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Potato common scab (PCS), a significant potato disease, negatively impacts tuber quality. The present study was conducted to isolate and characterize pathogenic Streptomyces species associated with PCS disease in Türkiye based on their morphological, physiological and molecular characteristics. Field‐grown potatoes that exhibited scab lesions were collected from four provinces in 2020–2021, and 200 bacterial isolates were obtained from netted, superficial and deep‐pitted common scab lesions. Pathogenicity assays, including in vitro tuber slice and in planta radish seedling bioassays, identified 150 pathogenic isolates. Morphological and physiological characterization of 92 selected isolates revealed several Streptomyces species that exhibited diverse mycelium colours, sporulation patterns and pigmentation. Molecular analysis using 16S rRNA sequencing, species‐specific primers, PCR‐RFLP of the 16S‐23S (ITS) region with Hpy99I restriction enzyme, and multilocus sequence analysis (MLSA) based on atpD, recA, rpoB and trpB genes revealed that S. scabiei was the dominant species, followed by S. europaeiscabiei, S. caniscabiei, S. bottropensis, S. stelliscabiei and S. turgidiscabies. PCR analysis revealed the presence of the thaxtomin synthetase genes (txtAB) in all tested samples, while the necrogenic protein (nec1) and tomatinase (tomA)‐encoding genes were absent from three and two isolates, respectively. Phylogenetic analysis of 32 representative isolates conducted with sequences from 16S rRNA, species‐specific PCR and MLSA confirmed their morphological identification and clustered them with reference strains. This study contributes to the understanding of distribution of Streptomyces species associated with PCS, and to our knowledge, is the first molecular confirmation of S. caniscabiei and S. turgidiscabies causing potato scab in Türkiye. [ABSTRACT FROM AUTHOR]

This study was aimed to identify major species of Streptomyces that are able to cause potato common scab in Egypt. Potato tubers showing typical symptoms of common scab disease were collected from three different regions of Upper Egypt. The causal pathogens were isolated, and morphological, biochemical and pathogenicity tests were conducted in vitro to preliminary identify the isolated Streptomyces isolates. Moreover, the partial 16S rDNA gene sequencing was used to genetically identification of the isolates. Four new pathogenic species that have not previously been reported in Egypt were identified. Four species of Streptomyces rochei, S. rutgersensis, S. lateritius, and S. bottropensis were identified. Isolates S1, S10, S14, S17, S18, S20, and S21 were identified as Streptomyces rochei, isolates S11 was identified as S. rutgersensis, isolates S13 identified as S. lateritius and isolates S15 was identified as S. bottropensis. To the obtained data, this is the first report that S. rochei, S. rutgersensis, S. lateritius, and S. bottropensis cause of potato common scab disease in Egypt. The different of obtained 16S rDNA sequences were deposited at NCBI GenBank with the following accession numbers: (S1) MZ267260, (S10) MZ267264, (S14) MZ267268, (S17) MZ267271, (S18) MZ267272, (S20) MZ267274, (S21) MZ267275, (S11) MZ267265, (S13) MZ267267, and (S15) MZ267269. The four newly identified isolates showed different pathogenicity, morphological and biochemical characteristics. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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

Potato common scab (Streptomyces scabies) is a widespread disease and highly prevalent in recent years in the one cropping zone of northern China, the mixed cropping zone of southwestern China, and the two cropping zone of the Central Plains. The selection and breeding of potato common scab- resistant varieties is the most effective and economical method. The common scab resistance and the yield were evaluated for 31 potato varieties (lines) in 2022 by natural disease nursery method. In 2023, the 12 potato varieties (lines) identified in previous year were repeatedly evaluated. Among the 31 varieties (lines) tested in 2022, 11 potato varieties (lines), including 'Xisen 5', 'Z496', 'Z740', 'Z759', 'Z760', 'Z812', 'Z917', 'Z962', 'Z1148', 'Z1152' and 'Z1356', were resistant and their yields performed well. The repeated test results in 2023 showed that the 'Z962' was resistant to common scab (R) for two years, and there was no significant difference in yield compared with the local main variety 'Youjin'. The yields of 'Z1148', 'Z1152', 'Z1356', 'Z740', 'Z760' and 'Z917' were higher than those of the local main variety, but only the yield of 'Z740' was significantly different from the control, and was moderately resistant (MR) to common scab. 'Xisen 5' and 'Z496' were highly resistant to common scab and could be used as parent materials to create hybrid combinations for common scab resistance breeding. In this study, 31 potato materials were evaluated and screened for common scab resistance, which would provide basic materials for common scab resistance breeding, disease prevention and control. [ABSTRACT FROM AUTHOR]

Every land plant exists in a close relationship with microbial communities of several niches: rhizosphere, endosphere, phyllosphere, etc. The growth and yield of potato—a critical food crop worldwide—highly depend on the diversity and structure of the bacterial and fungal communities with which the potato plant coexists. The potato plant has a specific part, tubers, and the soil near the tubers as a sub-compartment is usually called the "geocaulosphere", which is associated with the storage process and tare soil microbiome. Specific microbes can help the plant to adapt to particular environmental conditions and resist pathogens. There are a number of approaches to modulate the microbiome that provide organisms with desired features during inoculation. The mechanisms of plant–bacterial communication remain understudied, and for further engineering of microbiomes with particular features, the knowledge on the potato microbiome should be summarized. The most recent approaches to microbiome engineering include the construction of a synthetic microbial community or management of the plant microbiome using genome engineering. In this review, the various factors that determine the microbiome of potato and approaches that allow us to mitigate the negative impact of drought and pathogens are surveyed. [ABSTRACT FROM AUTHOR]

Potato common scab is a common soil-borne disease worldwide, which is caused by Streptomyces spp. In order to screen Bacillus ssp. that may have a good inhibitory effect on scab pathogen, plate antibacterial tests in laboratory were conducted for determination of antibacterial activity, and the phylogenetic tree was constructed for molecular identification of Bacillus species based on gyrB sequence by neighbor joining (NJ) method. The inhibition effect of 13 strains of Bacillus on S. scabies HP4 was detected, and it was found that the inhibition zone diameter of the five strains of BEV2, BAM7, GF3, BPU6 and BMO8 on S. scabies HP4 was greater than 9.0 mm. BEV2 and GF3 were identified as B. velezensis, BAM7 as B. amyloliquefaciens, BPU6 as B. pumilus, and BMO8 as B. mojavensis based on the phylogenetic tree. The antibacterial activity of four strains of Bacillus and their combinations against three pathogenic bacteria were determined. Among them, BEV2+BAM7 had an inhibitory circle diameter of at least (29.5 ± 2.7) mm against pathogenic Streptomyces. When multiple pathogenic Streptomyces appeared simultaneously, it still showed good inhibitory effect, indicating that BEV2+BAM7 have a stable control effect on various potato common scab pathogens. In this experiment, various strains of Bacillus that antagonize different pathogenic Streptomyces are screened, which could expand the antibacterial spectrum against potato common scab and improve the stability of disease prevention and control effects. This may lays the foundation for the biological control of potato common scab and the development of biological agents. [ABSTRACT FROM AUTHOR]

