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

Potato crop, currently, is the staple food crop of about 1.3 billion global population. Potato is attaining even more admiration globally day by day owing to its public acceptability. However, potato sustainable production is distinctly challenged by multiple factors like diseases, pests and climate change etc. Among diseases, common scab is one of the prime threats to potato crop due to its soil-borne nature and versatility in phytotoxins’ secretion. Common scab is caused multiple number of phytopathogenic streptomyces strains. Despite extensive research programs, researchers are still unable to identify a significant solution to this threat that is proliferating exceptional rate across the globe. To develop feasible remedies, adequate information regarding host–pathogen interaction should be available. This review possesses insights on existing pathogenic species, the evolution of novel pathogenic streptomyces spp. and phytotoxins produced by the pathogenic strains. Furthermore, which type of physiological, biochemical and genetic activities occur during pathogen’s infestation of the host are also canvassed.

Premise Apple orchards in the United States are under constant threat from a large number of pathogens and insects. Appropriate and timely deployment of disease management depends on early disease detection. Incorrect and delayed diagnosis can result in either excessive or inadequate use of chemicals, with increased production costs and increased environmental and health impacts. Methods and Results We have manually captured 3651 high‐quality, real‐life symptom images of multiple apple foliar diseases, with variable illumination, angles, surfaces, and noise. A subset of images, expert‐annotated to create a pilot data set for apple scab, cedar apple rust, and healthy leaves, was made available to the Kaggle community for the Plant Pathology Challenge as part of the Fine‐Grained Visual Categorization (FGVC) workshop at the 2020 Computer Vision and Pattern Recognition conference (CVPR 2020). Participants were asked to use the image data set to train a machine learning model to classify disease categories and develop an algorithm for disease severity quantification. The top three area under the ROC curve (AUC) values submitted to the private leaderboard were 0.98445, 0.98182, and 0.98089. We also trained an off‐the‐shelf convolutional neural network on this data for disease classification and achieved 97% accuracy on a held‐out test set. Discussion This data set will contribute toward development and deployment of machine learning–based automated plant disease classification algorithms to ultimately realize fast and accurate disease detection. We will continue to add images to the pilot data set for a larger, more comprehensive expert‐annotated data set for future Kaggle competitions and to explore more advanced methods for disease classification and quantification.

The soil‐dwelling bacterium Streptomyces scabiei is distributed worldwide and is the best‐characterised causative agent of common scab disease, which impacts potato crops and causes significant economic losses to growers. The principal pathogenicity factor responsible for common scab development is the phytotoxin thaxtomin A, which functions as a cellulose biosynthesis inhibitor in plants. S. scabiei also produces polyketide compounds belonging to the concanamycin family, which serve as inhibitors of eukaryotic vacuolar‐type ATPases and have been shown to exhibit phytotoxic activity against different plant species. It has been proposed that concanamycins contribute to the virulence of S. scabiei, but direct evidence of this has been lacking. Using constructed strains of S. scabiei that are either unable to produce concanamycins or produce elevated levels of the metabolites, we showed that concanamycins enhance the severity of disease symptoms induced by S. scabiei on radish seedlings and potato tuber tissue. We demonstrated that concanamycin production is controlled by two regulatory genes that are situated within the concanamycin biosynthetic gene cluster, and that production of concanamycins and thaxtomin A by S. scabiei is modulated by different nutritional signals. The concanamycin biosynthetic gene cluster is conserved in other common scab‐causing Streptomyces spp., suggesting that these metabolites may function as important virulence determinants in multiple phytopathogenic species. Overall, this study expands our understanding of the molecular factors that enable plant host colonisation and common scab disease development by S. scabiei. Production of concanamycins by the potato common scab pathogen Streptomyces scabiei is associated with an enhanced virulence phenotype and is controlled by genetic and environmental factors. Created using BioRender.

Powdery scab, caused by Spongospora subterranea f.sp. subterranea (Sss), is persistent soilborne disease of potato. Sss is also a vector for Potato mop-top virus (PMTV), posing another significant threat to tuber quality and marketability. Although currently available cultivars exhibit partial resistance to both Sss and PMTV, the genetic mechanisms of resistance remain poorly understood. In this study, we investigated the molecular basis of resistance to Sss and PMTV using a transcriptomics approach. Early infection time-course RNA-seq data were analyzed from three potato cultivars exhibiting differential susceptibility. Integrative analysis of differential gene expression (DGE) and gene co-expression networks (GCN) identified 80 high-confidence candidate genes associated with defense responses, comprising 52 genes associated with Sss infection and 28 with PMTV infection. These included putative immune receptor genes such as nucleotide-binding leucine-rich repeat (NLR) proteins and leucine-rich repeat receptor-like kinases (LRR-RLKs), which function as resistance (R) genes and pattern recognition receptors (PRRs), respectively. Additional candidates included phytohormone-related genes and those encoding lipoxygenase (LOX), glutathione-S-transferase (GST), and Bet v I family protein (PR10). These findings advance our understanding of host defense mechanisms against Sss and PMTV and provide molecular targets for resistance breeding and genetic improvement of commercially important potato cultivars.

