Common scab

Abstract: * About the Editors * Contributors * Foreword * Preface * Chapter 1. Structure, Biosystematics, and Genetic Resources (David M. Spooner and Alberto Salas) * Structure * Origin, Spread, and Habitat * Genus Solanum * Relationships within Solanum Section Petota * Taxonomy of Section Petota * Taxonomy of Cultivated Potato * Collection, Conservation, and Use of Germplasm * Chapter 2. Genetics of Agrihorticultural Traits (John E. Bradshaw) * Genetical Methods * Flowering * Tuber Yield and Its Components * Maturity * Dormancy * Tuber Shape and Eye Depth * Pigmentation * Chapter 3. Considerations for Successful Breeding (Jai Gopal) * Reproductive Biology * Selection of Superior Parents and Crosses * Selection of Superior Clones from the Progeny * Other Options * Chapter 4. Biotechnology in Potato Improvement (Gerhard Wenzel) * Biotechnology for Conservation and Characterization of Germplasm * Breeding New Cultivars Using Biotechnology * Chapter 5. Quality Improvement (T. R. Tarn, G. C. C. Tai, and Qiang Liu) * Breeding Objectives for Quality Improvement * Genetic Improvement of Quality Traits * Chapter 6. Ecophysiology and Agronomic Management (P. M. Govindakrishnan and A. J. Haverkort) * Growth Phases * Modeling * Agroecological Zoning * Potato Growing Environments and the Role of Agrotechniques * Multiple Cropping * Chapter 7. Abiotic Stresses (Kazuto Iwama and Junichi Yamaguchi) * Physiobiochemical Basis of Tuber Formation and Bulking * Drought Stress * Heat Stress * Other Abiotic Stresses * Chapter 8. Late Blight (G. A. Forbes and J. A. Landeo) * Causal Agent * Disease Symptoms * Epidemiology and Disease Cycle * Disease Management * Chapter 9. Fungal and Oomycete Diseases (H. W. (Bud) Platt and R. D. Peters) * Foliar Diseases * Soilborne Diseases * Chapter 10. Bacterial Diseases (R. Lebecka, E. Zimnoch-Guzowska, and E. Lojkowska) * Bacterial Wilt (Brown Rot) * Ring Rot * Soft Rot and Blackleg * Common Scab * Pink Eye * Leaf Spot * Chapter 11. Viruses and Viroids (Colin Jeffries, H. Barker, and S. M. Paul Khurana) * Viruses (and Viroids) and Their Transmission * Symptoms and Detection * Management * Chapter 12. Insects, Nematodes, and IPM (Hanafi Abdelhaq) * Major Insect Pests * Major Nematode Pests * Integrated Pest Management * Chapter 13. Storage (Klaus Gottschalk and R. Ezekiel) * Physiological Age and Dormancy * Condition of Potatoes Before Storage * Storage Conditions * Storage Process * Sprout Inhibition * Biochemical Changes During Storage * Chapter 14. Processing and Value Addition (Xiu-Qing Li, Martin G. Scanlon, Qiang Liu, and Warren K. Coleman) * Food Value of Potatoes * Factors Important to the Production of Potatoes for Processing * Processing Potato into French Fries and Chips * Potato Starch * Potato Peels, Culls, and Wastewater * Molecular Farming of Value-Added Proteins in Potato * Chapter 15. True Potato Seed (Jai Gopal and R. Ortiz) * Use of TPS * Production of TPS * TPS Quality * TPS Dormancy * Breeding TPS Populations * Index * Reference Notes Included

Abstract: 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. 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. 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.

Abstract: Potato common scab, caused by Streptomyces spp., is an annual production problem for potato growers, and not effectively controlled by current methods. A field with naturally occurring common scab suppression has been identified in Michigan, and confirmed to have a biological basis for this disease suppression. This field and an adjacent scab nursery conducive to disease were studied using pyrosequencing to compare the two microbial communities. Total DNA was extracted from both the disease-conducive and -suppressive soils. A phylogenetically taxon-informative region of the 16S rRNA gene was used to establish operational taxonomic units (OTUs) to characterize bacterial community richness and diversity. In total, 1,124 OTUs were detected and 565 OTUs (10% dissimilarity) were identified in disease-conducive soil and 859 in disease-suppressive soil, including 300 shared both between sites. Common phyla based on relative sequence abundance were Acidobacteria, Proteobacteria, and Firmicutes. Sequences of Lysobacter were found in significantly higher numbers in the disease-suppressive soil, as were sequences of group 4 and group 6 Acidobacteria. The relative abundance of sequences identified as the genus Bacillus was significantly higher by an order of magnitude in the disease-conducive soil.

Abstract: Seven different 2-year rotations, consisting of barley/clover, canola, green bean, millet/rapeseed, soybean, sweet corn, and potato, all followed by potato, were assessed over 10 years (1997-2006) in a long-term cropping system trial for their effects on the development of soilborne potato diseases, tuber yield, and soil microbial communities. These same rotations were also assessed with and without the addition of a fall cover crop of no-tilled winter rye (except for barley/clover, for which underseeded ryegrass was substituted for clover) over a 4-year period. Canola and rapeseed rotations consistently reduced the severity of Rhizoctonia canker, black scurf, and common scab (18 to 38% reduction), and canola rotations resulted in higher tuber yields than continuous potato or barley/clover (6.8 to 8.2% higher). Addition of the winter rye cover crop further reduced black scurf and common scab (average 12.5 and 7.2% reduction, respectively) across all rotations. The combined effect of a canola or rapeseed rotation and winter rye cover crop reduced disease severity by 35 to 41% for black scurf and 20 to 33% for common scab relative to continuous potato with no cover crop. Verticillium wilt became a prominent disease problem only after four full rotation cycles, with high disease levels in all plots; however, incidence was lowest in barley rotations. Barley/clover and rapeseed rotations resulted in the highest soil bacterial populations and microbial activity, and all rotations had distinct effects on soil microbial community characteristics. Addition of a cover crop also resulted in increases in bacterial populations and microbial activity and had significant effects on soil microbial characteristics, in addition to slightly improving tuber yield (4% increase). Thus, in addition to positive effects in reducing erosion and improving soil quality, effective crop rotations in conjunction with planting cover crops can provide improved control of soilborne diseases. However, this study also demonstrated limitations with 2-year rotations in general, because all rotations resulted in increasing levels of common scab and Verticillium wilt over time.