Common scab (CS) caused by pathogenic Streptomyces spp. plays a decisive role in the qualitative and quantitative production of potatoes worldwide. Although the CS pathogen is present in Assam’s soil, disease signs and symptoms are less obvious in the landrace Rongpuria potatoes that indicate an interesting interaction between the plant and the geocaulosphere microbial population. Toward this, a comparative metagenomics study was performed to elucidate the geocaulosphere microbiome assemblages and functions of low CS-severe (LSG) and moderately severe (MSG) potato plants. Alpha diversity indices showed that CS occurrence modulated microbiome composition and decreased overall microbial abundances. Functional analysis involving cluster of orthologous groups (COG) too confirmed reduced microbial metabolism under disease incidence. The top-three most dominant genera were Pseudomonas (relative abundance: 2.79% in LSG; 12.31% in MSG), Streptomyces (2.55% in LSG; 5.28% in MSG), and Pantoea (2.30% in LSG; 3.51% in MSG). As shown by the high Pielou’s J evenness index, the potato geocaulosphere core microbiome was adaptive and resilient to CS infection. The plant growth-promoting traits and potential antagonistic activity of major taxa (Pseudomonads, non-pathogenic Streptomyces spp., and others) against the CS pathogen, i.e., Streptomyces scabiei, point toward selective microbial recruitment and colonization strategy by the plants to its own advantage. KEGG Orthology analysis showed that the CS infection resulted in high abundances of ATP-binding cassette transporters and a two-component system, ubiquitous to the transportation and regulation of metabolites. As compared to the LSG metagenome, the MSG counterpart had a higher representation of important PGPTs related to 1-aminocyclopropane-1-carboxylate deaminase, IAA production, betaine utilization, and siderophore production. [ABSTRACT FROM AUTHOR]

Potato common scab caused by the actinobacterium Streptomyces scabiei is characterized by the formation of corky lesions on tubers that reduce their marketability. Management of common scab is very complex and often ineffective under various environmental conditions. Using potato varieties that are more resistant to common scab remains one of the most efficient strategies to control this disease. However, very little is known about the factors associated with resistance to common scab. Somaclone RB9 regenerated from thaxtomin A‐habituated potato Russet Burbank calli produced tubers more resistant to common scab than the original variety. Comparison of the RB9 tuber proteome with that of Russet Burbank using label‐free quantitative proteomic analysis revealed changes in the accumulation of defence‐related proteins from the patatin and lipoxygenase (LOX) families, which are involved in the metabolism of lipids, and of two miraculins of the Kunitz‐type protease inhibitors family. The implication of LOX during common scab infection was studied using synchronized minitubers developed from leaf‐bud cuttings. S. scabiei infection stimulated the accumulation of LOX in both Russet Burbank and RB9 minitubers, but this accumulation was intensified in RB9 minitubers. Infection also increased LOX activity in Russet Burbank and RB9 minitubers. However, LOX activity measured in noninfected RB9 minitubers was similar to that of infected Russet Burbank minitubers, indicating endogenous activation of LOX activity in RB9 minitubers. We discuss how increased LOX abundance and activity in the somaclone RB9 may contribute to improving tuber defence against common scab. [ABSTRACT FROM AUTHOR]

Beneficial soil and crop management practices, such as longer rotations, cover crops and green manures, organic amendments, and reduced tillage, may improve soil and crop health and productivity when incorporated into cropping systems. Long-term trials are needed to assess the full impacts and effects of these systems. In field trials originally established in 2004, three different 3-yr potato cropping systems focused on management goals of soil conservation (SC), soil improvement (SI), and disease suppression (DS) were evaluated and compared to a standard 2-yr rotation (SQ) and a nonrotation control (PP). After 12–15 years and results compiled over a four-year period (2015–2018), the SI system (with history of compost amendments) increased total and marketable tuber yields relative to all other systems, with yields averaging 26 to 36% higher than the standard SQ system and 36 to 59% greater than PP. SI also improved soil properties such as organic matter and soil water content, nutritional characteristics, and microbial activity compared to the other systems. The SI system continued to provide these improvements several years after compost amendments ended, indicating the long-term benefits. The DS system, which included a disease-suppressive green manure rotation crop and fall cover crops, also improved yield (by 16–20%), had higher organic matter content (by 12%), and increased microbial activity (by 22%) relative to SQ, as well as reducing the soilborne tuber diseases black scurf and common scab by 10–30%. The nonrotation PP system resulted in the notable degradation of soil properties and yield over time. These results demonstrate that soil health management practices can be effectively incorporated into viable potato cropping systems to improve soil properties and crop health, and may enhance long-term sustainability. [ABSTRACT FROM AUTHOR]

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. [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]

Adequate integrated management of potato leaf diseases can have an influence on pathogens which are challenging to control and cause main potato tuber diseases. Deriving from this hypothesis, an experiment was designed to evaluate the efficacy of foliar application of twelve fungicides on late blight in tubers, common scab, black scurf and silver scurf. In the period of 2013 to 2017, the fungicides were equally applied six times in registered doses during the growing seasons. Eight tuber disease indicators and eight yield characteristics were then evaluated in harvested tuber samples. Significant differences were found among the fungicides used. In comparison to the negative control (n. c.), the application of Infinito, Ranman Top and Revus Top reduced the quantity of tubers infected by late blight by 72% on average. The incidence of common scab increased by 65% of n. c. under the effect of copper oxychloride, while an average reduction by 19% of n. c. was observed with the use of Acrobat MZ WG, Curzate Gold and Consento. The occurrence of silver scurf was significantly enhanced by Curzate Gold and Consento (105% of n. c.), while it was suppressed by Revus Top and Revus (85% of n. c.). All fungicides were ineffective on black scurf yet had a positive influence on the potato yield and quality, with the choice of fungicide having a great impact on the quality of tubers. The application of any safe fungicide is important, especially in years similar to 2015, which was the most devastating recent year for potato production in terms of structural changes in yield of tubers. [ABSTRACT FROM AUTHOR]

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]

In North America, potato early dying is often controlled using soil fumigants. Fumigants confer benefits on plant health but also impact soil microbial activity, including nitrogen (N) cycling. The purpose of this study was to evaluate the effects of two soil fumigants, chloropicrin and metam sodium, on potato crop yield, N uptake, and N use efficiency (NUE), as well as soilborne pathogens, soil microbial respiration rates and soil concentrations of NH4+-N and NO3−-N. We established a field study with a split-plot randomized complete block design in 2016 and 2017, with whole plots divided among three fumigation treatments (no fumigant, chloropicrin, or metam sodium) and split into five subplots, each receiving a different total application rate of N (45, 135, 202, 269, or 336 kg·ha−1 N). Both fumigants suppressed Verticillium dahliae propagule concentrations and foliar symptoms of potato early dying while increasing yield, final tuber set, N uptake, and NUE. Fumigation did not affect the agronomic optimum N rate, nor the response of marketable yield to N rate, but it did increase yield per unit N applied (partial factor productivity) by 16% and 35% over the non-fumigated controls in 2016 and 2017, respectively. Chloropicrin, but not metam sodium, reduced the prevalence of common scab symptoms in tubers. Both fumigants decreased microbial respiration rates before planting and at midseason. Fumigants reduced nitrification rates before planting and at midseason, with chloropicrin having a particularly strong effect before planting. While fumigation conferred benefits to yield and NUE, its effects on microbial community structure and function merit further study. [ABSTRACT FROM AUTHOR]

