Relative importance of seed-tuber and soilborne inoculum in causing black dot disease of potato

• Published in: Plant pathology Vol. 59; no. 4; pp. 693 - 702
• Main Authors: Lees, A.K, Brierley, J.L, Stewart, J.A, Hilton, A.J, Wale, S.J, Gladders, P, Bradshaw, N.J, Peters, J.C
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.08.2010; Blackwell Publishing Ltd; Blackwell; Wiley Subscription Services, Inc
• Subjects: Biological and medical sciences; Colletotrichum coccodes; Crops; Dartrose; Fundamental and applied biological sciences. Psychology; Fungal plant pathogens; Infestation; Inoculum; inoculum potential; Phytopathology. Animal pests. Plant and forest protection; Polymerase chain reaction; Progeny; real-time PCR; Soil; soil DNA extraction; Solanum tuberosum; Tubers; Plant pathology; Vegetables; Plant pathogen; Disease; Potential; real-time PCR; Fungi; Potato; Dicotyledones; Angiospermae; Tuber; Extraction; Fungi Imperfecti; Solanaceae; C3-Type; Nucleic acid; Vegetals; Soilborne transmission; Solanum tuberosum; Biochemical compound; Colletotrichum coccodes; Real time; Polymerase chain reaction; Soils; soil DNA extraction; inoculum potential; DNA; Spermatophyta; Transmission mode; Tuber plant; Molecular biology; Inoculum
• ISSN: 0032-0862; 1365-3059
• DOI: 10.1111/j.1365-3059.2010.02284.x

Controlled-environment and field experiments were done to quantify the individual contribution of seed-tuber and soilborne inoculum of Colletotrichum coccodes in causing black dot disease of potato tubers. Seed-tuber and soilborne inocula of C. coccodes were quantified using an existing real-time PCR assay and related to subsequent incidence and severity of disease. In four field trials, a controlled-environment experiment and through the monitoring of 122 commercial crops, seed-tuber inoculum was found to be relatively less important than soilborne inoculum in causing black dot, and the level of seed-tuber inoculum did not significantly affect either the incidence or severity of disease or the percentage of progeny tubers deemed unmarketable. By contrast, soilborne inoculum had the potential to result in high levels of disease and the level of C. coccodes soil infestation (pg DNA g⁻¹ soil) was found to have a significant effect. At soil infestation levels below 100 pg DNA C. coccodes g⁻¹ soil, 7% of commercial crops had an incidence of black dot greater than 20%, increasing to 40% and 57% of crops at levels of 100-1000 pg g⁻¹ and >1000 pg g⁻¹ soil, respectively. These arbitrary threshold levels for soilborne inoculum related to disease risk are discussed. Interpretation of disease risk based on inoculum levels must, in the future, be informed by agronomic variables and potential control strategies.