Background Soil microorganisms can mediate the occurrence of plant diseases. Potato common scab (CS) is a refractory disease caused by pathogenic Streptomyces that occurs worldwide, but little is known about the interactions between CS and the soil microbiome. In this study, four soil-root system compartments (geocaulosphere soil (GS), rhizosphere soil (RS), root-zone soil (ZS), and furrow soil (FS)) were analyzed for potato plants with naturally high (H) and low (L) scab severity levels. We aimed to determine the composition and putative function of the soil microbiome associated with potato CS. Results The copy numbers of the scab phytotoxin biosynthetic gene txtAB and the bacterial 16S rRNA gene as well as the diversity and composition of each of the four soil-root system compartments were examined; GS was the only compartment that exhibited significant differences between the H and L groups. Compared to the H group, the L group exhibited a lower txtAB gene copy number, lower bacterial 16S copy number, higher diversity, higher co-occurrence network complexity, and higher community function similarity within the GS microbiome. The community composition and function of the GS samples were further revealed by shotgun metagenomic sequencing. Variovorax , Stenotrophomonas , and Agrobacterium were the most abundant genera that were significantly and positively correlated with the scab severity level, estimated absolute abundance (EAA) of pathogenic Streptomyces , and txtAB gene copy number. In contrast, Geobacillus , Curtobacterium , and unclassified Geodermatophilaceae were significantly negatively correlated with these three parameters. Compared to the function profiles in the L group, several genes involved in “ABC transporters,” the “bacterial secretion system,” “quorum sensing (QS),” “nitrogen metabolism,” and some metabolism by cytochrome P450 were enriched in the H group. In contrast, some antibiotic biosynthesis pathways were enriched in the L group. Based on the differences in community composition and function, a simple model was proposed to explain the putative relationships between the soil microbiome and CS occurrence. Conclusions The GS microbiome was closely associated with CS severity in the soil-root system, and the occurrence of CS was accompanied by changes in community composition and function. The differential functions provide new clues to elucidate the mechanism underlying the interaction between CS occurrence and the soil microbiome, and varying community compositions provide novel insights into CS occurrence.

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.

The research was conducted in 2014–2017 in a multi-cultivar apple orchard in the Experimental Orchard of the National Institute of Horticultural Research (IO-PIB) in Dąbrowice near Skierniewice. To determine the actual Venturia inaequalis ascospores release dates, the Burkard spore trap installed in a plot of the McIntosh cv. that was not protected against apple scab was used. Monitoring of ascospore releases was carried out annually, starting from the appearance of numerous colouring (maturing) ascospores in the pseudothecia (usually in the second decade of March) and ending at the second half of June, usually about two weeks after the last release of these spores. The sums of ascospores detected on a given day and their proportion in all ascospores recorded during primary infections were calculated. The obtained results formed the basis for the analysis of forecast indications of the A-scab, Metos (Metos® Pessl Instruments), and RIMpro-Venturia models in connection with meteorological data from the Metos weather station installed in this orchard and to compare them with the actual release dates recorded by the Burkard spore trap. Depending on the year, significant differences were found in the number and intensity of V. inaequalis ascospore releases and in their beginning and end dates.

The fungal genus Sacc. (anamorph Bonord.) includes plant pathogens that cause substantial economic damage to fruit crops worldwide. Although is considered a model species in plant pathology, other spp. also cause scab on other fruit trees. Relative to the substantial research that has been conducted on and apple scab, little research has been conducted on spp. affecting other fruit trees. In this review, the main characteristics of plant-pathogenic species of are discussed with special attention to affecting apple, affecting European pear, affecting Asian pear, affecting peach and almond, affecting olive, affecting pecan, and affecting loquat. This review has two main objectives: (i) to identify the main gaps in our knowledge regarding the biology and epidemiology of spp. affecting fruit trees; and (ii) to identify similarities and differences among these spp. in order to improve disease management. A thorough review has been conducted of studies regarding the phylogenetic relationships, host ranges, biologies, and epidemiologies of spp. A multiple correspondence analysis (CA) has also been performed on the main epidemiological components of these spp. CA separated the spp. into two main groups, according to their epidemiological behavior: the first group included , and , the second and , with having an intermediate position. This review shows that spp. affecting fruit trees are highly host-specific, and that important gaps in understanding the life cycle exist for some species, including ; gaps include pseudothecia formation, ascospore and conidia germination, and mycelial growth. Considering the epidemiological information reviewed, this paper shows that the use of Mills tables to predict infection periods should be avoided for spp. other than .

Potato common scab, which is caused by soil-borne Streptomyces species, is a severe plant disease that results in a significant reduction in the economic value of potatoes worldwide. Due to the lack of efficacious pesticides, crop rotations, and resistant potato cultivars against the disease, we investigated whether biological control can serve as an alternative approach. In this study, multiple Bacillus species were isolated from healthy potato tubers, and Bacillus amyloliquefaciens Ba01 was chosen for further analyses based on its potency against the potato common scab pathogen Streptomyces scabies. Ba01 inhibited the growth and sporulation of S. scabies and secreted secondary metabolites such as surfactin, iturin A, and fengycin with potential activity against S. scabies as determined by imaging mass spectrometry. In pot assays, the disease severity of potato common scab decreased from 55.6 ± 11.1% (inoculated with S. scabies only) to 4.2 ± 1.4% (inoculated with S. scabies and Ba01). In the field trial, the disease severity of potato common scab was reduced from 14.4 ± 2.9% (naturally occurring) to 5.6 ± 1.1% after Ba01 treatment, representing evidence that Bacillus species control potato common scab in nature.