Common scab is a soilborne disease that occurs in potato worldwide. Scab is usually present superficially on potato tubers but nonetheless reduces marketability. A genome-wide association study for common scab resistance was performed using 13,002 genome-wide SNPs, with 165 genotypes mostly for chip-processing. We identified a novel QTL for common scab resistance that explained at most 14.7% of the total variance; this QTL was within the 640 kb interval between 0.43 Mb and 1.07 Mb on potato chromosome 1. Recessive homozygosity at this QTL increased levels of resistance. There is no agreement in terms of the locations of QTLs and their genetic modes between the results of previous studies and the present study or among any study. As such, common scab resistance is a highly complex trait, as the QTLs discovered to date are all minor-effect QTLs. [ABSTRACT FROM AUTHOR]

Common scab (CS) is a potato disease that significantly decreases the market value of potato tubers after the development of necrotic lesions on their surface. Streptomyces scabiei is the main causal agent of CS; however, other closely related species, including S. acidiscabies and S. turgidiscabies, have also been shown to cause the disease. In this study, we characterized the genetic and phenotypic diversity of Streptomyces spp. causing CS in Prince Edward Island, the main potato-producing province in Canada. Two hundred and ninety-six pathogenic Streptomyces spp. isolates were retrieved from diseased tubers harvested from six fields located across a longitudinal geographical gradient. Genome fingerprinting analyses using repetitive elements PCR (ERIC- and BOX-PCR) revealed 14 distinct genetic groups. Thirteen groups were taxonomically affiliated with S. scabiei, whereas the fourteenth group was affiliated with S. acidiscabies. Their geographical distribution was characterized and revealed that on average between six and eight different genetic groups were detected per field, with variable abundance. Virulence assays showed strong differences in virulence between the genetic groups, ranging from low to highly virulent. Interestingly, pathogenic Streptomyces spp. populations in each field seem to be dominated by the most virulent genetic groups. The results obtained will contribute to better understanding of the population dynamic of pathogenic Streptomyces spp. causing CS of potato and promoting the development of more efficient detection and intervention tools to manage this important potato disease. [ABSTRACT FROM AUTHOR]

Common scab of potato caused by pathogenic Streptomyces species poses an economic burden to commercial potato cultivation. Despite decades of research, no molecular markers linked to this trait are currently available, making the development of scab resistant potato varieties inefficient. We evaluated common scab lesion type and tuber coverage in 198 individuals segregating for common scab resistance in replicated field trials with high natural disease pressure over two growing seasons. To identify genetic features associated with resistance, we genotyped the tetraploid (4x) population and parental lines (Kalkaska and Tundra) using the Illumina Infinium 8303 Potato Array and conducted genome-wide association analysis. Here, we report two significant single nucleotide polymorphism (SNP) markers on chromosome 1 associated with both scab traits in both years as well as a SNP marker on chromosome 2 associated with scab tuber coverage. Gene expression profiling of the parents of this population in response to Thaxtomin A treatment revealed differential expression of genes in tubers putatively involved in cell wall biosynthesis and hormone signaling. [ABSTRACT FROM AUTHOR]

In this paper, we aimed at assessing the best conditions for the isolation of actinobacteria from old potato samples. A set of media and pretreatments were tested. The optimal were chosen for the isolation of actinobacteria from potatoes from Peru, Chile and Argentina. Isolates were tested on the presence of thaxtomin phytotoxin by amplification of the respective gene. Phylogenetic position of strains was compared with their geographical origin, pathogenic potential and existence of common scab (CS) symptoms on potato sample. We demonstrated that RNAlater can be successfully used for the long-term preservation of potato peel for subsequent isolation of actinobacteria on R2A medium. Many streptomycetes were thaxtomin-positive, though they are distantly-related to described pathogens causing CS. Genus Nocardia was first reported to be thaxtomin-positive. Potentially pathogenic strains were isolated not only from infected potato but also from those lacking CS symptoms. Some strains from scabby potatoes were thaxtomin-negative. [ABSTRACT FROM AUTHOR]

[ Objective]The changes of physiological characteristics of different resistant potato varieties inoculated with potato common seal) bacteria were studied to provide theoretical basis for rapid screening and cultivation of resistant potato varieties. [ Method]The physiological and biochemical indexes of potato common seal) resistance were determined, and the activities of peroxidase (POD) , superoxide dismutase (SOD) , polyphenol oxidase ( PPO) ,malondialdehyde in resistant and susceptible potato treated with potato common scab were analyzed. [ Result]The results showed that the contents of POD, SOD and PPO were increased after potato tubers were inoculated with potato common scab. Among them, the activity of disease-resistant varieties POD PPO after inoculation was significantly higher than that of susceptible varieties. SOD activity of potato tubers was decreased, increased and then decreased after potato common scab infection, and the enzyme content of susceptible cultivars was higher than that of resistant eultivars. Inoculation of scab promoted the increase of MDA content in susceptible eultivars, and MDA content in susceptible cultivars was always higher than that in resistant cultivars. [ Conclusion] POD, SOD, PPO increased in different degree in tubers inoculated with common scab, but the activity of PAL did not change after inoculation. POD activity and PPO activity in tuber of resistant cultivars remained at a high level before and after inoculation, while the activity of POD activity PPO in tuber of susceptible cultivars was relatively low, indicating that POD activity and PPO activity in tuber played an active role in resisting scab infection of potato varieties. SOD activity of susceptible cultivars was significantly higher than that of resistant cultivars before and after inoculation. Resistant cultivars showed a trend of decreasing first and then increasing after inoculation. After inoculated with different resistant potato tubers, MDA content in susceptible varieties increased, and that of susceptible varieties was higher than that of resistant varieties, indicating that cells and biofilm of susceptible varieties were destroyed more seriously. In con elusion, POD activity, PPO activity, SOD activity, soluble sugar content, MDA content may be used as auxiliary means of the resistance i dentification for potato to common seal). [ABSTRACT FROM AUTHOR]

Antimicrobial potential of Controller, Impose, Phostrol, Ridomil Gold plus and Roxyl Plus was determined for Pectobacterium atrosepticum and Streptomyces scabies. The cidal effect against P. atrosepticum was only shown by the fungicide Controller. S. scabies was highly affected by Controller, Impose and Roxyl plus compared to RidomilGold plus and Phostrol that did not inhibit the growth. The MIC of Controller was found to be 4000 ppm for P. atrosepticum and S. scabies. On the other hand, the MICs of Impose and Roxyl Plus were found to be 4000 ppm and 3000 ppm respectively for S. scabies. Application of Controller against blackleg significantly decreased the incidence of the disease in potted potato plants. Application of Controller, Impose and Roxyl Plus at 3.0g/I to control common scab significantly decreased the disease. Conclusive results were obtained by the 4.0 g/I application. Residues of ingredients of these fungicides in potato tuber 60 day after application were below the approved maximum residue level (MRL). [ABSTRACT FROM AUTHOR]

