphate buffer as the negative control. The plants were then placed in a greenhouse with 12 h of light per day, irrigated regularly, and harvested after 3 months. The newly formed tubers were checked for disease symptoms. Tubers from pots inoculated with ZRIMU1530 and ZRIMU1510 exhibited typical symptoms of common scab with raised corky lesions with deep pits, but the negative controls remained asymptomatic. The pathogens were reisolated from the lesions and confirmed to be identical to the original isolates by 16S rRNA gene sequences, thus completing Koch's postulates. The pot experiment was conducted twice: first in May 2022 and second in February 2023. To our knowledge, this is the first report of S. niveiscabiei causing common scab of potato in Shanxi and Gansu, China. S. niveiscabiei was first reported in Korea (Park et al. 2003) and this report will draw attention to the study and management of scab pathogens in China.

Microencapsulation of Thymus vulgaris and Tagetes minuta essential oils: Volatile release behavior, antibacterial activity and effect on potato yield

Thymus vulgaris and Tagetes minuta essential oils (EOs) are recognized due to their antibacterial activity against Streptomyces scabiei , the main causal agent of potato common scab disease. However, EOs have phytotoxic characteristics and are susceptible to degradation by environmental factors, which make their storage and application difficult. Microencapsulation technology represents an alternative for EOs handle, allowing their protection and gradual spread of their compounds. In the present work, microcapsules of maltodextrin and hydroxypropyl methylcellulose containing T. minuta and T. vulgaris EOs were evaluated, analyzing their features, their stability at storage conditions and the control release of their volatile compounds when they are applied on humid substrate. Additionally, the in vitro antibacterial activity of microencapsulated EOs against S. scabiei, and their effects on potato crop yield were evaluated. The obtained microcapsules presented good yield (48.28–51.01 %), low moisture (3.87–3.98 %), spherical shape, and variable size. The release rate of volatiles was high and constant over the 29 days of storage, for almost every compound detected from microcapsules containing T. vulgaris EO. Additionally, the microcapsules containing T. minuta EO showed a variable but high release rate of its main compound dihydrotagetone. The application of microcapsules on humid substrate resulted in a greater release of volatiles for 14 days. The application of T. vulgaris and T. minuta EOs on potato plants (var. Spunta) showed no effect on plant growth and photosynthetic activity, but reduced tuber yield (9.07 and 9.40 g tubers fresh weight/ plant, respectively). The microencapsulation of these EOs reduced this effect (10.14 and 10.29 g tubers fresh weight/plant, respectively), and maintained the bacteriostatic activity on S. scabiei , making them a promising tool for potato common scab control.

Surfactin secreted by Bacillus amyloliquefaciens Ba01 is required to combat Streptomyces scabies causing potato common scab.

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.

Potato tuber skin proteome is enriched with defensive components to prevent the further infection of common scab into tuber flesh

Potato common scab is a soil-borne disease caused mainly by Streptomyces scabies that seriously affects tuber quality and production. To understand the potential molecular mechanisms of potato tuber responded to common scab, a comparative proteomics approach was applied to analyze the proteome alteration of tuber skin and flesh after infected with common scab by two-dimensional gel electrophoresis (2-DE). Quantitative image analysis showed that the abundance of 36 and 26 protein spots in tuber skin and flesh of scab-infected potato were significantly altered (p < 0.05) more than 1.5-fold, respectively. All these differentially abundant proteins were successfully identified by MALDI-TOF/TOF MS, which were mainly involved in defense, bioenergy and metabolism, storage, chaperones, redox homeostasis, miscellaneous and other unknown functions. Compared with tuber flesh, more defense-related proteins were up-regulated in tuber skin, and several cell wall reorganization and lignification-related enzymes were also up-regulated in tuber skin. It appeared that the tuber skin as a barrier might be enriched with components of defense response to prevent the further infection of pathogen into tuber flesh. Several chaperones were up-regulated in tuber skin and flesh, suggesting a key role in reconstructing normal protein conformation and cell homeostasis in tubers. Conversely, common scab causes the down-regulation of many patatin proteins, which might inhibit tuber swelling. This study would provide some new insight into the potential response mechanisms of tuber infected with common scab, and help in developing strategies to improve resistance to common scab in potato breeding.

The Role of Thaxtomin A and Necrosis Protein in Virulence of Streptomyces scabies that Cause Potato Common Scab Disease

The Role of Thaxtomin A and Necrosis Protein in Virulence of Streptomyces scabies that Cause Potato Common Scab Disease

Transcriptome Analysis of Tryptophan-Induced Resistance against Potato Common Scab.

Potato common scab (CS) is a worldwide soil-borne disease that severely reduces tuber quality and market value. We observed that foliar application of tryptophan (Trp) could induce resistance against CS. However, the mechanism of Trp as an inducer to trigger host immune responses is still unclear. To facilitate dissecting the molecular mechanisms, the transcriptome of foliar application of Trp and water (control, C) was compared under Streptomyces scabies (S) inoculation and uninoculation. Results showed that 4867 differentially expressed genes (DEGs) were identified under S. scabies uninoculation (C-vs-Trp) and 2069 DEGs were identified under S. scabies inoculation (S-vs-S+Trp). Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses indicated that Trp induced resistance related to the metabolic process, response to stimulus, and biological regulation. As phytohormone metabolic pathways related to inducing resistance, the expression patterns of candidate genes involved in salicylic acid (SA) and jasmonic acid/ethylene (JA/ET) pathways were analyzed using qRT-PCR. Their expression patterns showed that the systemic acquired resistance (SAR) and induced systemic resistance (ISR) pathways could be co-induced by Trp under S. scabies uninoculation. However, the SAR pathway was induced by Trp under S. scabies inoculation. This study will provide insights into Trp-induced resistance mechanisms of potato for controlling CS, and extend the application methods of Trp as a plant resistance inducer in a way that is cheap, safe, and environmentally friendly.

A novel of new class II bacteriocin from Bacillus velezensis HN-Q-8 and its antibacterial activity on Streptomyces scabies.

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.

Isolation and identification of an endophytic bacteria Bacillus sp. K-9 exhibiting biocontrol activity against potato common scab.

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 3.82cm. 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.