Common scab caused by Streptomyces species is an important disease worldwide. Huge economic losses are faced because of the disease every year and control options are scant. This study was conducted to develop effective biocontrol agents, which have capability of enhancing potato yield. A total of 1048 bacterial isolates from former studies were tested against S. scabiei in-vitro and 22 out of these strains were found to be effective. Most effective four strains (KBA- 10, K-19B, TV-91C and RK-92) were chosen for field trials. All four strains can fix nitrogen and dissolve phosphate. According to the result, KBA-10, TV-91C, RK-92 and K-19B have biocontrol efficacy of 60.35%, 37.2%, 33.5% and 18.7%, respectively. They increased potato yield 40.0%, 41.1%, 25.52% and 20.42 %, respectively, compared to control. Increases provided by KBA-10, K-19B and TV-91C were found to be statistically significant. Biocontrol efficacies of K- 19B, TV-91C and RK-92 were of lesser degree, compared to KBA-10. Additionally, KBA-10 generated an extensive rise (71.7%) in tuber number. KBA-10 can be a good biocontrol agent for reducing potato scab disease and enhancing crop yield. Moreover, KBA-10 can be used in tuber seed production. [ABSTRACT FROM AUTHOR]

Potato (Solanum tuberosum) is a staple food crop and is considered one of the main sources of carbohydrates worldwide. Late blight (Phytophthora infestans) and common scab (Streptomyces scabies) are two of the primary production constraints faced by potato farming. Previous studies have identified a few resistance genes for both late blight and common scab; however, these genes explain only a limited fraction of the heritability of these diseases. Genomic selection has been demonstrated to be an effective methodology for breeding value prediction in many major crops (e.g., maize and wheat). However, the technology has received little attention in potato breeding. We present the first genomic selection study involving late blight and common scab in tetraploid potato. Our data involves 4,110 (Single Nucleotide Polymorphisms, SNPs) and phenotypic field evaluations for late blight (n=1,763) and common scab (n=3,885) collected in seven and nine years, respectively. We report moderately high genomic heritability estimates (0.46 ± 0.04 and 0.45 ± 0.017, for late blight and common scab, respectively). The extent of genotype-by-year interaction was high for late blight and low for common scab. Our assessment of prediction accuracy demonstrates the applicability of genomic prediction for tetraploid potato breeding. For both traits, we found that more than 90% of the genetic variance could be captured with an additive model. For common scab, the highest prediction accuracy was achieved using an additive model. For late blight, small but statistically significant gains in prediction accuracy were achieved using a model that accounted for both additive and dominance effects. Using whole-genome regression models we identified SNPs located in previously reported hotspots regions for late blight, on genes associated with systemic disease resistance responses, and a new locus located in a WRKY transcription factor for common scab. [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 is one of the most important diseases affecting potato crops worldwide. Using fresh residues and/or bio-products of Canadian goldenrod (Solidago canadensis) may offer an alternative to harmful conventional fumigants. In this study, we aimed to: (i) conduct a preliminary investigation of the utilization ofS. canadensisto reduce common scab severity (Experiment 1), and (ii) determine the allopathic potentials ofS. canadensisextracts onStreptomyces scabiei(also known asS. scabies), the most important soil pathogen responsible for causing common scab in North America (Experiment 2). Compared with control plants, preliminary results showed that adding 1.2 kg of freshS. canadensisresidue per m2reduced scab severity by about 45% (Experiment 1). Furthermore, hexane and dichloromethane extracts ofS. canadensis, at a concentration of 200 µg·mL−1, inhibited the growth ofS. scabieiby about 97% (Experiment 2). These results were comparable with those using tetracycline (2.5 µg·mL−1), a known inhibitor ofS. scabiei. Both experiments suggested thatS. canadensismay represent a new approach for controlling potato common scab. More studies are required to better understand the mechanisms involved inS. canadensisinduced reduction of common scab in order to standardize the approaches. La gale commune est une maladie tellurique importante chez la pomme de terre et l’utilisation de résidus et/ou extraits de verge d’or du Canada (Solidago canadensis) pourrait représenter une alternative prometteuse aux pesticides (fumigants) utilisés pour combattre la maladie. Les objectifs de cette recherche étaient i) effectuer une expérience préliminaire afin de mesurer les effets de l’incorporation de résidus frais deS. canadensissur la sévérité de la gale commune (expérience 1) et ii) déterminer les potentiels allélopathiques des extraits de S.canadensissurStreptomyces scabiei, un important agent pathogène causant la maladie de la gale commune (expérience 2). Nos résultats préliminaires issus de l’expérience 1 montrent qu’ajouter 1.2 kg m−2deS. canadensis(résidus frais) permet de réduire significativement de 45% la sévérité de la gale commune. Les extraits deS. canadensiseffectués avec l’hexane et le dichlorométhane et à des concentrations de 200 µg mL−1permettent d’inhiber à 97% la croissance deS. scabiei, résultats comparables à la tétracycline (2.5 µg mL−1), un antibiotique connu pour inhiber la croissance deS. scabiei. Les résultats de cette étude montrent clairement et pour une première fois le potentiel d’utilisation deS. canadensiscomme moyen de lutte contre la maladie de la gale commune chez la pomme de terre. D’autres recherche seront toutefois nécessaires pour bien comprendre et cibler les mécanismes impliqués afin de standardiser et d’optimiser cette nouvelle et prometteuse approche. [ABSTRACT FROM AUTHOR]

Streptomyces scabies, causative agent of common scab of potato, produces the phytotoxins concanamycin and thaxtomin. In a potato tuber slice assay to study the contribution of concanamycins to lesion development, concanamycin A had weak necrosis-inducing activities; >10× the amount of thaxtomin A was needed to produce equivalent lesion severity. Concanamycins were detected in tubers inoculated with S. scabies, which caused deep-pitted lesions but not in those inoculated with Streptomyces acidiscabies, which caused corky, raised lesions. In field-grown, diseased potatoes, concanamycin content tended to be higher in tubers with deep-pitted lesions than in those with corky, raised lesions. [ABSTRACT FROM AUTHOR]

Common scab, caused by species from the bacterial genus S treptomyces, is an important disease of potato ( S olanum tuberosum) crops worldwide. Early tuberization is a critical period for pathogen infection; hence, studies of host gene expression responses during this developmental stage can be important to expand our understanding of the infection process and to identify putative resistance genes. In an infection experiment with the highly susceptible potato cultivar Saturna and the relatively resistant cultivar Beate, transcription profiles were obtained by RNA sequencing at two developmental stages: the early hook stage and the early tuber formation stage. Our results indicate that 'Beate' mounts an early and sustained response to infection by S . turgidiscabies, whereas the defence response by 'Saturna' ceases before the early tuber formation stage. Most pronounced were the putative candidate defence-associated genes uniquely expressed in 'Beate'. We observed an increase in alternative splicing on pathogen infection at the early hook stage for both cultivars. A significant down-regulation of genes involved in the highly energy-demanding process of ribosome biogenesis was observed for the infected 'Beate' plants at the early hook stage, which may indicate an allocation of resources that favours the expression of defence-related genes. [ABSTRACT FROM AUTHOR]

The genes conferring pathogenicity in S treptomyces turgidiscabies, a pathogen causing common scab of potato, are grouped together on a pathogenicity island ( PAI), which has been found to be mobile and appears to transfer and disseminate like an integrative and conjugative element ( ICE). However, in S treptomyces scabiei, another common scab-inducing species, the pathogenicity genes are clustered in two regions: the toxicogenic region ( TR) and the colonization region. The S . scabiei 87.22 genome was analysed to investigate the potential mobility of the TR. Attachment sites ( att), short homologous sequences that delineate ICEs, were identified at both extremities of the TR. An internal att site was also found, suggesting that the TR has a composite structure ( TR1 and TR2). Thaxtomin biosynthetic genes, essential for pathogenicity, were found in TR1, whereas candidate genes with known functions in recombination, replication and conjugal transfer were found in TR2. Excision of the TR1 or TR2 subregions alone, or of the entire TR region, was observed, although the excision frequency of TR was low. However, the excision frequency was considerably increased in the presence of either mitomycin C or S treptomyces coelicolor cells. A composite TR structure was not observed in all S . scabiei and S treptomyces acidiscabies strains tested. Of the ten strains analysed, seven lacked TR2 and no TR excision event could be detected in these strains, thus suggesting the implication of TR2 in the mobilization of S . scabiei TR. [ABSTRACT FROM AUTHOR]

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. • This study first investigated the potential proteomic dynamics in common scab-infected potato tuber skin and flesh. • The tuber skin as a barrier might be enriched with defensive components to prevent the further infection of pathogen into tuber flesh. • The storage protein accumulation of common scab-infected tuber was inhibited, which might further inhibit tuber swelling. • It will provide some references for the explanation of S. scabies infection process, and further develop strategies to improve common scab resistance in potato breeding. [ABSTRACT FROM AUTHOR]

Common scab (CS) of potato, caused by Streptomyces scabies, is an important disease in the US. CS problems can be avoided using resistant varieties. However, evaluating breeding clones can be complicated by high location and season-based soil and environmental variation. In this study we evaluated the efficacy of screening for CS resistance within the Wisconsin breeding program across multiple environments from 2006 to 2013. In each trial, 60-160 clones were evaluated. We compared the ability to select for CS resistance in a set of 18 dedicated CS screening trials (DST) versus 18 similar parallel standard breeding trials (SBT). Heritability for CS rating across DST was 0.83 vs. 0.53 in SBT. Data analysis from DST was able to separate CS susceptible cultivars (Atlantic, Snowden) from resistant cultivars (Pike, Snowden). However, same data analysis from SBT was not able to separate susceptible from resistant cultivars. Using DST datasets, we estimated the genotypic stability of scab performance across years and locations. We also calculated the probability distributions for the better or worse performance of a given clone vs. a standard variety. Using results from six or more DST we identified five round white clones that outperformed or matched CS tolerant Pike, eleven russet clones that outperformed or matched CS tolerant Russet Burbank and five red or yellow skin clones that outperformed or matched CS resistance level of Dark Red Norland. The approaches utilized here offer useful additional information for breeding programs which aim to improve selection efficiency for scab resistance. [ABSTRACT FROM AUTHOR]

Developing chipping cultivars with improved tuber quality and disease resistance is a major interest for breeders and the potato industry. A popular chipping cultivar 'Atlantic', is desired for its high yield and gravity. However, this cultivar suffers from poor internal tuber quality and high scab susceptibility. On the contrary, cultivar 'Superior' is known to have excellent tuber internal quality and moderately scab resistance. In addition, this cultivar is known to have high tuber calcium as compared to 'Atlantic'. The present study intended to generate populations that can be suitable for the genetic study of tuber calcium, internal quality, common scab, and other commercially important traits such as yield, specific gravity and chip quality at the tetraploid level. Two populations obtained by reciprocally crossing the cultivars 'Atlantic' and 'Superior' were evaluated during 2009 to 2012 at Hancock, Wisconsin. Significant genotype effects and moderately low to high broad-sense heritabilities were identified for all traits evaluated indicating that the observed phenotypic variation has an important genetic component. In addition, the parents differed significantly for all traits across trials, and most genotypes performed in between the two parents but some genotypes were more extreme than the parents. Furthermore, evidence of reciprocal effects was found for some traits. In addition to learning about the genetics of these important traits we were able to identify some genotypes that combined the commercially desired traits of the two cultivars. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate certain fungicides againstStreptomyces scabies(Thaxter), the main causal agent of common scab disease in potato and other crops,in vitroandin vivo. Fourteen isolates ofS. scabieswere isolated from naturally infected potato tubers showing common scab symptoms. All isolates were pathogenic to potato tubers and produced typical symptoms of common scab. Isolate (No. 11) caused highest disease index (DSI) followed by isolates 10, 8 and 5 (61.13%). Seven fungicides (Rizolex, Capitan, Moncut, Ridomil, Maxim, Topsin, and Oxyplus) were screenedin vitrofor their toxicity against the pathogen isolate (No. 11). Results showed that four of them (Rizolex, Capitan, Moncut, and Ridomil) exhibited inhibition zone ranging from 5.33 to 26.33?mm. Capitan, Ridomil, and Rizolex were able to reduce DSI under field condition but they varied in their effects. Capitan was the best fungicide which aids in the reduction of disease (33.8%) followed by Ridomil (31.5%) while Rizolex (21.2%) was the lowest one. [ABSTRACT FROM AUTHOR]

Streptomyces scabies causes yield losses in potato by inducing common scab ( CS) symptoms on tubers. Little information is available on global gene expression responses in CS-causing streptomycetes upon interaction with host plants. In this study, expression of 8746 genes was analysed in the type strain of S. scabies ( ATCC49173) using a custom-designed, gene-specific oligonucleotide microarray. Bacteria were grown in liquid yeast malt extract ( YME) medium and 480 genes were found to be up-regulated 24 h after supplementing the cultures with potato microtubers. Quantitative PCR analysis of eight putative or known virulence genes was consistent with the microarray data. Elevated expression of the thaxtomin synthesis gene txtA and txtR genes regulating synthesis of thaxomin A, the main pathogenicity factor of S. scabies, and production of thaxtomin A were detected in cultures containing microtubers. Unexpectedly, thaxtomin was also detected in cultures lacking microtubers, which indicated that growth in YME induces thaxtomin production in S. scabies. Many but not all microtubers incubated in the cultures of S. scabies for 48 h displayed symptoms, indicating that the microtubers were not equally susceptible even though they were produced under uniform in vitro growth conditions. These factors may have limited the differences in gene expression observed between S. scabies exposed to microtubers compared to controls. This study provides some of the first results on the transcriptome of S. scabies, a widely distributed and important potato pathogen, upon exposure to young developing potato tubers. The findings will inform future studies on interactions of CS-inducing streptomycetes with potato and means to control the disease. [ABSTRACT FROM AUTHOR]

Background: Suberin is a recalcitrant plant biopolymer composed of a polyphenolic and a polyaliphatic domain. Although suberin contributes to a significant portion of soil organic matter, the biological process of suberin degradation is poorly characterized. It has been suggested that Streptomyces scabiei, a plant pathogenic bacterium, can produce suberin-degrading enzymes. In this study, a comparative analysis of the S. scabiei secretome from culture media supplemented or not with potato suberin was carried out to identify enzymes that could be involved in suberin degradation. Methods: S. scabiei was grown in the presence of casein only or in the presence of both casein and suberin. Extracellular proteins from 1-, 3- and 5-day-old supernatants were analyzed by LCMS/MS to determine their putative functions. Real-time RT-PCR was performed to monitor the expression level of genes encoding several proteins potentially involved in suberin degradation. Results: The effect of suberin on the extracellular protein profile of S. scabiei strain has been analyzed. A total of 246 proteins were found to be common in the data sets from both casein medium (CM) and casein-suberin medium (CSM), whereas 124 and 139 proteins were detected only in CM or CSM, respectively. The identified proteins could be divided into 19 functional groups. Two functional groups of proteins (degradation of aromatic compounds and secondary metabolism) were only associated with the CSM. A high proportion of the proteins found to be either exclusively produced, or overproduced, in presence of suberin were involved in carbohydrate metabolism. Most of the proteins included in the lipid metabolism class have been detected in CSM. Apart from lipid metabolism proteins, other identified proteins, particularly two feruloyl esterases, may also actively participate in the breakdown of suberin architecture. Both feruloyl esterase genes were overexpressed between 30 to 340 times in the presence of suberin. Conclusion: This study demonstrated that the presence of suberin in S. scabiei growth medium induced the production of a wide variety of glycosyl hydrolases. Furthermore, this study has allowed the identification of extracellular enzymes that could be involved in the degradation of suberin, including enzymes of the lipid metabolism and feruloyl esterases. [ABSTRACT FROM AUTHOR]

Aims The primary objective of these experiments was to reduce pathogenicity and virulence of endemic soil pathogenic Streptomyces strains that cause potato common scab ( CS) using nonpathogenic Streptomyces strains to suppress CS in a field situation. Methods and Results Nonpathogenic Streptomyces strains that had shown potential for mitigating CS in greenhouse assays were used in Michigan and Pennsylvania fields known to have high CS disease pressure. Five biocontrol ( BC) strains and three potato cultivars were used in 2009, and three BC strains and three cultivars were used in 2010 in each location. The effects of BC strains on CS disease incidence and severity differed between locations, years and potato cultivars. When overall means of individual BC treatments were compared with nontreated controls, CS incidence and severity were decreased by all BC strains in PA2009, PA2010 and MI2010, particularly in cultivar ' Yukon Gold' in MI. Biocontrol treatments also significantly shifted the proportions of superficial, raised and pitted lesion types in some cultivar/biocontrol treatment combinations. Conclusions All BC strains significantly reduced CS incidence and severity on ' Yukon Gold' in three of four trials, and one BC strain significantly improved the lesion severity profile in cultivar ' Atlantic'. No BC strain significantly reduced CS incidence and severity on all potato cultivars in the different years and locations. Significance and Impact of the Study Several nonpathogenic Streptomyces strains showed potential to reduce CS incidence and severity on two important potato-chipping cultivars in the field. These results can be further applied to reduce CS disease severity in potatoes. [ABSTRACT FROM AUTHOR]

Highlights: [•] Chestnut tissues, essential oils, horseradish, and Bacillus strain BAC03 reduced scab in condition-controlled trials. [•] The efficacy by chestnut tissues, oregano essential oils, and horseradish varied depending on locations and seasons. [•] BAC03 significantly reduced the scab diseases and may increase the plant growth confirmed by field trials. [Copyright &y& Elsevier]

Potato is one of the most important crops in the world and the common scab caused byStreptomycesspecies is a serious disease. To control the disease, agronomical, chemical and biological methods are commonly applied; however, the introduction of resistance into cultivated potatoes has been considered to be the most promising approach. Therefore, in this study, the authors identified resistant breeding lines derived from somatic hybrids that were produced by protoplast fusions betweenSolanum brevidensandSolanum tuberosum. Initially,in vitroassay was applied to select resistant interspecific hybrids, but field assays were also performed to develop resistant breeding lines and populations. Although chromosome number and crossability were not completely recovered back to the cultivated potatoes on somatic hybrids and backcross populations, breeding lines and populations with resistance to common scab that could be used for further breeding were developed. Finally, four BC2populations were selected and tested for resistance to the common scab and for productivity. There were variations in resistance to the common scab within each line and in productivity between lines, but the average percentages of tuber surface area with disease symptom in BC2lines were approximately 85% and 46% less than the commercial parent controls, ‘Dejiam’ and ‘Superior’, respectively and the productivities of two populations recovered by 80–103% and 90–115% relative to ‘Dejiam’ and ‘Superior’, respectively. The results obtained in this study may contribute genetic analysis and further breeding for resistance to the common scab. [ABSTRACT FROM PUBLISHER]

MYB and bHLH are large transcription factor families with largely uncharacterized biological functions. The patterns of expression of 42 MYB and 58 bHLH transcription factor genes were examined in potato clones that were demonstrated to have variation in anthocyanin intensity and common scab resistance to assess their possible involvement in regulating these traits. The control of expression of biosynthetic enzymes in regulation of anthocyanin intensity was also evaluated. The dihydroflavonol 4-reductase ( DFR) gene, a key enzyme in the pathway, had the highest correlation with gene expression and anthocyanin intensity (quantified as levels of anthocyanidins). Expression of five uncharacterized MYB and three bHLH genes was also highly correlated with anthocyanin intensity, suggesting that they could be regulators of biosynthetic enzyme gene expression. The same potato clones were also demonstrated to have variation in resistance to Streptomyces scabiei, the causal pathogen of common scab in potato. Correlation analysis was used to show that anthocyanin intensity was not associated with common scab resistance. However, common scab resistance was correlated with expression of another two MYB and three bHLH genes, indicating that they might be involved in the regulation of the defense response of potato against the common scab pathogen. [ABSTRACT FROM AUTHOR]

Soilborne potato diseases are persistent problems in potato production and alternative management practices are needed. In this research, biocontrol agents ( Bacillus subtilis GB03 and Rhizoctonia solani hypovirulent isolate Rhs1A1) and compost amendments (from different source material), were evaluated alone and in combination, for their potential to reduce soilborne diseases and increase tuber yield over three field seasons in Maine. Both biocontrol organisms reduced multiple soilborne diseases, stem and stolon canker by 20-38 %, black scurf by 30-58 %, and common scab by 10-34 % relative to the nontreated control treatment, and the combination treatment of both biocontrol organisms together provided nominally better control than individual treatments. However, biocontrol treatments had no direct effect on tuber yield. Compost amendments from different sources all increased total and marketable tuber yield substantially (11-37 % and 17-51 %, respectively) relative to nontreated controls. However, except for some reduction of Rhizoctonia canker, compost amendments did not reduce soilborne diseases (black scurf and commons scab) in any year, and resulted in increased levels of common scab in some years (20-45 % increase). The combination compost-biocontrol treatment, although did not perform significantly better than individual component treatments, still provided indications of combined beneficial effects from both component treatments. This research demonstrated the usefulness of these approaches and combinations as additional options for reduction of soilborne diseases and increased tuber yield and can be implemented for enhanced sustainability and productivity in potato production systems. [ABSTRACT FROM AUTHOR]

Field-grown potatoes showing scab infections were sampled in two successive years and analysed for prevailing Streptomyces strains. In 2008 and 2009, 293 Streptomyces isolates were collected in Germany and analysed for morphology, pathogenicity and strain type. Isolates varied in mycelium colour, sporulation and pigmentation. Based on their morphology, no clear differentiation of species was possible. At the genetic level, sampled isolates, as well as a number of type strains from culture collections, were characterized by PCR using 16S rRNA-specific primers and PCR-RFLP of the 16S-23S internal transcribed spacer (ITS) region with Hpy99I. Using this fingerprinting approach, Streptomyces species could be differentiated genotypically. The data from this study show that diversity among scab-causing species in Germany is much higher than previously thought. Isolates belonged to various Streptomyces spp. previously associated with common scab. This is apparently the first report of pathogenic strains of S. europaeiscabiei, S. stelliscabiei, S. acidiscabiei, S. turgidiscabiei and S. bottropensis within Germany. Streptomyces europaeiscabiei was the predominant species found. Other scab-causing species were identified, but their local distribution was uneven. For most of the isolates, the presence of the txtAB gene was demonstrated, indicating pathogenicity. This analysis is one of the first reports to examine the distribution of common scab-causing species in Germany. [ABSTRACT FROM AUTHOR]

Background: Thaxtomin A (TA) is a phytotoxin produced by plant pathogenic Streptomyces spp. responsible for potato common scab. TA inhibits cellulose biosynthesis in expanding plant tissues and is essential for disease induction. Auxin treatment of various plant tissues has been repeatedly demonstrated to inhibit TA toxicity and to reduce common scab. This work utilises Arabidopsis thaliana mutants with resistance to cellulose biosynthesis inhibitors (CBIs) to investigate the interaction between TA, other CBIs and auxins. Results: Three CBI resistant A. thaliana mutants; txr1-1 (tolerance to TA), ixr1-1 (tolerance to isoxaben - IXB) and KOR1 (cellulose deficiency), showed no altered root growth response to treatment with natural or synthetic auxins, nor with the auxin efflux transport inhibitor 2,3,5-Triiodobenzoic acid (TIBA). However, all mutants had significantly enhanced tolerance to 1-napthylphthalamic acid (NPA), another auxin efflux transport inhibitor, which blocks polar auxin transport at a site distinct from TIBA. NPA tolerance of txr1-1 and ixr1-1 was further supported by electrophysiological analysis of net H+ fluxes in the mature, but not elongation zone of roots. All three mutants showed increased tolerance to IXB, but only txr1-1 showed tolerance to TA. No mutant showed enhanced tolerance to a third CBI, dichlobenil (DCB). Conclusions: We have demonstrated that plant tolerance to TA and IXB, as well as cell wall synthesis modifications in roots, have resulted in specific co-resistance to NPA but not TIBA. This suggests that CBI resistance has an impact on polar auxin efflux transport processes associated with the NPA binding protein. We also show that NPA inhibitory response in roots occurs in the mature root zone but not the elongation zone. Responses of mutants to CBIs indicate a similar, but not identical mode of action of TA and IXB, in contrast to DCB. [ABSTRACT FROM AUTHOR]

Streptomyces scabiei causes common scab, an economically important disease of potato tubers. Some authors have previously suggested that S. scabiei penetration into host plant tissue is facilitated by secretion of esterase enzymes degrading suberin, a lipidic biopolymer of the potato periderm. In the present study, S. scabiei EF-35 showed high esterase activity in suberin-containing media. This strain also exhibited esterase activity in the presence of other biopolymers, such as lignin, cutin, or xylan, but at a much lower level. In an attempt to identify the esterases involved in suberin degradation, translated open reading frames of S. scabiei 87-22 were examined for the presence of protein sequences corresponding to extracellular esterases of S. scabiei FL1 and of the fungus Coprinopsis cinerea VTT D-041011, which have previously been shown to be produced in the presence of suberin. Two putative extracellular suberinase genes, estA and sub1, were identified. The presence of these genes in several actinobacteria was investigated by Southern blot hybridization, and both genes were found in most common-scab-inducing strains. Moreover, reverse transcription - polymerase chain reaction performed with S. scabiei EF-35 showed that estA was expressed in the presence of various biopolymers, including suberin, whereas the sub1 gene appeared to be specifically expressed in the presence of suberin and cutin. [ABSTRACT FROM AUTHOR]

A new source of russet germplasm has been identified as a parent for processing and fresh market breeding programs. It was derived via bilateral sexual polyploidization following a cross between a diploid cultivated potato and the diploid wild species Solanum infundibuliforme. This clone, designated M7, is tetraploid and highly fertile, based on crossability to tetraploid germplasm. It produces large tubers with long shape and russet skin. M7 offspring produce tubers with a desirable appearance and some are resistant to cold-induced sweetening. In addition, M7 is resistant to common scab and soft rot. [ABSTRACT FROM AUTHOR]

A survey of the prevalence of skin blemish diseases in potatoes after the growing seasons of 2008 and 2009 was carried out on 247 potato lots representing different cultivars and production regions in Norway. The results showed the presence of silver scurf ( Helminthosporium solani) in all lots. Skin spot ( Polyscytalum pustulans) and black scurf ( Rhizoctonia solani) were found in 80% of the lots, and black dot ( Colletotrichum coccodes) and common scab caused by Streptomyces spp. were present in 50-70%. Also, powdery scab ( Spongospora subterranea) occurred in 65-80% of the lots, and root-lesion nematodes ( Pratylenchus spp.) were detected in 60% of the sub-samples that exhibited symptoms of common scab. [ABSTRACT FROM AUTHOR]

This study was established to determine whether the timing of liquid dairy manure application prior to planting potatoes influenced potato crop performance and the occurrence and severity of common scab ( Streptomyces spp.) and verticillium wilt ( Verticillium dahliae). Four potato ( Solanum tuberosum L.) varieties with varying levels of resistance to common scab and verticillium wilt were planted on a site treated with manure applied at 280,500 L ha to separate plot areas 18, 6, or 1 month before potato planting in each of 2 years. Total tuber yield for 2001 showed a significant interaction between time of manure application and variety, with more scab-susceptible varieties (Russet Norkotah and W-1151R) showing lower yields compared to the fertilizer control when the manure application was made 1 month before planting. In 2002, the proportion of U.S. No. 1 tubers was significantly lower when manure was applied 1 month before planting, especially for W-1151R. Tuber dry matter was significantly reduced by manure application in both years, but was not consistently related to time of manure application. Total yield was significantly decreased as common scab levels increased, and this relationship was primarily driven by the low yield/high scab levels associated with W-1151R and Russet Norkotah planted 6 or 1 month after manure application in 2001. Late-season verticillium evaluations showed highest levels in 2001 when manure was applied 1 month before planting to susceptible varieties Superior and Russet Norkotah. This experiment showed that when manure was applied immediately ahead of potato planting yields, and quality of some varieties decreased in 1 of 2 years. Therefore, it may be safer to apply manure at least 18 months prior to planting potatoes. [ABSTRACT FROM AUTHOR]

Common scab is one of the most important soil-borne diseases of potato and is difficult to control. Selection of potato breeding lines for resistance to common scab is also cumbersome due to environmental factors influencing symptom development and an erratic spatial distribution of the scab pathogens ( Streptomyces spp.) in the field. The bacterial phytotoxin thaxtomin A, which causes scab symptoms, can be used to screen large numbers of potato seedlings for tolerance in vitro, but few studies have investigated whether the results correspond to resistance to common scab observed in the field. In this study, 120 F1 potato progeny from a single cross were screened in vitro by exposing the seedlings to thaxtomin A added to the culture medium. Eighteen genotypes were selected based on high sensitivity or tolerance using shoot growth as the criterion, multiplied in vitro, and tested for resistance to common scab caused by S. turgidiscabies and S. scabies in a glasshouse and in three different fields. Evaluation of ca. 6500 tubers showed that the 18 potato genotypes differed in scab indices and disease severity ( P < 0·0001). The relative shoot height in vitro (thaxtomin A used at 0·5 μg mL) and the scab index in the field showed significant correlation ( r = −0·463, P = 0·0528, n = 18), also consistent with the results obtained under controlled conditions in the glasshouse. Hence, the in vitro bioassay may be used to discard scab-susceptible genotypes and elevate the overall levels of common scab resistance in the potato breeding populations. [ABSTRACT FROM AUTHOR]

The biocontrol agent Streptomyces melanosporofaciens strain EF-76 produces geldanamycin, an ansamycin antibiotic which displays antagonistic activity towards several Gram-positive bacteria and fungi. Biopolymers [chitin, carboxymethylcellulose (CMC) and xylan] or N-acetylglucosamine were added to S. melanosporofaciens culture media and the effect of these additional carbon sources on geldanamycin production was analysed. Geldanamycin biosynthesis was only stimulated in the presence of 1 g L-1 of chitin. Higher concentrations of chitin, as well as the presence of CMC or xylan, did not improve antibiotic production. N-acetylglucosamine, the final degradation product of chitin, did not stimulate geldanamycin production at all concentrations tested. Nevertheless, the addition of chitin in culture media had no or a negative impact on the antagonistic activity of EF-76 towards the pathogen Streptomyces scabies. Furthermore, the effect of chitin, CMC and xylan on the biocontrol ability of EF-76 against S. scabies was tested on radish seedlings. None of the polymers affected the biocontrol efficiency of EF-76 under gnotobiotic conditions. However, the addition of CMC or xylan to plant growth medium protected radish seedlings against S. scabies infection. [ABSTRACT FROM AUTHOR]

'Taedong Valley' is a high yielding and processing potato cultivar, which is a clonal selection resulting from a cross between 'W870' and 'A88431-1'. It is a medium maturating cultivar with medium plant height and light green foliage. 'Taedong Valley' has profuse flowering habit and light purple flowers. Tubers are smooth, round, and with yellow skin, light yellow flesh, medium eye depth. Tubers have medium dormancy and good keeping quality. 'Taedong Valley' has stable yield under wide range of climatic conditions. It is resistant to common scab and potato virus Y, but moderately susceptible to late blight. It is also resistant to most of the disorders, particularly dehiscence, hollow heart and internal brown spots. This cultivar has high level of tuber uniformity and capable of yielding 43.6 t/ha which is about 9.0% higher than the control potato cultivar 'Atlantic' under optimum agronomical practices. [ABSTRACT FROM AUTHOR]

Common scab, caused by Streptomyces scabies, is a disease that produces scab-like surface lesions on potato tubers. Testing for susceptibility/resistance of breeding lines at the Potato Research Centre of Agriculture & Agri-Food Canada (AFC) is carried out in a scab nursery maintained at AFC for the annual scab evaluation field trials. A replicated field trial routinely consists of breeding lines from previous testing season(s) plus newly selected lines. Data of scab scores generated from long-term experiments thus formulate an incomplete 2-way table over combinations of breeding lines (genotypes) and trials (years). This requires an advanced statistical method to estimate genetic parameters for evaluation purposes. A data base with 1,435 scab index scores from 344 breeding lines were extracted from 5 years (1995–1999) of field experiments in the scab nursery maintained at AFC. The statistical method Residual Maximum Likelihood (REML) was employed to estimate variance components of the breeding population and Best Linear Unbiased Predictor (BLUP) was used to predict genetic merit of breeding lines. High heritability was obtained from variance components estimated by REML. The BLUP scores of breeding lines provided reliable evaluation of their responses to common scab. Two data base sub-sets were separately formulated from the original data base for those parents and grandparents of the breeding lines having pedigree records available. They were again subjected to REML and BLUP analyses to compare the responses to common scab and identify sources of resistance at the parental and grandparental levels. Two random data sets with equal sized samples of breeding lines were also generated from the over-all data base. The two sets of BLUP scores between corresponding breeding lines and parents showed high association which provides an assessment of the validity of the evaluation process. [ABSTRACT FROM AUTHOR]

Abstract: Thaxtomin phytotoxins, first reported in 1989, are cyclic dipeptides (2,5-diketopiperazines) formed from the condensation of 4-nitrotrytophan and phenylalanine groups. Inclusion of a 4-nitroindole moiety that is an essential requirement for their phytotoxicity makes them unique amongst microbial generated metabolites. Individual thaxtomins differ only in the presence or absence of N-methyl and hydroxyl groups and their respective substitution sites. The name “thaxtomin” was assigned to these compounds in honor of the eminent American phytopathologist Roland Thaxter who first described the nature of the microorganisms responsible for their production. The great interest in the thaxtomins derives mainly from their established roles as virulence factors in the common scab of potato disease and their apparent ability to inhibit cellulose synthesis in developing plant cells. Surveys of comparable scab-inducing organisms from potato producing regions throughout the world have confirmed the generality of the phytotoxin associated process. Descriptions of the isolation, chemical structure determination, total synthesis, biosynthesis, transformation by microorganisms and biological activity of the thaxtomins are comprehensively reviewed. [Copyright &y& Elsevier]